This document summarizes a new implementation of detailed chemical enrichment modeling in the Munich semi-analytic model of galaxy formation (L-Galaxies). The new implementation tracks the delayed enrichment of 11 heavy elements from stellar winds, supernovae type II, and supernovae type Ia. It considers different supernovae type II yield sets and three supernovae type Ia delay-time distributions. The results are compared to observational data on local star-forming galaxies, Milky Way disc G dwarfs, and local elliptical galaxies. Overall, the best model matches require a power-law supernovae type Ia delay-time distribution, supernovae type II yields accounting for prior mass loss, and some direct ejection
The pillars of_creation_revisited_with_muse_gas_kinematics_and_high_mass_stel...Sérgio Sacani
The document discusses observations of the Pillars of Creation in the Eagle Nebula using integral field spectroscopy from the MUSE instrument on the VLT. For the first time, the study maps physical parameters like extinction, density, temperature, and velocity across the pillars. The data show that the pillar tips have high densities and are being photoevaporated by the massive stars in NGC 6611. The kinematics indicate a blueshifted photoevaporative flow, consistent with simulations. The 3D geometry of the pillars is inferred, with some in front of and some behind the ionizing stars. A previously unknown outflow is detected from the middle pillar, suggesting an embedded protostar.
Third epoch magellanic_clouud_proper_motionsSérgio Sacani
The document analyzes proper motion data from the Hubble Space Telescope to study the three-dimensional rotation field of the Large Magellanic Cloud (LMC) galaxy. It finds that:
1) The proper motion data implies a stellar dynamical center that coincides with the HI dynamical center from previous studies.
2) Combining the proper motion and line-of-sight velocity data provides insights into the LMC's rotation curve, disk viewing angles, and circular rotation speed of 91.7 km/s outside the central region.
3) The data paint a consistent picture of LMC rotation and yield improved constraints on the galaxy's distance, mass profile, and orbital history around the Milky Way.
Evidence for a_complex_enrichment_history_of_the_stream_from_fairall_9_sightlineSérgio Sacani
This study analyzes absorption spectra of the Magellanic Stream (MS) toward the quasar Fairall 9, obtained using the Hubble Space Telescope Cosmic Origins Spectrograph (HST/COS) and the Very Large Telescope Ultraviolet and Visible Echelle Spectrograph (VLT/UVES). The spectra reveal absorption from multiple velocity components of the MS, indicating multiphase gas. Surprisingly, the sulfur abundance is found to be high ([S/H] = -0.30), five times higher than other MS sightlines, while the nitrogen abundance is lower ([N/H] = -1.15). This points to a complex enrichment history, where the gas toward Fair
This document summarizes the discovery of two planetary companions orbiting the metal-poor star HIP 11952 based on radial velocity measurements. The star HIP 11952 was observed over a period of 16 months using the FEROS spectrograph. Analysis of the spectra revealed periodic radial velocity variations of 6.95 days and 290 days, indicating the presence of two planets with minimum masses of 0.78 MJup and 2.93 MJup orbiting at 0.07 AU and 0.81 AU, respectively. HIP 11952 is a metal-poor star with [Fe/H] of -1.95, making it one of the few known systems with planets orbiting a star with such low metallicity
The gaia eso_survey_stellar_content_and_elemental_abundances_in_the_massive_c...Sérgio Sacani
Estudo sobre o conteúdo estelar e os elementos que estão presentes no aglomerado estelar aberto NGC 6705, também conhecido como Aglomerado do Pato Selvagem.
One tenth solar_abundances_along_the_body_of-the_streamSérgio Sacani
This document summarizes a study that analyzed spectra from four background quasars to measure the chemical abundances along the Magellanic Stream. Two key findings are:
1) The sightlines toward RBS 144 and NGC 7714 yielded metallicities of around 0.1 times the solar value, indicating a uniform low abundance along the main body of the Stream. This supports models where the Stream was stripped from the SMC around 1-2.5 billion years ago when the SMC had a metallicity of around 0.1 solar.
2) A higher metallicity of around 0.5 solar was found in the inner Stream toward Fairall 9, sampling a filament traced to the LMC. This shows the bifurc
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
The pillars of_creation_revisited_with_muse_gas_kinematics_and_high_mass_stel...Sérgio Sacani
The document discusses observations of the Pillars of Creation in the Eagle Nebula using integral field spectroscopy from the MUSE instrument on the VLT. For the first time, the study maps physical parameters like extinction, density, temperature, and velocity across the pillars. The data show that the pillar tips have high densities and are being photoevaporated by the massive stars in NGC 6611. The kinematics indicate a blueshifted photoevaporative flow, consistent with simulations. The 3D geometry of the pillars is inferred, with some in front of and some behind the ionizing stars. A previously unknown outflow is detected from the middle pillar, suggesting an embedded protostar.
Third epoch magellanic_clouud_proper_motionsSérgio Sacani
The document analyzes proper motion data from the Hubble Space Telescope to study the three-dimensional rotation field of the Large Magellanic Cloud (LMC) galaxy. It finds that:
1) The proper motion data implies a stellar dynamical center that coincides with the HI dynamical center from previous studies.
2) Combining the proper motion and line-of-sight velocity data provides insights into the LMC's rotation curve, disk viewing angles, and circular rotation speed of 91.7 km/s outside the central region.
3) The data paint a consistent picture of LMC rotation and yield improved constraints on the galaxy's distance, mass profile, and orbital history around the Milky Way.
Evidence for a_complex_enrichment_history_of_the_stream_from_fairall_9_sightlineSérgio Sacani
This study analyzes absorption spectra of the Magellanic Stream (MS) toward the quasar Fairall 9, obtained using the Hubble Space Telescope Cosmic Origins Spectrograph (HST/COS) and the Very Large Telescope Ultraviolet and Visible Echelle Spectrograph (VLT/UVES). The spectra reveal absorption from multiple velocity components of the MS, indicating multiphase gas. Surprisingly, the sulfur abundance is found to be high ([S/H] = -0.30), five times higher than other MS sightlines, while the nitrogen abundance is lower ([N/H] = -1.15). This points to a complex enrichment history, where the gas toward Fair
This document summarizes the discovery of two planetary companions orbiting the metal-poor star HIP 11952 based on radial velocity measurements. The star HIP 11952 was observed over a period of 16 months using the FEROS spectrograph. Analysis of the spectra revealed periodic radial velocity variations of 6.95 days and 290 days, indicating the presence of two planets with minimum masses of 0.78 MJup and 2.93 MJup orbiting at 0.07 AU and 0.81 AU, respectively. HIP 11952 is a metal-poor star with [Fe/H] of -1.95, making it one of the few known systems with planets orbiting a star with such low metallicity
The gaia eso_survey_stellar_content_and_elemental_abundances_in_the_massive_c...Sérgio Sacani
Estudo sobre o conteúdo estelar e os elementos que estão presentes no aglomerado estelar aberto NGC 6705, também conhecido como Aglomerado do Pato Selvagem.
One tenth solar_abundances_along_the_body_of-the_streamSérgio Sacani
This document summarizes a study that analyzed spectra from four background quasars to measure the chemical abundances along the Magellanic Stream. Two key findings are:
1) The sightlines toward RBS 144 and NGC 7714 yielded metallicities of around 0.1 times the solar value, indicating a uniform low abundance along the main body of the Stream. This supports models where the Stream was stripped from the SMC around 1-2.5 billion years ago when the SMC had a metallicity of around 0.1 solar.
2) A higher metallicity of around 0.5 solar was found in the inner Stream toward Fairall 9, sampling a filament traced to the LMC. This shows the bifurc
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
The identification of_93_day_periodic_photometric_variability_for_yso_ylw_16aSérgio Sacani
This study identifies a 93 day periodic photometric variability in the Class I young stellar object (YSO) YLW 16A in the Rho Ophiuchus star forming region. Light curve analysis reveals variations of ~0.5 magnitudes in the Ks band over this period. The authors propose a triple system model consisting of an inner binary with a 93 day period eclipsed by a warped circumbinary disk, with a tertiary companion at ~40 AU responsible for warping the disk. This model is similar to one previously proposed for another YSO, WL 4, and may indicate such triple systems with eclipsing disks are common around young stars. Understanding these systems can provide insights into stellar and planetary formation and evolution.
Proterozoic Milankovitch cycles and the history of the solar systemSérgio Sacani
The geologic record of Milankovitch climate cycles provides a rich
conceptual and temporal framework for evaluating Earth system
evolution, bestowing a sharp lens through which to view our
planet’s history. However, the utility of these cycles for constraining
the early Earth system is hindered by seemingly insurmountable
uncertainties in our knowledge of solar system behavior
(including Earth–Moon history), and poor temporal control for validation
of cycle periods (e.g., from radioisotopic dates). Here we
address these problems using a Bayesian inversion approach to
quantitatively link astronomical theory with geologic observation,
allowing a reconstruction of Proterozoic astronomical cycles, fundamental
frequencies of the solar system, the precession constant,
and the underlying geologic timescale, directly from stratigraphic
data. Application of the approach to 1.4-billion-year-old rhythmites
indicates a precession constant of 85.79 ± 2.72 arcsec/year (2σ),
an Earth–Moon distance of 340,900 ± 2,600 km (2σ), and length of
day of 18.68 ± 0.25 hours (2σ), with dominant climatic precession
cycles of ∼14 ky and eccentricity cycles of ∼131 ky. The results
confirm reduced tidal dissipation in the Proterozoic. A complementary
analysis of Eocene rhythmites (∼55 Ma) illustrates how the
approach offers a means to map out ancient solar system behavior
and Earth–Moon history using the geologic archive. The method
also provides robust quantitative uncertainties on the eccentricity
and climatic precession periods, and derived astronomical timescales.
As a consequence, the temporal resolution of ancient Earth
system processes is enhanced, and our knowledge of early solar
system dynamics is greatly improved.
TEMPORAL EVOLUTION OF THE HIGH-ENERGY IRRADIATION AND WATER CONTENT OF TRAPPI...Sérgio Sacani
The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could
harbour liquid water on their surfaces. UV observations are essential to measure their high-energy
irradiation, and to search for photodissociated water escaping from their putative atmospheres. Our
new observations of TRAPPIST-1 Ly-α line during the transit of TRAPPIST-1c show an evolution of
the star emission over three months, preventing us from assessing the presence of an extended hydrogen
exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history
of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the
orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape.
However, TRAPPIST-1e to h might have lost less than 3 Earth oceans if hydrodynamic escape stopped
once they entered the habitable zone. We caution that these estimates remain limited by the large
uncertainty on the planet masses. They likely represent upper limits on the actual water loss because
our assumptions maximize the XUV-driven escape, while photodissociation in the upper atmospheres
should be the limiting process. Late-stage outgassing could also have contributed significant amounts
of water for the outer, more massive planets after they entered the habitable zone. While our results
suggest that the outer planets are the best candidates to search for water with the JWST, they also
highlight the need for theoretical studies and complementary observations in all wavelength domains
to determine the nature of the TRAPPIST-1 planets, and their potential habitability.
Keywords: planetary systems - Stars: individual: TRAPPIST-1
Kinematics and simulations_of_the_stellar_stream_in_the_halo_of_the_umbrella_...Sérgio Sacani
This document summarizes a study of the stellar stream and substructures around the Umbrella Galaxy (NGC 4651). Deep imaging and spectroscopy were used to characterize the properties and kinematics of the stream. Tracer objects like globular clusters and planetary nebulae were identified and found to delineate a kinematically cold feature in position-velocity space. Dynamical modeling suggests the stream originated from the tidal disruption of a dwarf galaxy on a highly eccentric orbit about 6-10 billion years ago. This work demonstrates the feasibility of using discrete tracers to recover the kinematics and model the dynamics of low surface brightness stellar streams around distant galaxies.
New m embers_of_the_tw_hydrae_association_and_two_accreting_m_dwarfs_in_scorp...Sérgio Sacani
Uma descoberta acidental de uma coleção de jovens estrelas do tipo anãs vermelhas perto do nosso Sistema Solar, poderiam nos dar uma rara ideia da formação planetária em câmera lenta. Os astrônomos da The Australian National University a ANU e a University of New South Wales, a UNSW, em Canberra, descobriram grandes discos de poeira ao redor de duas estrelas, mostrando sinais de planetas em processo de formação.
“Nós achamos que a Terra e todos os planetas se formaram de discos como esses, assim é fascinante ver um potencial novo sistema solar se formando”, disse o principal pesquisador Dr. Simon Murphy, da ANU Research School of Astronomy and Astrophysics.
“Contudo, outras estrelas dessa idade normalmente não têm mais discos. Os discos das anãs vermelhas parecem viver mais do que os de estrelas mais quentes como o Sol. Nós não entendemos por que”, disse o Dr. Murphy.
DISCOVERY OF A GALAXY CLUSTER WITH A VIOLENTLY STARBURSTING CORE AT z = 2:506Sérgio Sacani
We report the discovery of a remarkable concentration of massive galaxies with extended X-ray
emission at zspec = 2:506, which contains 11 massive (M & 1011M) galaxies in the central 80kpc
region (11.6 overdensity). We have spectroscopically conrmed 17 member galaxies with 11 from CO
and the remaining ones from H. The X-ray luminosity, stellar mass content and velocity dispersion
all point to a collapsed, cluster-sized dark matter halo with mass M200c = 1013:90:2M, making it
the most distant X-ray-detected cluster known to date. Unlike other clusters discovered so far, this
structure is dominated by star-forming galaxies (SFGs) in the core with only 2 out of the 11 massive
galaxies classied as quiescent. The star formation rate (SFR) in the 80kpc core reaches 3400 M
yr 1 with a gas depletion time of 200 Myr, suggesting that we caught this cluster in rapid build-up
of a dense core. The high SFR is driven by both a high abundance of SFGs and a higher starburst
fraction ( 25%, compared to 3%-5% in the eld). The presence of both a collapsed, cluster-sized
halo and a predominant population of massive SFGs suggests that this structure could represent an
important transition phase between protoclusters and mature clusters. It provides evidence that the
main phase of massive galaxy passivization will take place after galaxies accrete onto the cluster,
providing new insights into massive cluster formation at early epochs. The large integrated stellar
mass at such high redshift challenges our understanding of massive cluster formation.
Constraints on Ceres’ internal structure and evolution from its shape and gra...Sérgio Sacani
Ceres is the largest body in the asteroid belt with a radius of
approximately 470 km. In part due to its large mass, Ceres more closely approaches
hydrostatic equilibrium than major asteroids. Pre-Dawn mission
shape observations of Ceres revealed a shape consistent with a hydrostatic
ellipsoid of revolution. The Dawn spacecraft Framing Camera has been imaging
Ceres since March 2015, which has led to high-resolution shape models
of the dwarf planet, while the gravity field has been globally determined to
a spherical harmonic degree 14 (equivalent to a spatial wavelength of 211 km)
and locally to 18 (a wavelength of 164 km). We use these shape and gravity
models to constrain Ceres’ internal structure. We find a negative correlation
and admittance between topography and gravity at degree 2 and order
2. Low admittances between spherical harmonic degrees 3 and 16 are well
explained by Airy isostatic compensation mechanism. Different models of isostasy
give crustal densities between 1200 and 1400 kg=m3 with our preferred model
This document discusses whether the [Mg/Fe] ratio is a good proxy for galaxy formation timescales. It finds that while [Mg/Fe] has traditionally been used as such a proxy, taking into account the non-universal initial mass function (IMF) observed in massive galaxies leads to unrealistic short formation timescales calculated from their [Mg/Fe] ratios. The document considers scenarios where the IMF varies with stellar population or evolves over time to potentially resolve this issue, but notes more observation of galaxies forming at high redshift is needed to better understand their chemical evolution. It concludes one must be careful interpreting [Mg/Fe] alone as a tracer of galaxy formation timescales.
The green valley_is_a_red_herring_galaxy_zoo_reveals_two_evolutionary_pathwaysSérgio Sacani
This document summarizes research using data from Galaxy Zoo, SDSS, and GALEX to study how star formation is quenched in low-redshift galaxies. The key findings are:
1) Taking galaxy morphology into account, the "green valley" is not a single transitional state, as was previously thought.
2) Only a small population of blue early-type galaxies rapidly transition across the green valley as their morphology transforms from disk to spheroid and star formation is quenched quickly.
3) The majority of blue star-forming galaxies have significant disks and retain their late-type morphology as their star formation rates decline very slowly.
4) Different evolutionary pathways are observed for early- and late-type
WHERE IS THE FLUX GOING? THE LONG-TERM PHOTOMETRIC VARIABILITY OF BOYAJIAN’S ...Sérgio Sacani
We present ∼ 800 days of photometric monitoring of Boyajian’s Star (KIC 8462852) from the AllSky
Automated Survey for Supernovae (ASAS-SN) and ∼ 4000 days of monitoring from the All Sky
Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian’s Star
has steadily decreased at a rate of 6.3 ± 1.4 mmag yr−1
, such that the star is now 1.5% fainter than it
was in February 2015. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian’s
Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a
monotonic decline. We analyze a sample of ∼ 1000 comparison stars of similar brightness located in
the same ASAS-SN field and demonstrate that the recent fading is significant at & 99.4% confidence.
The 2015 − 2017 dimming rate is consistent with that measured with Kepler data for the time period
from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models
for the star’s behavior proposed to date
The completeness-corrected rate of stellar encounters with the Sun from the f...Sérgio Sacani
I report on close encounters of stars to the Sun found in the first Gaia data release (GDR1). Combining Gaia astrometry with radial
velocities of around 320 000 stars drawn from various catalogues, I integrate orbits in a Galactic potential to identify those stars which
come within a few parsecs. Such encounters could influence the solar system, for example through gravitational perturbations of the
Oort cloud. 16 stars are found to come within 2 pc (although a few of these have dubious data). This is fewer than were found in a
similar study based on Hipparcos data, even though the present study has many more candidates. This is partly because I reject stars
with large radial velocity uncertainties (>10 km s−1
), and partly because of missing stars in GDR1 (especially at the bright end). The
closest encounter found is Gl 710, a K dwarf long-known to come close to the Sun in about 1.3 Myr. The Gaia astrometry predict
a much closer passage than pre-Gaia estimates, however: just 16 000 AU (90% confidence interval: 10 000–21 000 AU), which will
bring this star well within the Oort cloud. Using a simple model for the spatial, velocity, and luminosity distributions of stars, together
with an approximation of the observational selection function, I model the incompleteness of this Gaia-based search as a function
of the time and distance of closest approach. Applying this to a subset of the observed encounters (excluding duplicates and stars
with implausibly large velocities), I estimate the rate of stellar encounters within 5 pc averaged over the past and future 5 Myr to be
545±59 Myr−1
. Assuming a quadratic scaling of the rate within some encounter distance (which my model predicts), this corresponds
to 87 ± 9 Myr−1 within 2 pc. A more accurate analysis and assessment will be possible with future Gaia data releases.
We present spectroscopic observations of the nearby dwarf galaxy AGC 198691. This object is part
of the Survey of H I in Extremely Low-Mass Dwarfs (SHIELD) project, which is a multi-wavelength
study of galaxies with H I masses in the range of 106-107:2 M discovered by the ALFALFA survey.
We have obtained spectra of the lone H II region in AGC 198691 with the new high-throughput
KPNO Ohio State Multi-Object Spectrograph (KOSMOS) on the Mayall 4-m as well as with the Blue
Channel spectrograph on the MMT 6.5-m telescope. These observations enable the measurement of the
temperature-sensitive [O III]4363 line and hence the determination of a \direct" oxygen abundance
for AGC 198691. We nd this system to be an extremely metal-decient (XMD) system with an
oxygen abundance of 12+log(O/H) = 7.02 0.03, making AGC 198691 the lowest-abundance starforming
galaxy known in the local universe. Two of the ve lowest-abundance galaxies known have
been discovered by the ALFALFA blind H I survey; this high yield of XMD galaxies represents a
paradigm shift in the search for extremely metal-poor galaxies.
This document presents a sample of 151 dwarf galaxies that exhibit optical spectroscopic signatures of accreting massive black holes. The sample was identified by systematically searching ~25,000 emission-line galaxies from the Sloan Digital Sky Survey with stellar masses comparable to or less than the Large Magellanic Cloud. Many of the galaxies show narrow-line signatures of black hole accretion, and some also exhibit broad H-alpha emission, indicating gas orbiting in the deep potential of a massive black hole. This increases the number of known active galaxies in this low stellar mass range by over an order of magnitude. The median stellar mass of the host galaxies is around 108.5 solar masses, around 1-2 magnitudes fainter than previous samples of
Proper-motion age dating of the progeny of Nova Scorpii ad 1437Sérgio Sacani
‘Cataclysmic variables’ are binary star systems in which one
star of the pair is a white dwarf, and which often generate bright
and energetic stellar outbursts. Classical novae are one type of
outburst: when the white dwarf accretes enough matter from its
companion, the resulting hydrogen-rich atmospheric envelope
can host a runaway thermonuclear reaction that generates a rapid
brightening1–4. Achieving peak luminosities of up to one million
times that of the Sun5
, all classical novae are recurrent, on timescales
of months6
to millennia7
. During the century before and after an
eruption, the ‘novalike’ binary systems that give rise to classical
novae exhibit high rates of mass transfer to their white dwarfs8
.
Another type of outburst is the dwarf nova: these occur in binaries
that have stellar masses and periods indistinguishable from those
of novalikes9
but much lower mass-transfer rates10, when accretiondisk
instabilities11 drop matter onto the white dwarfs. The coexistence
at the same orbital period of novalike binaries and dwarf
novae—which are identical but for their widely varying accretion
rates—has been a longstanding puzzle9
. Here we report the recovery
of the binary star underlying the classical nova eruption of 11 March
ad 1437 (refs 12, 13), and independently confirm its age by propermotion
dating. We show that, almost 500 years after a classical-nova
event, the system exhibited dwarf-nova eruptions. The three other
oldest recovered classical novae14–16 display nova shells, but lack
firm post-eruption ages17,18, and are also dwarf novae at present.
We conclude that many old novae become dwarf novae for part of
the millennia between successive nova eruptions19,
Evidence for a_distant_giant_planet_in_the_solar_systemSérgio Sacani
A descoberta de um novo planeta, atualmente não é uma manchete que chama tanto assim a atenção das pessoas. Muito disso, graças ao Telescópio Espacial Kepler, que já descobriu quase 2000 exoplanetas e todo instante uma nova descoberta é anunciada, certo? Mais ou menos, a descoberta anunciada hoje, dia 20 de Janeiro de 2016, é um pouco diferente, pois não se trata de um exoplaneta, e sim de um novo planeta no Sistema Solar, e esse é um fato que intriga os astrônomos a muitos e muitos anos.
Porém, temos que ir com calma com esses anúncios. No artigo aceito para publicação no The Astronomical Journal (artigo no final do post), os autores, Mike Brown e Konstantin Batygin, do Instituto de Tecnologia da Califórnia, apresentaram o que eles dizem ser evidências circunstâncias fortes para a existência de um grande planeta ainda não descoberto, talvez, com uma massa 10 vezes a massa da Terra, orbitando os confins do nosso Sistema Solar, muito além da órbita de Plutão. Os cientistas inferiram sua presença, por meio de anomalias encontradas nas órbitas de seis objetos do chamado Cinturão de Kuiper.
O objeto, que os pesquisadores estão chamando de Planeta Nove, não chega muito perto do Sol, no ponto mais próximo da sua órbita ele fica a 30.5 bilhões de quilômetros, ou seja, cinco vezes a distância entre o Sol e Plutão. Apesar do seu grande tamanho, ele é muito apagado, e por isso ninguém até o momento conseguiu observá-lo.
Não existe ainda uma confirmação observacional da descoberta, mas as evidências são tão fortes que fizeram com que outros especialistas como Chad Trujilo do Observatório Gemini no Havaí e David Nesvorny, do Southwest Research Institute em Boulder no Colorado, ficassem impressionados e bem convencidos de que deve mesmo haver um grande planeta nas fronteiras da nossa vizinhança cósmica.
Four new planets_around_giant_stars_and_the_mass_metallicity_correlation_of_p...Sérgio Sacani
Exoplanet searches have revealed interesting correlations between the stellar properties and the occurrence rate of planets.
In particular, different independent surveys have demonstrated that giant planets are preferentially found around metal-rich stars and
that their fraction increases with the stellar mass.
Aims. During the past six years, we have conducted a radial velocity follow-up program of 166 giant stars, to detect substellar
companions, and characterizing their orbital properties. Using this information, we aim to study the role of the stellar evolution in
the orbital parameters of the companions, and to unveil possible correlations between the stellar properties and the occurrence rate of
giant planets.
Methods. We have taken multi-epoch spectra using FEROS and CHIRON for all of our targets, from which we have computed
precision radial velocities and we have derived atmospheric and physical parameters. Additionally, velocities computed from UCLES
spectra are presented here. By studying the periodic radial velocity signals, we have detected the presence of several substellar
companions.
Results. We present four new planetary systems around the giant stars HIP8541, HIP74890, HIP84056 and HIP95124. Additionally,
we study the correlation between the occurrence rate of giant planets with the stellar mass and metallicity of our targets. We find that
giant planets are more frequent around metal-rich stars, reaching a peak in the detection of f = 16.7+15.5
−5.9 % around stars with [Fe/H] ∼
0.35 dex. Similarly, we observe a positive correlation of the planet occurrence rate with the stellar mass, between M⋆∼ 1.0 - 2.1 M⊙ ,
with a maximum of f = 13.0+10.1
−4.2 %, at M⋆= 2.1 M⊙ .
Conclusions. We conclude that giant planets are preferentially formed around metal-rich stars. Also, we conclude that they are more
efficiently formed around more massive stars, in the stellar mass range of ∼ 1.0 - 2.1 M⊙ . These observational results confirm previous
findings for solar-type and post-MS hosting stars, and provide further support to the core-accretion formation model.
The yellow hypergiant HR 5171 A: Resolving a massive interacting binary in th...GOASA
HR 5171 A exhibits a complex appearance based on AMBER/VLTI observations. The observations reveal an unusually large star of approximately 1315 solar radii at a distance of 3.6 kiloparsecs. The source is surrounded by an extended nebula. The observations also show a high level of asymmetry in the brightness distribution, which is attributed to the discovery of a companion star located in front of the primary. Analysis of visual photometry data indicates the system has an orbital period of 1304 days, providing evidence it is a contact or over-contact eclipsing binary. Modeling suggests a total system mass of 39-79 solar masses and a high mass ratio of at least 10 for the companion. The discovery of the
Dissecting x ray_emitting_gas_around_the_center_of_our_galaxySérgio Sacani
1) The Chandra X-ray Observatory was used to observe the supermassive black hole at the center of the Milky Way, Sgr A*, for a total of 3 megaseconds.
2) The observations revealed extended X-ray emission around Sgr A* that aligns spatially with a surrounding disk of massive stars.
3) Spectral analysis ruled out low-mass stars as the origin of the X-ray emission and instead found evidence that the emission is from a radiatively inefficient accretion flow onto the black hole, with an outflow present.
Alignment of th_angular_momentum_vectors_of_planetary_nebulae_in_the_galactic...Sérgio Sacani
This document analyzes the orientations of 130 planetary nebulae (PNe) in the Galactic Bulge to investigate whether there is a preferred alignment. It finds that while the full sample shows a uniform distribution, the bipolar PNe exhibit a non-uniform distribution with a mean orientation along the Galactic plane at a 90 degree position angle, significant at the 0.001 level. This indicates that the orbital planes of binary systems in old stars are oriented perpendicular to the Galactic plane, likely due to strong magnetic fields during star formation that influenced the angular momentum vectors.
The identification of_93_day_periodic_photometric_variability_for_yso_ylw_16aSérgio Sacani
This study identifies a 93 day periodic photometric variability in the Class I young stellar object (YSO) YLW 16A in the Rho Ophiuchus star forming region. Light curve analysis reveals variations of ~0.5 magnitudes in the Ks band over this period. The authors propose a triple system model consisting of an inner binary with a 93 day period eclipsed by a warped circumbinary disk, with a tertiary companion at ~40 AU responsible for warping the disk. This model is similar to one previously proposed for another YSO, WL 4, and may indicate such triple systems with eclipsing disks are common around young stars. Understanding these systems can provide insights into stellar and planetary formation and evolution.
Proterozoic Milankovitch cycles and the history of the solar systemSérgio Sacani
The geologic record of Milankovitch climate cycles provides a rich
conceptual and temporal framework for evaluating Earth system
evolution, bestowing a sharp lens through which to view our
planet’s history. However, the utility of these cycles for constraining
the early Earth system is hindered by seemingly insurmountable
uncertainties in our knowledge of solar system behavior
(including Earth–Moon history), and poor temporal control for validation
of cycle periods (e.g., from radioisotopic dates). Here we
address these problems using a Bayesian inversion approach to
quantitatively link astronomical theory with geologic observation,
allowing a reconstruction of Proterozoic astronomical cycles, fundamental
frequencies of the solar system, the precession constant,
and the underlying geologic timescale, directly from stratigraphic
data. Application of the approach to 1.4-billion-year-old rhythmites
indicates a precession constant of 85.79 ± 2.72 arcsec/year (2σ),
an Earth–Moon distance of 340,900 ± 2,600 km (2σ), and length of
day of 18.68 ± 0.25 hours (2σ), with dominant climatic precession
cycles of ∼14 ky and eccentricity cycles of ∼131 ky. The results
confirm reduced tidal dissipation in the Proterozoic. A complementary
analysis of Eocene rhythmites (∼55 Ma) illustrates how the
approach offers a means to map out ancient solar system behavior
and Earth–Moon history using the geologic archive. The method
also provides robust quantitative uncertainties on the eccentricity
and climatic precession periods, and derived astronomical timescales.
As a consequence, the temporal resolution of ancient Earth
system processes is enhanced, and our knowledge of early solar
system dynamics is greatly improved.
TEMPORAL EVOLUTION OF THE HIGH-ENERGY IRRADIATION AND WATER CONTENT OF TRAPPI...Sérgio Sacani
The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could
harbour liquid water on their surfaces. UV observations are essential to measure their high-energy
irradiation, and to search for photodissociated water escaping from their putative atmospheres. Our
new observations of TRAPPIST-1 Ly-α line during the transit of TRAPPIST-1c show an evolution of
the star emission over three months, preventing us from assessing the presence of an extended hydrogen
exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history
of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the
orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape.
However, TRAPPIST-1e to h might have lost less than 3 Earth oceans if hydrodynamic escape stopped
once they entered the habitable zone. We caution that these estimates remain limited by the large
uncertainty on the planet masses. They likely represent upper limits on the actual water loss because
our assumptions maximize the XUV-driven escape, while photodissociation in the upper atmospheres
should be the limiting process. Late-stage outgassing could also have contributed significant amounts
of water for the outer, more massive planets after they entered the habitable zone. While our results
suggest that the outer planets are the best candidates to search for water with the JWST, they also
highlight the need for theoretical studies and complementary observations in all wavelength domains
to determine the nature of the TRAPPIST-1 planets, and their potential habitability.
Keywords: planetary systems - Stars: individual: TRAPPIST-1
Kinematics and simulations_of_the_stellar_stream_in_the_halo_of_the_umbrella_...Sérgio Sacani
This document summarizes a study of the stellar stream and substructures around the Umbrella Galaxy (NGC 4651). Deep imaging and spectroscopy were used to characterize the properties and kinematics of the stream. Tracer objects like globular clusters and planetary nebulae were identified and found to delineate a kinematically cold feature in position-velocity space. Dynamical modeling suggests the stream originated from the tidal disruption of a dwarf galaxy on a highly eccentric orbit about 6-10 billion years ago. This work demonstrates the feasibility of using discrete tracers to recover the kinematics and model the dynamics of low surface brightness stellar streams around distant galaxies.
New m embers_of_the_tw_hydrae_association_and_two_accreting_m_dwarfs_in_scorp...Sérgio Sacani
Uma descoberta acidental de uma coleção de jovens estrelas do tipo anãs vermelhas perto do nosso Sistema Solar, poderiam nos dar uma rara ideia da formação planetária em câmera lenta. Os astrônomos da The Australian National University a ANU e a University of New South Wales, a UNSW, em Canberra, descobriram grandes discos de poeira ao redor de duas estrelas, mostrando sinais de planetas em processo de formação.
“Nós achamos que a Terra e todos os planetas se formaram de discos como esses, assim é fascinante ver um potencial novo sistema solar se formando”, disse o principal pesquisador Dr. Simon Murphy, da ANU Research School of Astronomy and Astrophysics.
“Contudo, outras estrelas dessa idade normalmente não têm mais discos. Os discos das anãs vermelhas parecem viver mais do que os de estrelas mais quentes como o Sol. Nós não entendemos por que”, disse o Dr. Murphy.
DISCOVERY OF A GALAXY CLUSTER WITH A VIOLENTLY STARBURSTING CORE AT z = 2:506Sérgio Sacani
We report the discovery of a remarkable concentration of massive galaxies with extended X-ray
emission at zspec = 2:506, which contains 11 massive (M & 1011M) galaxies in the central 80kpc
region (11.6 overdensity). We have spectroscopically conrmed 17 member galaxies with 11 from CO
and the remaining ones from H. The X-ray luminosity, stellar mass content and velocity dispersion
all point to a collapsed, cluster-sized dark matter halo with mass M200c = 1013:90:2M, making it
the most distant X-ray-detected cluster known to date. Unlike other clusters discovered so far, this
structure is dominated by star-forming galaxies (SFGs) in the core with only 2 out of the 11 massive
galaxies classied as quiescent. The star formation rate (SFR) in the 80kpc core reaches 3400 M
yr 1 with a gas depletion time of 200 Myr, suggesting that we caught this cluster in rapid build-up
of a dense core. The high SFR is driven by both a high abundance of SFGs and a higher starburst
fraction ( 25%, compared to 3%-5% in the eld). The presence of both a collapsed, cluster-sized
halo and a predominant population of massive SFGs suggests that this structure could represent an
important transition phase between protoclusters and mature clusters. It provides evidence that the
main phase of massive galaxy passivization will take place after galaxies accrete onto the cluster,
providing new insights into massive cluster formation at early epochs. The large integrated stellar
mass at such high redshift challenges our understanding of massive cluster formation.
Constraints on Ceres’ internal structure and evolution from its shape and gra...Sérgio Sacani
Ceres is the largest body in the asteroid belt with a radius of
approximately 470 km. In part due to its large mass, Ceres more closely approaches
hydrostatic equilibrium than major asteroids. Pre-Dawn mission
shape observations of Ceres revealed a shape consistent with a hydrostatic
ellipsoid of revolution. The Dawn spacecraft Framing Camera has been imaging
Ceres since March 2015, which has led to high-resolution shape models
of the dwarf planet, while the gravity field has been globally determined to
a spherical harmonic degree 14 (equivalent to a spatial wavelength of 211 km)
and locally to 18 (a wavelength of 164 km). We use these shape and gravity
models to constrain Ceres’ internal structure. We find a negative correlation
and admittance between topography and gravity at degree 2 and order
2. Low admittances between spherical harmonic degrees 3 and 16 are well
explained by Airy isostatic compensation mechanism. Different models of isostasy
give crustal densities between 1200 and 1400 kg=m3 with our preferred model
This document discusses whether the [Mg/Fe] ratio is a good proxy for galaxy formation timescales. It finds that while [Mg/Fe] has traditionally been used as such a proxy, taking into account the non-universal initial mass function (IMF) observed in massive galaxies leads to unrealistic short formation timescales calculated from their [Mg/Fe] ratios. The document considers scenarios where the IMF varies with stellar population or evolves over time to potentially resolve this issue, but notes more observation of galaxies forming at high redshift is needed to better understand their chemical evolution. It concludes one must be careful interpreting [Mg/Fe] alone as a tracer of galaxy formation timescales.
The green valley_is_a_red_herring_galaxy_zoo_reveals_two_evolutionary_pathwaysSérgio Sacani
This document summarizes research using data from Galaxy Zoo, SDSS, and GALEX to study how star formation is quenched in low-redshift galaxies. The key findings are:
1) Taking galaxy morphology into account, the "green valley" is not a single transitional state, as was previously thought.
2) Only a small population of blue early-type galaxies rapidly transition across the green valley as their morphology transforms from disk to spheroid and star formation is quenched quickly.
3) The majority of blue star-forming galaxies have significant disks and retain their late-type morphology as their star formation rates decline very slowly.
4) Different evolutionary pathways are observed for early- and late-type
WHERE IS THE FLUX GOING? THE LONG-TERM PHOTOMETRIC VARIABILITY OF BOYAJIAN’S ...Sérgio Sacani
We present ∼ 800 days of photometric monitoring of Boyajian’s Star (KIC 8462852) from the AllSky
Automated Survey for Supernovae (ASAS-SN) and ∼ 4000 days of monitoring from the All Sky
Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian’s Star
has steadily decreased at a rate of 6.3 ± 1.4 mmag yr−1
, such that the star is now 1.5% fainter than it
was in February 2015. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian’s
Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a
monotonic decline. We analyze a sample of ∼ 1000 comparison stars of similar brightness located in
the same ASAS-SN field and demonstrate that the recent fading is significant at & 99.4% confidence.
The 2015 − 2017 dimming rate is consistent with that measured with Kepler data for the time period
from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models
for the star’s behavior proposed to date
The completeness-corrected rate of stellar encounters with the Sun from the f...Sérgio Sacani
I report on close encounters of stars to the Sun found in the first Gaia data release (GDR1). Combining Gaia astrometry with radial
velocities of around 320 000 stars drawn from various catalogues, I integrate orbits in a Galactic potential to identify those stars which
come within a few parsecs. Such encounters could influence the solar system, for example through gravitational perturbations of the
Oort cloud. 16 stars are found to come within 2 pc (although a few of these have dubious data). This is fewer than were found in a
similar study based on Hipparcos data, even though the present study has many more candidates. This is partly because I reject stars
with large radial velocity uncertainties (>10 km s−1
), and partly because of missing stars in GDR1 (especially at the bright end). The
closest encounter found is Gl 710, a K dwarf long-known to come close to the Sun in about 1.3 Myr. The Gaia astrometry predict
a much closer passage than pre-Gaia estimates, however: just 16 000 AU (90% confidence interval: 10 000–21 000 AU), which will
bring this star well within the Oort cloud. Using a simple model for the spatial, velocity, and luminosity distributions of stars, together
with an approximation of the observational selection function, I model the incompleteness of this Gaia-based search as a function
of the time and distance of closest approach. Applying this to a subset of the observed encounters (excluding duplicates and stars
with implausibly large velocities), I estimate the rate of stellar encounters within 5 pc averaged over the past and future 5 Myr to be
545±59 Myr−1
. Assuming a quadratic scaling of the rate within some encounter distance (which my model predicts), this corresponds
to 87 ± 9 Myr−1 within 2 pc. A more accurate analysis and assessment will be possible with future Gaia data releases.
We present spectroscopic observations of the nearby dwarf galaxy AGC 198691. This object is part
of the Survey of H I in Extremely Low-Mass Dwarfs (SHIELD) project, which is a multi-wavelength
study of galaxies with H I masses in the range of 106-107:2 M discovered by the ALFALFA survey.
We have obtained spectra of the lone H II region in AGC 198691 with the new high-throughput
KPNO Ohio State Multi-Object Spectrograph (KOSMOS) on the Mayall 4-m as well as with the Blue
Channel spectrograph on the MMT 6.5-m telescope. These observations enable the measurement of the
temperature-sensitive [O III]4363 line and hence the determination of a \direct" oxygen abundance
for AGC 198691. We nd this system to be an extremely metal-decient (XMD) system with an
oxygen abundance of 12+log(O/H) = 7.02 0.03, making AGC 198691 the lowest-abundance starforming
galaxy known in the local universe. Two of the ve lowest-abundance galaxies known have
been discovered by the ALFALFA blind H I survey; this high yield of XMD galaxies represents a
paradigm shift in the search for extremely metal-poor galaxies.
This document presents a sample of 151 dwarf galaxies that exhibit optical spectroscopic signatures of accreting massive black holes. The sample was identified by systematically searching ~25,000 emission-line galaxies from the Sloan Digital Sky Survey with stellar masses comparable to or less than the Large Magellanic Cloud. Many of the galaxies show narrow-line signatures of black hole accretion, and some also exhibit broad H-alpha emission, indicating gas orbiting in the deep potential of a massive black hole. This increases the number of known active galaxies in this low stellar mass range by over an order of magnitude. The median stellar mass of the host galaxies is around 108.5 solar masses, around 1-2 magnitudes fainter than previous samples of
Proper-motion age dating of the progeny of Nova Scorpii ad 1437Sérgio Sacani
‘Cataclysmic variables’ are binary star systems in which one
star of the pair is a white dwarf, and which often generate bright
and energetic stellar outbursts. Classical novae are one type of
outburst: when the white dwarf accretes enough matter from its
companion, the resulting hydrogen-rich atmospheric envelope
can host a runaway thermonuclear reaction that generates a rapid
brightening1–4. Achieving peak luminosities of up to one million
times that of the Sun5
, all classical novae are recurrent, on timescales
of months6
to millennia7
. During the century before and after an
eruption, the ‘novalike’ binary systems that give rise to classical
novae exhibit high rates of mass transfer to their white dwarfs8
.
Another type of outburst is the dwarf nova: these occur in binaries
that have stellar masses and periods indistinguishable from those
of novalikes9
but much lower mass-transfer rates10, when accretiondisk
instabilities11 drop matter onto the white dwarfs. The coexistence
at the same orbital period of novalike binaries and dwarf
novae—which are identical but for their widely varying accretion
rates—has been a longstanding puzzle9
. Here we report the recovery
of the binary star underlying the classical nova eruption of 11 March
ad 1437 (refs 12, 13), and independently confirm its age by propermotion
dating. We show that, almost 500 years after a classical-nova
event, the system exhibited dwarf-nova eruptions. The three other
oldest recovered classical novae14–16 display nova shells, but lack
firm post-eruption ages17,18, and are also dwarf novae at present.
We conclude that many old novae become dwarf novae for part of
the millennia between successive nova eruptions19,
Evidence for a_distant_giant_planet_in_the_solar_systemSérgio Sacani
A descoberta de um novo planeta, atualmente não é uma manchete que chama tanto assim a atenção das pessoas. Muito disso, graças ao Telescópio Espacial Kepler, que já descobriu quase 2000 exoplanetas e todo instante uma nova descoberta é anunciada, certo? Mais ou menos, a descoberta anunciada hoje, dia 20 de Janeiro de 2016, é um pouco diferente, pois não se trata de um exoplaneta, e sim de um novo planeta no Sistema Solar, e esse é um fato que intriga os astrônomos a muitos e muitos anos.
Porém, temos que ir com calma com esses anúncios. No artigo aceito para publicação no The Astronomical Journal (artigo no final do post), os autores, Mike Brown e Konstantin Batygin, do Instituto de Tecnologia da Califórnia, apresentaram o que eles dizem ser evidências circunstâncias fortes para a existência de um grande planeta ainda não descoberto, talvez, com uma massa 10 vezes a massa da Terra, orbitando os confins do nosso Sistema Solar, muito além da órbita de Plutão. Os cientistas inferiram sua presença, por meio de anomalias encontradas nas órbitas de seis objetos do chamado Cinturão de Kuiper.
O objeto, que os pesquisadores estão chamando de Planeta Nove, não chega muito perto do Sol, no ponto mais próximo da sua órbita ele fica a 30.5 bilhões de quilômetros, ou seja, cinco vezes a distância entre o Sol e Plutão. Apesar do seu grande tamanho, ele é muito apagado, e por isso ninguém até o momento conseguiu observá-lo.
Não existe ainda uma confirmação observacional da descoberta, mas as evidências são tão fortes que fizeram com que outros especialistas como Chad Trujilo do Observatório Gemini no Havaí e David Nesvorny, do Southwest Research Institute em Boulder no Colorado, ficassem impressionados e bem convencidos de que deve mesmo haver um grande planeta nas fronteiras da nossa vizinhança cósmica.
Four new planets_around_giant_stars_and_the_mass_metallicity_correlation_of_p...Sérgio Sacani
Exoplanet searches have revealed interesting correlations between the stellar properties and the occurrence rate of planets.
In particular, different independent surveys have demonstrated that giant planets are preferentially found around metal-rich stars and
that their fraction increases with the stellar mass.
Aims. During the past six years, we have conducted a radial velocity follow-up program of 166 giant stars, to detect substellar
companions, and characterizing their orbital properties. Using this information, we aim to study the role of the stellar evolution in
the orbital parameters of the companions, and to unveil possible correlations between the stellar properties and the occurrence rate of
giant planets.
Methods. We have taken multi-epoch spectra using FEROS and CHIRON for all of our targets, from which we have computed
precision radial velocities and we have derived atmospheric and physical parameters. Additionally, velocities computed from UCLES
spectra are presented here. By studying the periodic radial velocity signals, we have detected the presence of several substellar
companions.
Results. We present four new planetary systems around the giant stars HIP8541, HIP74890, HIP84056 and HIP95124. Additionally,
we study the correlation between the occurrence rate of giant planets with the stellar mass and metallicity of our targets. We find that
giant planets are more frequent around metal-rich stars, reaching a peak in the detection of f = 16.7+15.5
−5.9 % around stars with [Fe/H] ∼
0.35 dex. Similarly, we observe a positive correlation of the planet occurrence rate with the stellar mass, between M⋆∼ 1.0 - 2.1 M⊙ ,
with a maximum of f = 13.0+10.1
−4.2 %, at M⋆= 2.1 M⊙ .
Conclusions. We conclude that giant planets are preferentially formed around metal-rich stars. Also, we conclude that they are more
efficiently formed around more massive stars, in the stellar mass range of ∼ 1.0 - 2.1 M⊙ . These observational results confirm previous
findings for solar-type and post-MS hosting stars, and provide further support to the core-accretion formation model.
The yellow hypergiant HR 5171 A: Resolving a massive interacting binary in th...GOASA
HR 5171 A exhibits a complex appearance based on AMBER/VLTI observations. The observations reveal an unusually large star of approximately 1315 solar radii at a distance of 3.6 kiloparsecs. The source is surrounded by an extended nebula. The observations also show a high level of asymmetry in the brightness distribution, which is attributed to the discovery of a companion star located in front of the primary. Analysis of visual photometry data indicates the system has an orbital period of 1304 days, providing evidence it is a contact or over-contact eclipsing binary. Modeling suggests a total system mass of 39-79 solar masses and a high mass ratio of at least 10 for the companion. The discovery of the
Dissecting x ray_emitting_gas_around_the_center_of_our_galaxySérgio Sacani
1) The Chandra X-ray Observatory was used to observe the supermassive black hole at the center of the Milky Way, Sgr A*, for a total of 3 megaseconds.
2) The observations revealed extended X-ray emission around Sgr A* that aligns spatially with a surrounding disk of massive stars.
3) Spectral analysis ruled out low-mass stars as the origin of the X-ray emission and instead found evidence that the emission is from a radiatively inefficient accretion flow onto the black hole, with an outflow present.
Alignment of th_angular_momentum_vectors_of_planetary_nebulae_in_the_galactic...Sérgio Sacani
This document analyzes the orientations of 130 planetary nebulae (PNe) in the Galactic Bulge to investigate whether there is a preferred alignment. It finds that while the full sample shows a uniform distribution, the bipolar PNe exhibit a non-uniform distribution with a mean orientation along the Galactic plane at a 90 degree position angle, significant at the 0.001 level. This indicates that the orbital planes of binary systems in old stars are oriented perpendicular to the Galactic plane, likely due to strong magnetic fields during star formation that influenced the angular momentum vectors.
High precision abundances_of_the_old_solar_twin_insights_on_li_depletion_from...Sérgio Sacani
- The document presents the results of a chemical abundance analysis of the old solar twin star HIP 102152 (8.2 Gyr) and the younger solar twin 18 Sco (2.9 Gyr) using high-resolution UVES spectra.
- Abundances of 21 elements were derived for HIP 102152 with precisions up to 0.004 dex relative to the Sun. The metallicity of HIP 102152 was found to be nearly solar at [Fe/H] = -0.013.
- Elemental abundances as a function of condensation temperature reveal a solar abundance pattern for HIP 102152, unlike most solar twins. Its pattern most closely matches the Sun. The Li abundance
The document is a scientific paper published in 1972 that consists of the same citation repeated multiple times without any other substantive information. In 3 sentences or less, it is difficult to summarize the content and purpose of the document since it only contains a repeated citation without any other details.
1) The Tunable Laser Spectrometer on the Curiosity rover measured methane in the Martian atmosphere on six occasions and found no detection of methane, with an upper limit of 1.3 parts per billion.
2) This contradicts previous orbital and ground-based observations over the last decade that reported detectable methane plumes containing tens of parts per billion of methane.
3) The low measured methane level is not consistent with calculations of methane dispersal from previous large plume detections and suggests methane is being destroyed more rapidly than can be explained by current models.
Human and natural_influences_on_the_changing_thermal_structure_of_the_atmosphereSérgio Sacani
This document analyzes human and natural influences on changing atmospheric temperature patterns based on climate model simulations and satellite observations. The key findings are:
1) Both climate model simulations including human factors and satellite data show widespread tropospheric warming and stratospheric cooling over the past several decades.
2) These temperature changes are unlikely to be due to internal variability or natural external factors alone, based on comparisons to model runs with only natural forcings.
3) The observed temperature pattern matches that expected from increased greenhouse gases more closely than patterns from alternative forcings, providing evidence of a human influence on atmospheric temperatures.
The x-ray diffraction analysis of soil samples from Rocknest at Gale Crater on Mars revealed:
1) Crystalline components including plagioclase, olivine, augite, pigeonite, and minor amounts of other phases.
2) 27±14% of the soil was amorphous material, likely containing multiple iron-bearing and volatile phases including possibly hisingerite.
3) The crystalline components are similar to martian basalts and meteorites, while the amorphous component is similar to soils on Earth like those on Mauna Kea, Hawaii.
The ChemCam instrument on the Curiosity rover identified two main soil types on Mars - a fine-grained mafic soil and a coarse-grained felsic soil locally derived. The mafic soil is similar to widespread martian soils and dust, and possesses a ubiquitous hydrogen signature from hydrated amorphous phases. This hydration may account for a significant fraction of hydrogen detected globally on Mars. ChemCam analyses did not reveal water vapor exchange between the soil and atmosphere. The observations provide constraints on the nature and hydration of amorphous phases in the soil.
Its official voyager_has_left_the_solar_systemSérgio Sacani
1) After 36 years of traveling away from Earth, the Voyager 1 spacecraft may have finally crossed into interstellar space based on new data.
2) In August 2012, Voyager 1 detected a sharp drop in cosmic rays from inside the heliosphere and an increase in cosmic rays from outside, but the magnetic field did not change direction as expected. This led to debate over whether it had truly crossed the boundary.
3) In April 2013, Voyager detected plasma oscillations at a frequency implying a plasma density 80 times higher than inside the heliosphere, suggesting it had crossed into interstellar space in August 2012. While some researchers still disagree, this is now the consensus of the Voyager team.
A rigid and_weathered_ice_shell_on_titanSérgio Sacani
- Saturn's moon Titan likely has a global subsurface ocean beneath an ice shell 50-200 km thick.
- Analysis of gravity and topography data at long wavelengths shows a strong inverse correlation, indicating a rigid ice shell at least 40 km thick.
- A rigid shell is required to support hundreds of meters of surface erosion/deposition as observed, ruling out an actively convecting shell.
- The results suggest Titan's ice shell has undergone substantial erosion over geological timescales, with implications for its internal structure and composition.
Swiging between rotation_and_accretion_power_in_a_millisecond_binary_pulsarSérgio Sacani
This document discusses the discovery of a millisecond X-ray pulsar, IGR J18245-2452, located in the globular cluster M28. The pulsar was previously known as the radio millisecond pulsar PSR J1824-2452I. Observations found that the pulsar alternates between accretion-powered and rotation-powered states on timescales of years, providing direct evidence that these two states cycle in recycled pulsars. When accreting, the pulsar shows X-ray pulsations and luminosity characteristic of other accreting millisecond pulsars. When not accreting, it had previously been detected as a radio pulsar. This demonstrates the evolutionary link between low-mass X
Inference of homogeneous_clouds_in_an_exoplanet_atmosphereSérgio Sacani
1) New visible and infrared observations of the exoplanet Kepler-7b were analyzed to determine its atmospheric properties and detect the presence of clouds.
2) The observations found a westward shift in Kepler-7b's optical phase curve and placed upper limits on its thermal emission that remained undetected in Spitzer bandpasses.
3) The data suggests Kepler-7b has optically thick, high-altitude clouds located west of the substellar point, composed possibly of silicates. The clouds help explain Kepler-7b's unusually high geometric albedo and visible flux that cannot be attributed to thermal emission or molecular hydrogen scattering alone.
Mapping the three_dimensional_density_of_the_galactic_bulge_with_vvv_red_clum...Sérgio Sacani
This document summarizes a study that mapped the three-dimensional density distribution of the Galactic bulge using red clump giant stars identified in the VISTA Variables in the Via Lactea (VVV) survey. The authors constructed extinction maps and used the red clump stars to estimate line-of-sight density distributions by deconvolving the intrinsic luminosity function. Assuming an 8-fold mirror symmetry, they used the line-of-sight densities to construct a 3D density map covering the inner (2.2 × 1.4 × 1.1)kpc of the bulge/bar. The resulting density distribution shows a highly elongated bar with an exponential fall off and axis ratios characteristic of a strongly boxy/pe
This document summarizes research on determining temperatures, luminosities, and masses of the coldest known brown dwarfs. The key findings are:
1) Precise distances were measured for a sample of late-T and Y dwarfs using Spitzer Space Telescope astrometry, allowing accurate calculation of absolute fluxes, luminosities, and temperatures.
2) Y0 dwarfs were found to have temperatures of 400-450 K, significantly warmer than previous estimates, and masses of 5-20 times Jupiter's mass.
3) While having similar temperatures, Y dwarfs showed diverse spectral energy distributions, suggesting temperature alone does not determine spectra. Physical properties like gravity, clouds and chemistry also influence spectra.
In situ observations_of_interstellar_plasma_with_voyager_1Sérgio Sacani
Voyager 1 detected electron plasma oscillations beginning in April 2013 at a frequency corresponding to an electron density of 0.08 cm-3. This provides evidence that Voyager 1 has crossed into the nearby interstellar plasma, as the density is much higher than what is expected in the heliosheath. Comparison with radio emissions detected in 1992 suggests Voyager 1 has encountered a smoothly increasing plasma density ramp, as the frequency drift matches what was observed remotely. Estimating the shock propagation speed that would be required to produce the 1992 drift indicates a plausible speed of 40 km/s.
The petrochemistry of_jake_m_a_martian_mugeariteSérgio Sacani
The rock "Jake_M" was the first rock analyzed by Curiosity on Mars. It has a distinct chemical composition compared to other known Martian rocks. Jake_M has a basaltic composition but is alkaline, with over 15% normative nepheline content. Its chemical makeup is similar to terrestrial mugearites, fractionated alkaline rocks found at ocean islands and rifts. This suggests Jake_M formed through extensive fractional crystallization of an alkaline magma at elevated pressure, possibly with water. The discovery of an alkaline rock expands the diversity of known Martian igneous compositions.
Curiosity at gale_crater_characterization_and_analysis_of_the_rocknest_sand_s...Sérgio Sacani
The Rocknest sand shadow analyzed by the Curiosity rover on Mars was similar to coarse-grained ripples analyzed by previous rovers. It consisted of an upper layer of very coarse sand grains armoring the surface, underlain by finer grains. Analysis found the sand was around 55% crystalline material of basaltic composition and 45% amorphous iron-rich glass. This amorphous component contained the volatiles detected and was similar to soils analyzed at other Mars sites, implying the materials were locally derived from similar basaltic sources globally on Mars.
The Curiosity rover analyzed samples of Martian fines from the Rocknest site using its Sample Analysis at Mars (SAM) instrument suite. SAM detected water, sulfur dioxide, carbon dioxide, and oxygen as the major gases released when heating the fines. The water content and release temperature suggest the water is bound in amorphous materials. Much of the carbon dioxide was likely released from the decomposition of fine-grained iron or magnesium carbonates. Elevated levels of deuterium indicate recent interaction with the atmosphere. Several simple organic compounds were detected but are not definitively of Martian origin.
Evidence of rocky_planetesimals_orbiting_two_hyades_starsSérgio Sacani
This document summarizes evidence of rocky planetesimals orbiting two white dwarf stars (WD 0421+162 and WD 0431+126) that were originally intermediate-mass stars in the Hyades open star cluster. Hubble Space Telescope ultraviolet spectroscopy of the two white dwarfs detected silicon absorption lines, indicating ongoing accretion of silicon-rich material, along with upper limits on carbon that suggest the polluting material is more carbon-deficient than chondritic meteorites and thus rocky in composition. The observations are consistent with rocky planetesimals and small planets having formed around the two main-sequence progenitor stars in the Hyades, with the white dwarf descendants now showing signs of accretion from this planetary debris.
Betelgeuse as a Merger of a Massive Star with a CompanionSérgio Sacani
This document summarizes a study that uses 3D hydrodynamic simulations and 1D stellar evolution modeling to investigate the merger of a 16 solar mass star with a 4 solar mass companion star. The simulations show the companion spirals inward and merges with the primary star's helium core. Approximately 0.6 solar masses of material is ejected in an asymmetric, bipolar outflow. The post-merger structure is then modeled in 1D stellar evolution, showing in some cases the star evolves to have surface properties similar to Betelgeus, with rapid rotation and enhanced nitrogen at the surface. This pioneering study aims to comprehensively model stellar mergers across dynamical, thermal, and nuclear evolutionary timescales.
Cold Molecular Gas in Merger Remnants. I. Formation of Molecular Gas DiscsGOASA
- 80% (24/30) of the merger remnants with robust CO detections showed kinematical signatures of rotating molecular gas disks (including nuclear rings) based on their velocity fields. The sizes of these disks varied significantly from 1.1 kpc to 9.3 kpc.
- In 54% of the sources, the size of the molecular gas disks was more compact than the K-band effective radius, possibly formed from past gas inflows triggered by dynamical instabilities during mergers.
- The remaining 46% had more extended gas disks relative to the stellar component, possibly forming late-type galaxies with central stellar bulges.
- The study suggests that nuclear and extended molecular gas disks are common in
Exploring the nature and synchronicity of early cluster formation in the Larg...Sérgio Sacani
We analyse Hubble Space Telescope observations of six globular clusters in the Large Magel- lanic Cloud (LMC) from programme GO-14164 in Cycle 23. These are the deepest available observations of the LMC globular cluster population; their uniformity facilitates a precise comparison with globular clusters in the Milky Way. Measuring the magnitude of the main- sequence turn-off point relative to template Galactic globular clusters allows the relative ages of the clusters to be determined with a mean precision of 8.4 per cent, and down to 6 per cent for individual objects. We find that the mean age of our LMC cluster ensemble is identical to the mean age of the oldest metal-poor clusters in the Milky Way halo to 0.2 ± 0.4 Gyr. This provides the most sensitive test to date of the synchronicity of the earliest epoch of globular cluster formation in two independent galaxies. Horizontal branch magnitudes and subdwarf fitting to the main sequence allow us to determine distance estimates for each cluster and examine their geometric distribution in the LMC. Using two different methods, we find an average distance to the LMC of 18.52 ± 0.05.
Shiva and Shakti: Presumed Proto-Galactic Fragments in the Inner Milky WaySérgio Sacani
Using Gaia Data Release 3 astrometry and spectroscopy, we study two new substructures in the orbit–metallicity space of the inner Milky Way: Shakti and Shiva. They were identified as two confined, high-contrast overdensities in the (Lz, E) distribution of bright (G < 16) and metal-poor (−2.5<[M/H]<−1.0) stars. Both have stellar masses of Må107Me, and are distributed on prograde orbits inside the solar circle in the Galaxy. Both structures have an orbit-space distribution that points toward an accreted origin; however, their abundance patterns—from APOGEE—are such that are conventionally attributed to an in situ population. These seemingly contradictory diagnostics could be reconciled if we interpret the abundances [Mg/Fe], [Al/Fe], [Mg/Mn] versus [Fe/H] distribution of their member stars merely as a sign of rapid enrichment. This would then suggest one of two scenarios. Either these prograde substructures were created by some form of resonant orbit trapping of the field stars by the rotating bar; a plausible scenario proposed by Dillamore et al. Or, Shakti and Shiva were protogalactic fragments that formed stars rapidly and coalesced early, akin to the constituents of the poor old heart of the Milky Way, just less deep in the Galactic potential and still discernible in orbit space.
Formation of low mass protostars and their circumstellar disksSérgio Sacani
Understanding circumstellar disks is of prime importance in astrophysics, however, their birth process remains poorly constrained due to observational and numerical challenges. Recent numerical works have shown that the small-scale physics, often wrapped into a sub-grid model, play a crucial role in disk formation and evolution. This calls for a combined approach in which both the protostar and circumstellar disk are studied in concert. Aims. We aim to elucidate the small scale physics and constrain sub-grid parameters commonly chosen in the literature by resolving the star-disk interaction. Methods. We carry out a set of very high resolution 3D radiative-hydrodynamics simulations that self-consistently describe the collapse of a turbulent dense molecular cloud core to stellar densities. We study the birth of the protostar, the circumstellar disk, and its early evolution (< 6 yr after protostellar formation). Results. Following the second gravitational collapse, the nascent protostar quickly reaches breakup velocity and sheds its surface material, thus forming a hot (∼ 103 K), dense, and highly flared circumstellar disk. The protostar is embedded within the disk, such that material can flow without crossing any shock fronts. The circumstellar disk mass quickly exceeds that of the protostar, and its kinematics are dominated by self-gravity. Accretion onto the disk is highly anisotropic, and accretion onto the protostar mainly occurs through material that slides on the disk surface. The polar mass flux is negligible in comparison. The radiative behavior also displays a strong anisotropy, as the polar accretion shock is shown to be supercritical whereas its equatorial counterpart is subcritical. We also f ind a remarkable convergence of our results with respect to initial conditions. Conclusions. These results reveal the structure and kinematics in the smallest spatial scales relevant to protostellar and circumstellar disk evolution. They can be used to describe accretion onto regions commonly described by sub-grid models in simulations studying larger scale physics.
X-Ray Properties of NGC 253ʼs Starburst-driven OutflowSérgio Sacani
We analyze image and spectral data from ≈365 ks of observations from the Chandra X-ray Observatory of the
nearby, edge-on starburst galaxy NGC 253 to constrain properties of the hot phase of the outflow. We focus our
analysis on the −1.1 to +0.63 kpc region of the outflow and define several regions for spectral extraction where we
determine best-fit temperatures and metal abundances. We find that the temperatures and electron densities peak in
the central ∼250 pc region of the outflow and decrease with distance. These temperature and density profiles are in
disagreement with an adiabatic spherically expanding starburst wind model and suggest the presence of additional
physics such as mass loading and nonspherical outflow geometry. Our derived temperatures and densities yield
cooling times in the nuclear region of a few million years, which may imply that the hot gas can undergo bulk
radiative cooling as it escapes along the minor axis. Our metal abundances of O, Ne, Mg, Si, S, and Fe all peak in
the central region and decrease with distance along the outflow, with the exception of Ne, which maintains a flat
distribution. The metal abundances indicate significant dilution outside of the starburst region. We also find
estimates of the mass outflow rates, which are 2.8 Me yr−1 in the northern outflow and 3.2 Me yr−1 in the southern
outflow. Additionally, we detect emission from charge exchange and find it makes a significant contribution (20%–
42%) to the total broadband (0.5–7 keV) X-ray emission in the central and southern regions of the outflow.
A measurement of_the_black_hole_mass_in_ngc_1097_using_almaSérgio Sacani
Artigo descreve a maneira como os astrônomos usaram pela primeira vez o ALMA para medir a massa de um buraco negro supermassivo no interior de uma galáxias espiral barrada.
Alma observations of_feeding_and_feedback_in_nearby_seyfert_galaxies_outflow_...Sérgio Sacani
ALMA observations of the Seyfert 2 galaxy NGC 1433 reveal a nuclear gaseous spiral structure within a nuclear ring encircling a nuclear stellar bar. Near the nucleus, there is intense high-velocity CO emission interpreted as an AGN-driven molecular outflow. The outflow involves a molecular mass of 3.6 million solar masses and a flow rate of about 7 solar masses per year. Continuum emission at the center is likely thermal dust emission from a molecular torus expected in this Seyfert 2 galaxy. The observations probe gas dynamics within 24 parsecs of the active galactic nucleus.
The Gaia-ESO Survey: Empirical estimates of stellar ages from lithium equival...Sérgio Sacani
We present an empirical model of age-dependent photospheric lithium depletion, calibrated using a large, homogeneouslyanalysed sample of 6200 stars in 52 open clusters, with ages from 2–6000Myr and −0.3 < [Fe/H] < 0.2, observed in the
Gaia-ESO spectroscopic survey. The model is used to obtain age estimates and posterior age probability distributions from
measurements of the Li I 6708Å equivalent width for individual (pre) main sequence stars with 3000 < Teff/K < 6500,
a domain where age determination from the HR diagram is either insensitive or highly model-dependent. In the best cases,
precisions of 0.1 dex in log age are achievable; even higher precision can be obtained for coeval groups and associations where
the individual age probabilities of their members can be combined. The method is validated on a sample of exoplanet-hosting
young stars, finding agreement with claimed young ages for some, but not others. We obtain better than 10 per cent precision
in age, and excellent agreement with published ages, for seven well-studied young moving groups. The derived ages for young
clusters (< 1 Gyr) in our sample are also in good agreement with their training ages, and consistent with several published,
model-insensitive lithium depletion boundary ages. For older clusters there remain systematic age errors that could be as large
as a factor of two. There is no evidence to link these errors to any strong systematic metallicity dependence of (pre) main
sequence lithium depletion, at least in the range −0.29 < [Fe/H] < 0.18. Our methods and model are provided as software –
"Empirical AGes from Lithium Equivalent widthS" (EAGLES).
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
Age of Jupiter inferred from the distinct genetics and formation times of met...Sérgio Sacani
The age of Jupiter, the largest planet in our Solar System, is still
unknown. Gas-giant planet formation likely involved the growth
of large solid cores, followed by the accumulation of gas onto
these cores. Thus, the gas-giant cores must have formed before
dissipation of the solar nebula, which likely occurred within less
than 10 My after Solar System formation. Although such rapid
accretion of the gas-giant cores has successfully been modeled,
until now it has not been possible to date their formation. Here,
using molybdenum and tungsten isotope measurements on iron
meteorites, we demonstrate that meteorites derive from two
genetically distinct nebular reservoirs that coexisted and remained
spatially separated between ∼1My and ∼3–4My after Solar System
formation. The most plausible mechanism for this efficient separation
is the formation of Jupiter, opening a gap in the disk and
preventing the exchange of material between the two reservoirs.
As such, our results indicate that Jupiter’s core grew to ∼20 Earth
masses within <1 My, followed by amore protracted growth to ∼50
Earth masses until at least ∼3–4 My after Solar System formation.
Thus, Jupiter is the oldest planet of the Solar System, and its solid
core formed well before the solar nebula gas dissipated, consistent
with the core accretion model for giant planet formation.
3D stellar evolution: hydrodynamic simulations of a complete burning phase in...Sérgio Sacani
Our knowledge of stellar evolution is driven by one-dimensional (1D) simulations. 1D models, however, are severely limited by uncertainties on the exact behaviour of many multidimensional phenomena occurring inside stars, affecting their structure and e volution. Recent adv ances in computing resources have allowed small sections of a star to be reproduced with multi-D hydrodynamic models, with an unprecedented degree of detail and realism. In this work, we present a set of 3D simulations of a conv ectiv e neon-burning shell in a 20 M star run for the first time continuously from its early development through to complete fuel exhaustion, using unaltered input conditions from a 321D-guided 1D stellar model. These simulations help answer some open questions in stellar physics. In particular, they show that conv ectiv e re gions do not grow indefinitely due to entrainment of fresh material, but fuel consumption pre v ails o v er entrainment, so when fuel is e xhausted conv ection also starts decaying. Our results show convergence between the multi-D simulations and the new 321D-guided 1D model, concerning the amount of conv ectiv e boundary mixing to include in stellar models. The size of the conv ectiv e zones in a star strongly affects its structure and e volution; thus, re vising their modelling in 1D will have important implications for the life and fate of stars. This will thus affect theoretical predictions related to nucleosynthesis, supernova explosions, and compact remnants.
Hot Earth or Young Venus? A nearby transiting rocky planet mysterySérgio Sacani
Venus and Earth provide astonishingly different views of the evolution of a rocky planet, raising the question of why these two rock y worlds evolv ed so differently. The recently disco v ered transiting Super-Earth LP 890-9c (TOI-4306c, SPECULOOS-2c) is a key to the question. It circles a nearby M6V star in 8.46 d. LP890-9c receives similar flux as modern Earth, which puts it very close to the inner edge of the Habitable Zone (HZ), where models differ strongly in their prediction of how long rocky planets can hold onto their water. We model the atmosphere of a hot LP890-9c at the inner edge of the HZ, where the planet could sustain several very different environments. The resulting transmission spectra differ considerably between a hot, wet exo-Earth, a steamy planet caught in a runaway greenhouse, and an exo-Venus. Distinguishing these scenarios from the planet’s spectra will provide critical new insights into the evolution of hot terrestrial planets into exo-Venus. Our model and spectra are available online as a tool to plan observations. They show that observing LP890-9c can provide key insights into the evolution of a rocky planet at the inner edge of the HZ as well as the long-term future of Earth.
The colision between_the_milky_way_and_andromedaSérgio Sacani
The document summarizes a simulation of the future collision between the Milky Way and Andromeda galaxies. It finds that given current observational constraints on their distance, velocity, and masses:
1) The Milky Way and Andromeda are likely to collide in a few billion years, within the lifetime of the Sun.
2) During the interaction, there is a chance the Sun could be pulled into an extended tidal tail between the galaxies.
3) Eventually, after the merger is complete, the Sun would most likely be scattered to the outer halo of the merged galaxy at a distance over 30 kpc.
The fornax deep_survey_with_vst_i_the_extended_and_diffuse_stellar_halo_of_ng...Sérgio Sacani
We have started a new deep, multi-imaging survey of the Fornax cluster, dubbed Fornax Deep
Survey (FDS), at the VLT Survey Telescope. In this paper we present the deep photometry inside
two square degrees around the bright galaxy NGC 1399 in the core of the cluster. We found that
the core of the Fornax cluster is characterised by a very extended and diffuse envelope surrounding
the luminous galaxy NGC 1399: we map the surface brightness out to 33 arcmin (∼ 192 kpc)
from the galaxy center and down to μg ∼ 31 mag arcsec−2 in the g band. The deep photometry
allows us to detect a faint stellar bridge in the intracluster region on the west side of NGC 1399
and towards NGC 1387. By analyzing the integrated colors of this feature, we argue that it
could be due to the ongoing interaction between the two galaxies, where the outer envelope of
NGC 1387 on its east side is stripped away. By fitting the light profile, we found that exists a
physical break radius in the total light distribution at R = 10 arcmin (∼ 58 kpc) that sets the
transition region between the bright central galaxy and the outer exponential halo, and that the
stellar halo contributes for 60% of the total light of the galaxy (Sec. 3.5). We discuss the main
implications of this work on the build-up of the stellar halo at the center of the Fornax cluster.
By comparing with the numerical simulations of the stellar halo formation for the most massive
BCGs (i.e. 13 < logM200/M⊙ < 14), we find that the observed stellar halo mass fraction is
consistent with a halo formed through the multiple accretion of progenitors with stellar mass in
the range 108 − 1011 M⊙. This might suggest that the halo of NGC 1399 has also gone through
a major merging event. The absence of a significant number of luminous stellar streams and
tidal tails out to 192 kpc suggests that the epoch of this strong interaction goes back to an early
formation epoch. Therefore, differently from the Virgo cluster, the extended stellar halo around
NGC 1399 is characterised by a more diffuse and well-mixed component, including the ICL.
This document presents an analysis of metallicity gradients in the Milky Way disk as observed by the SEGUE survey. The key findings are:
1) The radial metallicity gradient (change in [Fe/H] with Galactic radius R) becomes flatter at heights above the plane (|Z|) greater than 1 kpc.
2) The median metallicity at large |Z| is consistent with outer disk open clusters, which also exhibit a flat radial gradient of [Fe/H] ∼ -0.5.
3) A flat metallicity gradient at high |Z| has implications for models of thick disk formation, as different formation scenarios predict different metallicity patterns in the thick disk.
This document summarizes the analysis of periodic variable stars in the open cluster NGC 3766 based on a 7-year monitoring campaign. The authors detected a new class of 36 variable stars located between the instability strips for slowly pulsating B stars and delta Scuti stars, where no variability was previously predicted. The majority of these new variables have periods between 0.1-0.7 days and amplitudes of 1-4 millimagnitudes. The properties of this new class are discussed and the authors argue they are likely pulsating variables sustained by stellar rotation. Additionally, the authors identify other periodic variables such as eclipsing binaries, slowly pulsating B stars, delta Scuti stars, and gamma Doradus candidates.
Similar to Modelling element abundances_in_semi_analytic_models_of_galaxy_formation (20)
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆Sérgio Sacani
Context. The early-type galaxy SDSS J133519.91+072807.4 (hereafter SDSS1335+0728), which had exhibited no prior optical variations during the preceding two decades, began showing significant nuclear variability in the Zwicky Transient Facility (ZTF) alert stream from December 2019 (as ZTF19acnskyy). This variability behaviour, coupled with the host-galaxy properties, suggests that SDSS1335+0728 hosts a ∼ 106M⊙ black hole (BH) that is currently in the process of ‘turning on’. Aims. We present a multi-wavelength photometric analysis and spectroscopic follow-up performed with the aim of better understanding the origin of the nuclear variations detected in SDSS1335+0728. Methods. We used archival photometry (from WISE, 2MASS, SDSS, GALEX, eROSITA) and spectroscopic data (from SDSS and LAMOST) to study the state of SDSS1335+0728 prior to December 2019, and new observations from Swift, SOAR/Goodman, VLT/X-shooter, and Keck/LRIS taken after its turn-on to characterise its current state. We analysed the variability of SDSS1335+0728 in the X-ray/UV/optical/mid-infrared range, modelled its spectral energy distribution prior to and after December 2019, and studied the evolution of its UV/optical spectra. Results. From our multi-wavelength photometric analysis, we find that: (a) since 2021, the UV flux (from Swift/UVOT observations) is four times brighter than the flux reported by GALEX in 2004; (b) since June 2022, the mid-infrared flux has risen more than two times, and the W1−W2 WISE colour has become redder; and (c) since February 2024, the source has begun showing X-ray emission. From our spectroscopic follow-up, we see that (i) the narrow emission line ratios are now consistent with a more energetic ionising continuum; (ii) broad emission lines are not detected; and (iii) the [OIII] line increased its flux ∼ 3.6 years after the first ZTF alert, which implies a relatively compact narrow-line-emitting region. Conclusions. We conclude that the variations observed in SDSS1335+0728 could be either explained by a ∼ 106M⊙ AGN that is just turning on or by an exotic tidal disruption event (TDE). If the former is true, SDSS1335+0728 is one of the strongest cases of an AGNobserved in the process of activating. If the latter were found to be the case, it would correspond to the longest and faintest TDE ever observed (or another class of still unknown nuclear transient). Future observations of SDSS1335+0728 are crucial to further understand its behaviour. Key words. galaxies: active– accretion, accretion discs– galaxies: individual: SDSS J133519.91+072807.4
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...Sérgio Sacani
We present the JWST discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS
+
53.13485
−
27.82088
with a host spectroscopic redshift of
2.903
±
0.007
. The transient was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (
�
(
�
−
�
)
∼
0.9
) despite a host galaxy with low-extinction and has a high Ca II velocity (
19
,
000
±
2
,
000
km/s) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-
�
Ca-rich population. Although such an object is too red for any low-
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cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (
≲
1
�
) with
Λ
CDM. Therefore unlike low-
�
Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high-
�
truly diverge from their low-
�
counterparts, and to confirm that standardized luminosities nevertheless remain constant with redshift.
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Sérgio Sacani
Wereport the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R-band. There is a big change in the R–I spectral index by 1.0 ±0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ287 as well as the dense monitoring sample of Krakow.
Candidate young stellar objects in the S-cluster: Kinematic analysis of a sub...Sérgio Sacani
Context. The observation of several L-band emission sources in the S cluster has led to a rich discussion of their nature. However, a definitive answer to the classification of the dusty objects requires an explanation for the detection of compact Doppler-shifted Brγ emission. The ionized hydrogen in combination with the observation of mid-infrared L-band continuum emission suggests that most of these sources are embedded in a dusty envelope. These embedded sources are part of the S-cluster, and their relationship to the S-stars is still under debate. To date, the question of the origin of these two populations has been vague, although all explanations favor migration processes for the individual cluster members. Aims. This work revisits the S-cluster and its dusty members orbiting the supermassive black hole SgrA* on bound Keplerian orbits from a kinematic perspective. The aim is to explore the Keplerian parameters for patterns that might imply a nonrandom distribution of the sample. Additionally, various analytical aspects are considered to address the nature of the dusty sources. Methods. Based on the photometric analysis, we estimated the individual H−K and K−L colors for the source sample and compared the results to known cluster members. The classification revealed a noticeable contrast between the S-stars and the dusty sources. To fit the flux-density distribution, we utilized the radiative transfer code HYPERION and implemented a young stellar object Class I model. We obtained the position angle from the Keplerian fit results; additionally, we analyzed the distribution of the inclinations and the longitudes of the ascending node. Results. The colors of the dusty sources suggest a stellar nature consistent with the spectral energy distribution in the near and midinfrared domains. Furthermore, the evaporation timescales of dusty and gaseous clumps in the vicinity of SgrA* are much shorter ( 2yr) than the epochs covered by the observations (≈15yr). In addition to the strong evidence for the stellar classification of the D-sources, we also find a clear disk-like pattern following the arrangements of S-stars proposed in the literature. Furthermore, we find a global intrinsic inclination for all dusty sources of 60 ± 20◦, implying a common formation process. Conclusions. The pattern of the dusty sources manifested in the distribution of the position angles, inclinations, and longitudes of the ascending node strongly suggests two different scenarios: the main-sequence stars and the dusty stellar S-cluster sources share a common formation history or migrated with a similar formation channel in the vicinity of SgrA*. Alternatively, the gravitational influence of SgrA* in combination with a massive perturber, such as a putative intermediate mass black hole in the IRS 13 cluster, forces the dusty objects and S-stars to follow a particular orbital arrangement. Key words. stars: black holes– stars: formation– Galaxy: center– galaxies: star formation
JAMES WEBB STUDY THE MASSIVE BLACK HOLE SEEDSSérgio Sacani
The pathway(s) to seeding the massive black holes (MBHs) that exist at the heart of galaxies in the present and distant Universe remains an unsolved problem. Here we categorise, describe and quantitatively discuss the formation pathways of both light and heavy seeds. We emphasise that the most recent computational models suggest that rather than a bimodal-like mass spectrum between light and heavy seeds with light at one end and heavy at the other that instead a continuum exists. Light seeds being more ubiquitous and the heavier seeds becoming less and less abundant due the rarer environmental conditions required for their formation. We therefore examine the different mechanisms that give rise to different seed mass spectrums. We show how and why the mechanisms that produce the heaviest seeds are also among the rarest events in the Universe and are hence extremely unlikely to be the seeds for the vast majority of the MBH population. We quantify, within the limits of the current large uncertainties in the seeding processes, the expected number densities of the seed mass spectrum. We argue that light seeds must be at least 103 to 105 times more numerous than heavy seeds to explain the MBH population as a whole. Based on our current understanding of the seed population this makes heavy seeds (Mseed > 103 M⊙) a significantly more likely pathway given that heavy seeds have an abundance pattern than is close to and likely in excess of 10−4 compared to light seeds. Finally, we examine the current state-of-the-art in numerical calculations and recent observations and plot a path forward for near-future advances in both domains.
Anti-Universe And Emergent Gravity and the Dark UniverseSérgio Sacani
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional ‘dark’ gravitational force describing the ‘elastic’ response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton’s constant and the Hubble acceleration scale a0 = cH0, and provide evidence for the fact that this additional ‘dark gravity force’ explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
For the full video of this presentation, please visit: https://www.edge-ai-vision.com/2024/06/temporal-event-neural-networks-a-more-efficient-alternative-to-the-transformer-a-presentation-from-brainchip/
Chris Jones, Director of Product Management at BrainChip , presents the “Temporal Event Neural Networks: A More Efficient Alternative to the Transformer” tutorial at the May 2024 Embedded Vision Summit.
The expansion of AI services necessitates enhanced computational capabilities on edge devices. Temporal Event Neural Networks (TENNs), developed by BrainChip, represent a novel and highly efficient state-space network. TENNs demonstrate exceptional proficiency in handling multi-dimensional streaming data, facilitating advancements in object detection, action recognition, speech enhancement and language model/sequence generation. Through the utilization of polynomial-based continuous convolutions, TENNs streamline models, expedite training processes and significantly diminish memory requirements, achieving notable reductions of up to 50x in parameters and 5,000x in energy consumption compared to prevailing methodologies like transformers.
Integration with BrainChip’s Akida neuromorphic hardware IP further enhances TENNs’ capabilities, enabling the realization of highly capable, portable and passively cooled edge devices. This presentation delves into the technical innovations underlying TENNs, presents real-world benchmarks, and elucidates how this cutting-edge approach is positioned to revolutionize edge AI across diverse applications.
Fueling AI with Great Data with Airbyte WebinarZilliz
This talk will focus on how to collect data from a variety of sources, leveraging this data for RAG and other GenAI use cases, and finally charting your course to productionalization.
Monitoring and Managing Anomaly Detection on OpenShift.pdfTosin Akinosho
Monitoring and Managing Anomaly Detection on OpenShift
Overview
Dive into the world of anomaly detection on edge devices with our comprehensive hands-on tutorial. This SlideShare presentation will guide you through the entire process, from data collection and model training to edge deployment and real-time monitoring. Perfect for those looking to implement robust anomaly detection systems on resource-constrained IoT/edge devices.
Key Topics Covered
1. Introduction to Anomaly Detection
- Understand the fundamentals of anomaly detection and its importance in identifying unusual behavior or failures in systems.
2. Understanding Edge (IoT)
- Learn about edge computing and IoT, and how they enable real-time data processing and decision-making at the source.
3. What is ArgoCD?
- Discover ArgoCD, a declarative, GitOps continuous delivery tool for Kubernetes, and its role in deploying applications on edge devices.
4. Deployment Using ArgoCD for Edge Devices
- Step-by-step guide on deploying anomaly detection models on edge devices using ArgoCD.
5. Introduction to Apache Kafka and S3
- Explore Apache Kafka for real-time data streaming and Amazon S3 for scalable storage solutions.
6. Viewing Kafka Messages in the Data Lake
- Learn how to view and analyze Kafka messages stored in a data lake for better insights.
7. What is Prometheus?
- Get to know Prometheus, an open-source monitoring and alerting toolkit, and its application in monitoring edge devices.
8. Monitoring Application Metrics with Prometheus
- Detailed instructions on setting up Prometheus to monitor the performance and health of your anomaly detection system.
9. What is Camel K?
- Introduction to Camel K, a lightweight integration framework built on Apache Camel, designed for Kubernetes.
10. Configuring Camel K Integrations for Data Pipelines
- Learn how to configure Camel K for seamless data pipeline integrations in your anomaly detection workflow.
11. What is a Jupyter Notebook?
- Overview of Jupyter Notebooks, an open-source web application for creating and sharing documents with live code, equations, visualizations, and narrative text.
12. Jupyter Notebooks with Code Examples
- Hands-on examples and code snippets in Jupyter Notebooks to help you implement and test anomaly detection models.
Dandelion Hashtable: beyond billion requests per second on a commodity serverAntonios Katsarakis
This slide deck presents DLHT, a concurrent in-memory hashtable. Despite efforts to optimize hashtables, that go as far as sacrificing core functionality, state-of-the-art designs still incur multiple memory accesses per request and block request processing in three cases. First, most hashtables block while waiting for data to be retrieved from memory. Second, open-addressing designs, which represent the current state-of-the-art, either cannot free index slots on deletes or must block all requests to do so. Third, index resizes block every request until all objects are copied to the new index. Defying folklore wisdom, DLHT forgoes open-addressing and adopts a fully-featured and memory-aware closed-addressing design based on bounded cache-line-chaining. This design offers lock-free index operations and deletes that free slots instantly, (2) completes most requests with a single memory access, (3) utilizes software prefetching to hide memory latencies, and (4) employs a novel non-blocking and parallel resizing. In a commodity server and a memory-resident workload, DLHT surpasses 1.6B requests per second and provides 3.5x (12x) the throughput of the state-of-the-art closed-addressing (open-addressing) resizable hashtable on Gets (Deletes).
Trusted Execution Environment for Decentralized Process MiningLucaBarbaro3
Presentation of the paper "Trusted Execution Environment for Decentralized Process Mining" given during the CAiSE 2024 Conference in Cyprus on June 7, 2024.
5th LF Energy Power Grid Model Meet-up SlidesDanBrown980551
5th Power Grid Model Meet-up
It is with great pleasure that we extend to you an invitation to the 5th Power Grid Model Meet-up, scheduled for 6th June 2024. This event will adopt a hybrid format, allowing participants to join us either through an online Mircosoft Teams session or in person at TU/e located at Den Dolech 2, Eindhoven, Netherlands. The meet-up will be hosted by Eindhoven University of Technology (TU/e), a research university specializing in engineering science & technology.
Power Grid Model
The global energy transition is placing new and unprecedented demands on Distribution System Operators (DSOs). Alongside upgrades to grid capacity, processes such as digitization, capacity optimization, and congestion management are becoming vital for delivering reliable services.
Power Grid Model is an open source project from Linux Foundation Energy and provides a calculation engine that is increasingly essential for DSOs. It offers a standards-based foundation enabling real-time power systems analysis, simulations of electrical power grids, and sophisticated what-if analysis. In addition, it enables in-depth studies and analysis of the electrical power grid’s behavior and performance. This comprehensive model incorporates essential factors such as power generation capacity, electrical losses, voltage levels, power flows, and system stability.
Power Grid Model is currently being applied in a wide variety of use cases, including grid planning, expansion, reliability, and congestion studies. It can also help in analyzing the impact of renewable energy integration, assessing the effects of disturbances or faults, and developing strategies for grid control and optimization.
What to expect
For the upcoming meetup we are organizing, we have an exciting lineup of activities planned:
-Insightful presentations covering two practical applications of the Power Grid Model.
-An update on the latest advancements in Power Grid -Model technology during the first and second quarters of 2024.
-An interactive brainstorming session to discuss and propose new feature requests.
-An opportunity to connect with fellow Power Grid Model enthusiasts and users.
GraphRAG for Life Science to increase LLM accuracyTomaz Bratanic
GraphRAG for life science domain, where you retriever information from biomedical knowledge graphs using LLMs to increase the accuracy and performance of generated answers
Generating privacy-protected synthetic data using Secludy and MilvusZilliz
During this demo, the founders of Secludy will demonstrate how their system utilizes Milvus to store and manipulate embeddings for generating privacy-protected synthetic data. Their approach not only maintains the confidentiality of the original data but also enhances the utility and scalability of LLMs under privacy constraints. Attendees, including machine learning engineers, data scientists, and data managers, will witness first-hand how Secludy's integration with Milvus empowers organizations to harness the power of LLMs securely and efficiently.
FREE A4 Cyber Security Awareness Posters-Social Engineering part 3Data Hops
Free A4 downloadable and printable Cyber Security, Social Engineering Safety and security Training Posters . Promote security awareness in the home or workplace. Lock them Out From training providers datahops.com
Skybuffer AI: Advanced Conversational and Generative AI Solution on SAP Busin...Tatiana Kojar
Skybuffer AI, built on the robust SAP Business Technology Platform (SAP BTP), is the latest and most advanced version of our AI development, reaffirming our commitment to delivering top-tier AI solutions. Skybuffer AI harnesses all the innovative capabilities of the SAP BTP in the AI domain, from Conversational AI to cutting-edge Generative AI and Retrieval-Augmented Generation (RAG). It also helps SAP customers safeguard their investments into SAP Conversational AI and ensure a seamless, one-click transition to SAP Business AI.
With Skybuffer AI, various AI models can be integrated into a single communication channel such as Microsoft Teams. This integration empowers business users with insights drawn from SAP backend systems, enterprise documents, and the expansive knowledge of Generative AI. And the best part of it is that it is all managed through our intuitive no-code Action Server interface, requiring no extensive coding knowledge and making the advanced AI accessible to more users.
Programming Foundation Models with DSPy - Meetup SlidesZilliz
Prompting language models is hard, while programming language models is easy. In this talk, I will discuss the state-of-the-art framework DSPy for programming foundation models with its powerful optimizers and runtime constraint system.
Salesforce Integration for Bonterra Impact Management (fka Social Solutions A...Jeffrey Haguewood
Sidekick Solutions uses Bonterra Impact Management (fka Social Solutions Apricot) and automation solutions to integrate data for business workflows.
We believe integration and automation are essential to user experience and the promise of efficient work through technology. Automation is the critical ingredient to realizing that full vision. We develop integration products and services for Bonterra Case Management software to support the deployment of automations for a variety of use cases.
This video focuses on integration of Salesforce with Bonterra Impact Management.
Interested in deploying an integration with Salesforce for Bonterra Impact Management? Contact us at sales@sidekicksolutionsllc.com to discuss next steps.
How to Interpret Trends in the Kalyan Rajdhani Mix Chart.pdfChart Kalyan
A Mix Chart displays historical data of numbers in a graphical or tabular form. The Kalyan Rajdhani Mix Chart specifically shows the results of a sequence of numbers over different periods.
Building Production Ready Search Pipelines with Spark and MilvusZilliz
Spark is the widely used ETL tool for processing, indexing and ingesting data to serving stack for search. Milvus is the production-ready open-source vector database. In this talk we will show how to use Spark to process unstructured data to extract vector representations, and push the vectors to Milvus vector database for search serving.
Ivanti’s Patch Tuesday breakdown goes beyond patching your applications and brings you the intelligence and guidance needed to prioritize where to focus your attention first. Catch early analysis on our Ivanti blog, then join industry expert Chris Goettl for the Patch Tuesday Webinar Event. There we’ll do a deep dive into each of the bulletins and give guidance on the risks associated with the newly-identified vulnerabilities.
Main news related to the CCS TSI 2023 (2023/1695)Jakub Marek
An English 🇬🇧 translation of a presentation to the speech I gave about the main changes brought by CCS TSI 2023 at the biggest Czech conference on Communications and signalling systems on Railways, which was held in Clarion Hotel Olomouc from 7th to 9th November 2023 (konferenceszt.cz). Attended by around 500 participants and 200 on-line followers.
The original Czech 🇨🇿 version of the presentation can be found here: https://www.slideshare.net/slideshow/hlavni-novinky-souvisejici-s-ccs-tsi-2023-2023-1695/269688092 .
The videorecording (in Czech) from the presentation is available here: https://youtu.be/WzjJWm4IyPk?si=SImb06tuXGb30BEH .
Modelling element abundances_in_semi_analytic_models_of_galaxy_formation
1. arXiv:1305.7231v1[astro-ph.CO]30May2013
Mon. Not. R. Astron. Soc. 000, 000–000 (0000) Printed 3 June 2013 (MN LATEX style file v2.2)
Modelling Element Abundances in Semi-analytic Models of
Galaxy Formation
Robert M. Yates1⋆
, Bruno Henriques1
, Peter A. Thomas2
, Guinevere Kauffmann1
,
Jonas Johansson1
& Simon D. M. White1
1 Max Planck Institut f¨ur Astrophysik, Karl-Schwarzschild-Str. 1, 85741, Garching, Germany
2 Astronomy Centre, University of Sussex, Falmer, Brighton BN1 9QH, UK
Accepted ??. Received ??; in original form ??
ABSTRACT
We update the treatment of chemical evolution in the Munich semi-analytic model, L-
Galaxies. Our new implementation includes delayed enrichment from stellar winds,
supernovæ type II (SNe-II) and supernovæ type Ia (SNe-Ia), as well as metallicity-
dependent yields and a reformulation of the associated supernova feedback. Two differ-
ent sets of SN-II yields and three different SN-Ia delay-time distributions (DTDs) are
considered, and eleven heavy elements (including O, Mg and Fe) are self-consistently
tracked. We compare the results of this new implementation with data on a) local,
star-forming galaxies, b) Milky Way disc G dwarfs, and c) local, elliptical galaxies.
We find that the z = 0 gas-phase mass-metallicity relation is very well reproduced
for all forms of DTD considered, as is the [Fe/H] distribution in the Milky Way disc.
The [O/Fe] distribution in the Milky Way disc is best reproduced when using a DTD
with 50 per cent of SNe-Ia exploding within ∼ 400 Myrs. Positive slopes in the
mass-[α/Fe] relations of local ellipticals are also obtained when using a DTD with
such a minor ‘prompt’ component. Alternatively, metal-rich winds that drive light α
elements directly out into the circumgalactic medium also produce positive slopes for
all forms of DTD and SN-II yields considered. Overall, we find that the best model
for matching the wide range of observational data considered here should include a
power-law SN-Ia DTD, SN-II yields that take account of prior mass loss through stellar
winds, and some direct ejection of light α elements out of galaxies.
Key words: Galaxy: abundances – Galaxies: abundances – Galaxies: evolution –
Supernovæ: general – Methods: analytical
1 INTRODUCTION
Significant progress has been made in the field of galac-
tic chemical evolution (GCE) since the first postulation of
stellar nucleosynthesis by Arthur Eddington in the 1920s
(Eddington 1920). The first techniques to determine ele-
ment abundances in both gas (e.g. Aller 1942) and stars (e.g.
Chamberlain & Aller 1951) were developed, and the theory
of stellar nucleosynthesis was given a more formal footing
by Burbidge et al. (1957). Later, more sophisticated studies
of GCE were stimulated by the celebrated review by Beat-
rice Tinsley (Tinsley 1980). Now, it has been determined
that a galaxy’s metallicity is related to its luminosity (e.g.
Lequeux et al. 1979), age (e.g. Edvardsson et al. 1993, but
see e.g. Friel 1995), and stellar mass (e.g. Tremonti et al.
⋆ Email: robyates@mpa-garching.mpg.de
2004), and that different types of stars contribute to GCE
in different ways (e.g. Salaris & Cassisi 2005).
However, many questions relating to the cosmic abun-
dances of heavy elements still remain. For example, it is
still unclear what exact role different types of supernovæ
(SNe) and stellar winds play in the chemical enrichment
of galaxies (e.g. McWilliam 1997), what the shape and
universality of the stellar initial mass function (IMF) is
(e.g. Bastian, Covey & Meyer 2010), how best to model the
metal yields produced in stars (e.g. Romano et al. 2010),
and what the progenitors and delay times of SNe-Ia are
(e.g. Maoz & Mannucci 2012). These are important ques-
tions for us to address, as the chemical evolution of galax-
ies plays a key part in the evolution of galaxies in gen-
eral; the presence of metals affects the cooling of gas (e.g.
Sutherland & Dopita 1993), the formation of stars (e.g.
Walch et al. 2011), stellar evolution (e.g. Salaris & Cassisi
c 0000 RAS
2. 2 Yates et al.
2005), and the yields of newly synthesised metals (e.g.
Woosley & Weaver 1995) which are released into the inter-
stellar medium (ISM), circumgalactic medium (CGM) and
even the intergalactic medium (IGM).
Aside from the ongoing observational studies into
these questions, galaxy evolution models incorporating
sophisticated GCE modelling also provide an oppor-
tunity to further constrain the chemical evolution of
galaxies. Many previous works have focused on re-
producing the chemical signitures found in the solar
neighbourhood (e.g. Tinsley 1980; Matteucci & Greggio
1986; Matteucci 1986; Thomas, Greggio & Bender
1998; Fran¸cois et al. 2004; De Rossi et al. 2009;
Calura & Menci 2009; Calura et al. 2010; Romano et al.
2010; Tissera, White & Scannapieco 2012; Pilkington et al.
2012; Calura et al. 2012), chiefly in order to constrain
the contributions from different types of SNe and stel-
lar winds. Many others have focused on the chemical
properties of local elliptical galaxies (e.g. Matteucci 1994;
Thomas & Kauffmann 1999; Thomas, Greggio & Bender
1999; Pipino & Matteucci 2004; Nagashima et al. 2005b;
Pipino et al. 2009a,b; Calura & Menci 2009; Arrigoni et al.
2010a; Calura & Menci 2011; Pipino & Matteucci 2011),
chiefly to try to reconcile the observed positive slope in
the relation between stellar mass (M∗) and α enhancement
([α/Fe]) with our theoretical understanding of metal
production and galaxy formation.
The aim of this work is to address both of these issues,
using a new implementation of detailed chemical enrich-
ment in the Munich semi-analytic model of galaxy forma-
tion. We investigate if the chemical properties of Milky Way
(MW) disc stars and local elliptical galaxies can be simulta-
neously obtained with a self-consistent model which assumes
a ΛCDM hierarchical merging scenario and varied star for-
mation histories (SFHs). We also compare different SNe-II
yield sets and SN-Ia delay-time distributions (DTDs), to see
which allow us to best match the observational data consid-
ered.
This paper is structured as follows: in §2 we give
a general outline of the Munich semi-analytic model, L-
Galaxies. In §3 we describe the stellar yields, lifetimes and
IMF used as inputs to our model. In §4 we describe the
basic equations required to model GCE and discuss the SN-
Ia DTD. In §5 we explain how this GCE model is imple-
mented into the larger semi-analytic model and review the
key physical processes governing the distribution of metals
throughout galaxies. In §6 we discuss our model results for
the chemical composition of a) local, star-forming galaxies,
b) the G dwarfs of the MW disc, and c) the stellar compo-
nents of local ellipticals, and compare these results to the
latest observations. We conclude our work in §7.
2 THE SEMI-ANALYTIC MODEL
L-Galaxies (Springel et al. 2001;
De Lucia, Kauffmann & White 2004; Springel et al. 2005;
Croton et al. 2006; De Lucia & Blaizot 2007; Guo et al.
2011, 2013; Henriques et al. 2013) is a semi-analytic model
of galaxy evolution which extends the methods set out
in White & Frenk (1991); Kauffmann, White & Guideroni
(1993); Kauffmann et al. (1999) so that the model can be
run on subhalo trees built from DM N-body simulations
such as the Millennium (Springel et al. 2005). Galaxy evo-
lution is governed by the transfer of mass among the various
components of a galaxy (disc stars, bulge stars, halo stars,
cold gas, hot gas, central black hole, and ejecta reservoir),
according to physical laws motivated by observations and
simulations. L-Galaxies is currently able to reproduce the
large-scale clustering of galaxies, the Tully-Fisher relation,
and the optical colours, stellar mass function and gas-phase
mass-metallicity relation observed in the local Universe.
The model can also reproduce the abundance of galaxies
as a function of stellar mass or luminosity out to z = 3.
Analytical treatments of gas stripping and tidal disruption
of satellites, as well as SN and AGN feedback are included
(see Guo et al. 2011). The processes already included in
L-Galaxies that are of most relevance to this work are
reviewed briefly in §5.3.
Prior to this work, L-Galaxies included a simple GCE
implementation. A fixed metal yield of 0.03 · ∆M∗ was as-
sumed to be ejected into the ISM immediately after a star
formation event, where ∆M∗ is the mass of stars formed
at that time. A further 40 per cent of ∆M∗ was assumed
to return immediately to the gas phase as H and He. Such
an ‘instantaneous recycling approximation’ is often used in
galaxy formation models for its simplicity, but does not ad-
equately describe the delayed enrichment of metals, partic-
ularly from long-lived low- and intermediate-mass stars and
SNe-Ia. Previously, L-Galaxies also did not consider indi-
vidual chemical elements, but instead tracked only the total
metal mass in each galaxy component. The tracking of in-
dividual elements allows us to compare with more detailed
observational data on the chemical composition of the Milky
Way and other galaxies (see §6). For example, the ratio of
α elements to iron is believed to be a good indicator of the
star formation timescale. A comparison of [α/Fe] between
real galaxies and model galaxies with known star formation
histories will allow us to test this. Also, in future, tracking
individual elements will provide a more realistic treatment
of gas cooling, which depends not only on the total metal-
licity, but also on the relative abundance of different heavy
elements, as well as the ultraviolet background radiation.
The model parameters we use in this paper are identical
to those in Guo et al. (2011), with the exception of the ‘halo-
velocity-dependent SN energy efficiency’, ǫh, which we have
increased in order to maintain the same total SN feedback
energy that was used previously (see §5.3.3).
3 GCE INGREDIENTS
In order to model the chemical evolution of galaxies, we first
need to know the total mass of heavy elements liberated
from stars at any given time. To do this, we need to know
a) how many stars eject metals at that time, and b) how
much of each element they eject. The former is given by the
assumed stellar lifetimes, the IMF and the SFHs of galaxies.
The latter is given by the stellar yields, obtained from stellar
evolution models.
The yields, as well as depending on the initial mass
(and metallicity) of the star, also depend on the mode
of ejection. We consider three modes in this work; stellar
winds from low- and intermediate-mass stars during their
c 0000 RAS, MNRAS 000, 000–000
3. Modelling element abundances 3
thermally-pulsing asymptotic giant branch phase (TP-AGB,
or simply AGB phase), SNe-Ia from some intermediate-
mass binary systems, and the SN-II explosions of mas-
sive stars. Each of these three modes releases a different
set of heavy elements at different times. Long-lived stars
of mass 0.85 M/M⊙ 7 release mainly He, C and
N. SNe-Ia produce and eject mainly Fe and other iron-
peak elements, whether they originate from single degen-
erate binaries (Whelan & Iben 1973), double degenerate
binaries (Webbink 1984; Iben & Tutukov 1984), or other-
wise (e.g. the binary progenitors of double-detonation, sub-
Chandrasekhar-mass explosions, see Ruiter et al. 2011). Fi-
nally, short-lived stars of mass 7M⊙ explode as core-
collapse SNe-II, ejecting chiefly α elements (e.g. O, Ne, Mg,
Si, S and Ca).
We note here that we only consider eleven chemical el-
ements in our GCE model, namely, H, He, C, N, O, Ne, Mg,
Si, S, Ca and Fe, as these elements are included in all of the
yield sets we consider.
The following sub-sections outline in more detail these
key ingredients for galactic chemical enrichment. The SFHs
of galaxies are tracked self-consistently in our semi-analytic
model and are discussed in §5.1.
3.1 The IMF
The IMF, φ(M), is a probability density function, which
tells us the fraction of stars in a 1M⊙ simple stellar popula-
tion (SSP) that are within a given mass range. It is obtained
from the observable present day mass function (PDMF) of
field stars in the Milky Way, or from PDMF indicators in
extragalactic regions. In this work, we assume that the IMF
is the same in all regions of space and does not evolve with
time. There are, however, currently conflicting conclusions in
the literature as to its universality (e.g. Weidner & Kroupa
2006; Elmegreen 2006; Bastian, Covey & Meyer 2010;
van Dokkum & Conroy 2010; Gunawardhana et al.
2011; Fumagalli, Da Silva & Krumholz 2011;
Conroy & van Dokkum 2012b).
The IMF used in this work is taken from Chabrier
(2003). This version is commonly used in chemical enrich-
ment models, and is already utilised in L-Galaxies via the
stellar population synthesis models of Bruzual & Charlot
(2003); Maraston (2005). It’s use therefore provides both a
good comparison to other works and self-consistency within
the code. The Chabrier IMF is given analytically as
φ(M) =
AφM−1
e−(log M−log Mc)2
/2σ2
if M 1M⊙
BφM−2.3
if M > 1M⊙
,
(1)
where Mc = 0.079M⊙ and σ = 0.69. The values of the coef-
ficients Aφ and Bφ are determined by requiring that a) the
overall function is continuous, and b) the IMF by mass is
normalised to 1M⊙ over the full mass range of stars consid-
ered;
Mmax
Mmin
Mφ(M)dM = 1M⊙ , (2)
where Mmin = 0.1M⊙. When assuming Mmax = 120M⊙,
Figure 1. The lifetimes of stars as a function of initial
mass, for five different initial metallicities, as predicted by
Portinari, Chiosi & Bressan (1998).
as we do in this work, the coefficients in Eqn. 1 are Aφ =
0.842984 and Bφ = 0.235480.
Once normalised to the total mass of the SSP, Eqn. 1
can be integrated over a certain mass range to tell us the
number density (n = N/V ) of stars in that mass range. As-
suming that the IMF is the same everywhere, this is equiv-
alent to the number of stars in a 1M⊙ SSP in a given mass
range1
. This integrated, normalised IMF has units of 1/M⊙.
The Chabrier IMF predicts fewer stars of mass < 1M⊙
than the Salpeter (1955) IMF, and does so with a smoother
transition than the multi-segment power-law Kroupa (2001)
IMF. At masses above 1M⊙, it has the same slope as the
Kroupa IMF (an exponent of -2.3 in linear mass units, rather
than the -2.35 used for the Salpeter IMF).
3.2 Stellar lifetimes
We adopt the metallicity-dependent lifetimes tabulated by
Portinari, Chiosi & Bressan (1998, hereafter P98), kindly
provided by R. Wiersma (priv. comm.). These account for
stars in the mass range 0.6 M/M⊙ 120, and five differ-
ent initial metallicities, from 0.0004 to 0.05 (where metallic-
ity is the fraction MZ/M here). The same study also pro-
vided SN-II yield tables, which we also use (see §3.5).
The lifetimes for different initial metallicities are plot-
ted as a function of mass in Fig. 1. Within the metallicity
range shown, the most massive stars (∼ 120M⊙) live for
up to ∼ 3.3 Myrs, depending on their initial metallicity,
while the smallest stars that shed material during their lives
(∼ 0.85M⊙) live for ∼ 10 to 21 Gyrs. Stars of ∼ 1M⊙ can live
from ∼ 6 to 10 Gyrs according to these lifetime tables, im-
plying that some G V stars (also known as G dwarfs) would
not live for more than a Hubble time. The implications of
this are briefly discussed in §6.2.
1 Note that other authors, such as Lia, Portinari & Carraro
(2002) and Arrigoni et al. (2010a), choose to define the IMF as
the mass of stars in a 1M⊙ SSP, Φ(M). This is related to the
IMF defined in this work, φ(M), by Φ(M) = Mφ(M).
c 0000 RAS, MNRAS 000, 000–000
4. 4 Yates et al.
Figure 2. Mass released by AGB winds from the Marigo (2001) yield tables. Points indicate values from the yield tables. Solid lines
indicate the interpolation used between these points. Dashed lines indicate extrapolations beyond the masses originally modelled. Top
left: The mass of metals ejected as a function of mass, for three different initial metallicities. Top right: The total baryonic mass ejected
as a function of mass, for three different initial metallicities. Bottom left: The mass of each element ejected as a function of mass, for
stars of Z0 = 0.004. Bottom right: Same as bottom left, for stars of Z0 = 0.019.
3.3 AGB wind yields
We adopt the metallicity-dependent yield tables of Marigo
(2001, hereafter M01) for low- and intermediate mass stars,
which eject their metals predominantly through stellar
winds during their AGB phase.2
The SN-II yield tables of
P98, which we also use, form a complete set with those of
M01 for AGB winds. They are both based on the same
Padova evolutionary tracks and do not require a large in-
terpolation between them, as the AGB yields consider stars
up to 5M⊙ and the SN-II yields consider down to 7M⊙.3
In
this work, we consider the ejecta from AGB winds to occur
at the end of a star’s lifetime.
Fig. 2 shows the ejected mass of metals (top left panel),
total baryons (top right panel), and individual elements
(bottom two panels) from AGB stars as a function of initial
mass. This is different from the yield, as it includes both
the mass that passes through the stars unprocessed and any
2 Total yields from the RGB and AGB phases together are in-
cluded in the M01 tables. For simplicity, we refer to these as ‘AGB
wind’ yields hereafter.
3 We note that it is also possible to link the M01 AGB yields
to the P98 SN-II yields at 6M⊙, by including the P98 yields for
electron-capture SNe (see P98,§4.2). Doing this makes a negliga-
ble difference to the results discussed in this work.
newly synthesised material.4
The element abundances of the
Sun from Asplund et al. (2009) are used to scale the ampli-
tudes of the curves in Fig. 2.
We note that no elements heavier than oxygen present
in the wind have been synthesised or destroyed in the AGB
stars, but have instead been formed in previous generations
of stars and pass through the AGB stars unprocessed. We
have extrapolated the AGB wind yields from 5M⊙ to 7M⊙,
so that they meet with the SN-II yields used. The exact
position of this interface within the region 5 < M/M⊙ < 8
does not significantly affect our results.
3.4 SN-Ia yields
As with many other chemical enrichment models, we adopt
the spherically symmetric ‘W7’ model for our SN-Ia ex-
plosive yields, originally tabulated by Nomoto et al. (1984).
We use a more recent iteration, by Thielemann et al. (2003,
hereafter T03). These tables provide the synthesised mass of
4 The element ‘yield’ of a star is defined as the mass of that
element that is synthesised and ejected (Tinsley 1980). If an el-
ement undergoes a net destruction during stellar nucleosynthesis
(e.g. hydrogen), then its yield will be negative, whereas the mass
of the element ejected will not.
c 0000 RAS, MNRAS 000, 000–000
5. Modelling element abundances 5
Figure 3. The mass of each element ejected from SNe-Ia, ac-
cording to the tabulation of Thielemann et al. (2003). Coloured
circles represent elements that are considered in this work.
forty two different element species. Unlike the AGB and SN-
II yields, the SN-Ia yields used here are independent of the
initial mass and metallicity of the progenitor system. The
total mass ejected in a SN-Ia is assumed to be 1.23M⊙, the
sum of the ejecta from the eleven elements considered in this
work. As no H or He is ejected by SNe-Ia, this sum equals
the mass of metals ejected. Fig. 3 shows the ejected mass
of each element. Iron is the most abundant, while there are
also non-negligible amounts of oxygen, silicon and nickel.
SN-Ia yields that depend on the initial mass and metal-
licity of the progenitors are now also available in the liter-
ature (e.g. Seitenzahl et al. 2013). We defer a study of the
effect of such yields on our GCE model to future work.
Rather than make assumptions about the type and life-
times of the progenitor systems involved, we instead use
observationally-motivated DTDs to define the lifetimes of
SN-Ia progenitors (see §4.1).
3.5 SN-II yields
Our preferred set of SN-II yields is tabulated by P98, and
also kindly provided by R. Wiersma (priv. comm.). This set
contains yields for initial masses ranging from 6 to 1000 M⊙,
and five initial metallicities from 0.0004 to 0.05. We only
consider the existence of stars up to 120 M⊙ here. Even
then, the range provided by the P98 yields is significantly
wider than, for example, the more commonly used yields of
Woosley & Weaver (1995), which only go up to 40M⊙.5
The
P98 set also takes account of mass loss through winds prior
to the SN. The inclusion of prior mass loss also effects the
composition of the explosive yields, as we explain below.
Fig. 4 shows the ejected mass of metals (top left panel),
5 Unlike the tables of Woosley & Weaver (1995), both sets of SN-
II yield tables considered in this work account for the decay of
nickel into iron shortly after the SN. P98 do so by simply adding
the 56Ni yield to that of 56Fe, and Chieffi & Limongi (2004) by
only tabulating yields 108s after the explosion.
total baryons (top right panel), and individual elements
(bottom two panels) from SNe-II as a function of initial
mass, as is done for AGB winds in Fig. 2. The dashed lines
in Fig. 4 indicate corrections to the C, Mg and Fe yields that
we include in our model, following the recommendation of
Wiersma et al. (2009, see their §A3.2). These ad hoc correc-
tions can be justified by uncertainties in the explosive yields
tabulated by Woosley & Weaver (1995), on which the P98
SN-II yields are based. These corrections halve the yield of C
and Fe and double the yield of Mg, relative to the originally
tabulated values.
We note that the P98 yields show some sudden drops
in the ejecta of certain elements. At low metallicities, the
reduction in yield of the heaviest elements above ∼ 30M⊙ is
due to them being locked in the stellar remnant. Remnant
masses increase significantly above ∼ 30M⊙ at low metal-
licities due to low mass-loss efficiency prior to the SN. This
effect is less severe for lighter elements, such as oxygen, as
‘pair creation’ SNe are believed to dominate over ‘core col-
lapse’ SNe above ∼ 60M⊙, allowing more of these elements
to be ejected. At higher metallicities, more efficient mass loss
prior to the SN inhibits large remnant formation. Increased
mass loss at Z0 0.02 from massive, Wolf-Rayet stars also
causes the larger He and C yields in this metallicity range.
The removal of these elements in the wind in turn suppresses
the explosive α element yields. For more details, see §5 of
P98.
These specific features could have a signficant impact
on our results. We therefore also test our GCE implementa-
tion with an alternative set of SN-II yields, that do not take
account of prior mass loss, and therefore appear more sta-
ble as a function of initial mass and metallicity. This second
set is taken from Chieffi & Limongi (2004, hereafter CL04).
These account for stars of initial masses from 13 to 35 M⊙,
and so require both an extrapolation downwards to the up-
per mass limit for AGB winds (chosen here to be 7M⊙), and
upwards to a more reasonable maximum mass. We choose
Mmax = 120M⊙ when using the CL04 SN-II yields in order
to match the maximum mass considered for the P98 SN-II
yields, and because such massive stars are known to exist
and contribute to chemical enrichment in the real Universe.
However, we caution that this represents a gross extrap-
olation into a regime well above that constrained by the
original yield calculations. For this reason we use the CL04
yields only as a comparison to those of P98, in order to dis-
cern what effect prior mass loss might have on our overall
results.
4 THE GCE EQUATION
In this section, we present the GCE equations required to
calculate the mass ejection rate from stars. The implemen-
tation of these equations into our semi-analytic model is
described in §5.
Following the prescriptions given by Tinsley (1980), the
total rate of mass ejected by an SSP at time t is given by
eM(t) =
MU
ML
(M − Mr) ψ(t − τM) φ(M) dM , (3)
where M is the initial mass of a star, τM is its lifetime, ψ(t−
c 0000 RAS, MNRAS 000, 000–000
6. 6 Yates et al.
Figure 4. Mass released by SNe-II from the Portinari, Chiosi & Bressan (1998) yield tables. Points indicate values from the yield tables.
Solid lines indicate the interpolation used between these points. Top left: The mass of metals ejected as a function of mass, for five
different initial metallicities. Top right: The total baryonic mass ejected as a function of mass, for five different initial metallicities.
Bottom left: The mass of each element ejected as a function of mass, for stars of Z0 = 0.004. Dashed lines indicate the corrected C, Mg
and Fe yields (see text). Bottom right: Same as bottom left, for stars of Z0 = 0.02.
τM) is the star formation rate when the star was born, Mr is
the mass of the stellar remnant, and φ(M) is the normalised
IMF by number, as given by Eqn. 1.
ψ(t−τM)·φ(M) gives us the birthrate of stars of mass M
at time t − τM. Multiplying this birthrate by (M − Mr), the
mass ejected by one star of mass M, then gives us the total
mass ejection rate by stars of mass M, at time t. We can
then integrate this quantity over a suitable range of masses
(ML to MU ) to obtain eM(t).
The same equation can be written when only consider-
ing the metals ejected by an SSP:
eZ(t) =
MU
ML
MZ(M, Z0) ψ(t − τM) φ(M) dM , (4)
where MZ = yZ(M, Z0)+Z0 ·(M −Mr) is the mass in metals
returned to the gas phase by a star of mass M (as clarified
by Maeder 1992, §4.1). This is made up of the mass- and
metallicity-dependent yield6
yZ, plus those metals present at
the formation of the star that are later ejected unprocessed,
Z0 · (M − Mr).
The same equation can be written again, when only
considering individual chemical elements ejected by an SSP,
6 We define the metal yield as a mass yZ, rather than the mass
fraction pZ proposed by Tinsley (1980), where yZ = MpZ.
replacing MZ with Mi = yi(M, Z0) + (Mi/M)(M − Mr),
the total mass of element i returned to the gas phase by a
star of mass M. However, for simplicity, we will proceed by
describing the GCE equation in terms of the total metals
ejected.
Eqn. 4 can be further split-up into four sub-components,
representing the three modes of ejection, AGB winds, SNe-Ia
and SNe-II:
eZ(t) =
7M⊙
0.85M⊙
MAGB
Z (M, Z0) ψ(t − τM) φ(M) dM
+ A
′
k
τ0.85M⊙
τ8M⊙
MIa
Z ψ(t − τ) DTD(τ) dτ
+ (1 − A)
16M⊙
7M⊙
MII
Z (M, Z0) ψ(t − τM) φ(M) dM
+
Mmax
16M⊙
MII
Z (M, Z0) ψ(t − τM) φ(M) dM . (5)
The first term in Eqn. 5 represents the contribution to the
ejected metals from AGB winds (approximating that the
material is shed at the end of the stars’ lives), with the sym-
bols representing the same quantities as in Eqn. 4. As can
be seen, the integral extends to masses above the minimum
mass of SN-Ia-producing binary systems (∼ 3M⊙). There-
c 0000 RAS, MNRAS 000, 000–000
7. Modelling element abundances 7
fore, we are explicitly accounting for the ejection of metals
during the AGB phase of such stars, prior to the SN.
The second term represents the contribution from SNe-
Ia, parameterised with an analytic DTD motivated by ob-
served SN-Ia rates (see §4.1). Using a DTD means we do not
have to make additional assumptions about the progenitor
type of SNe-Ia, the binary mass function φ(Mb), secondary
mass fraction distribution f(M2/Mb), or binary lifetimes in
our modelling. These uncertain parameters become prob-
lematic when using the theoretical SN-Ia rate formalism of
Greggio & Renzini (1983). The three SN-Ia DTDs that we
consider in this work are described in §4.1.
The coefficient A
′
in the second term of Eqn. 5 gives
the fraction of objects from the whole IMF that are SN-
Ia progenitors. This is subtly different from A in the third
term, which is the fraction of objects only in the mass
range 3-16M⊙ that are SN-Ia progenitors.7
As clarified by
Arrigoni et al. (2010a, §3.3), these two coefficients are re-
lated by A
′
= A · f3−16, where f3−16 is the fraction of all
objects in the IMF that have mass between 3 and 16M⊙.
Our chosen value of A is 0.028 (i.e. 2.8 per cent of the stellar
systems in the mass range 3 - 16M⊙ are SN-Ia progenitors),
as discussed in §5.4. The coefficient k is given by
k =
Mmax
Mmin
φ(M) dM , (6)
and gives the number of stars in a 1M⊙ SSP. For the
Chabrier IMF used here, f3−16 = 0.0385 and k = 1.4772
when assuming Mmin = 0.1M⊙ and Mmax = 120M⊙.
The third term in Eqn. 5 represents the ejection of met-
als, via SNe-II explosions, of all objects within the mass
range 7.0 M/M⊙ 16.0 that do not produce SNe-Ia.
Hence, the coefficient is (1 − A).8
The fourth term represents the contribution to the ejec-
tion of metals from single, massive stars exploding as SNe-II.
We note here that Eqn. 5 can also be rewritten so that
all the modes of enrichment are expressed as time integrals,
because the stellar lifetimes are a monotonic function of ini-
tial mass (e.g. P98, §8.7).
4.1 SN-Ia delay-time distribution
There have been many SN-Ia DTDs formulated in the liter-
ature. In this work, we consider three, shown in Fig. 5, and
compare the results obtained from each.
The first is the power-law DTD with slope −1.12 pro-
posed by Maoz, Mannucci & Brandt (2012), formed from a
fit to the SN-Ia rate derived from 66,000 galaxies (compris-
ing 132 detected SNe-Ia) from the Sloan Digital Sky Survey
II (SDSS-II):
DTDPL = a(τ/Gyr)−1.12
, (7)
7 The use of the mass range 3 - 16M⊙ relates to the assumed mass
range of SN-Ia-producing binary systems in the single-degenerate
scenario.
8 Note that, because the distribution of SN-Ia-producing binaries
is assumed to follow the distribution of all objects, the value of
A is the same for any mass range within 3 < M/M⊙ < 16.
Figure 5. The three SN-Ia delay-time distributions considered
in this work. The dashed line corresponds to the power-law DTD
given by Eqn. 7. The dotted line corresponds to the narrow Gaus-
sian DTD given by Eqn. 8. The solid line corresponds to the bi-
modal DTD given by Eqn. 9. All three DTDs are normalised over
the time range τ8M⊙
= 35 Myrs to τ0.85M⊙
= 21 Gyrs.
where τ is the delay time since the birth of the SN-
Ia-producing binary systems, and a is the normalisa-
tion constant, taken here to be a = 0.15242 Gyr−1
(see Eqn. 10). Similar power-law slopes have been sug-
gested by a number of other works (e.g. Totani et al. 2008;
Maoz Sharon & Gal-Yam 2010; Maoz & Mannucci 2012).
The second is the narrow, Gaussian DTD proposed by
Strolger et al. (2004), based on observations of 56 SNe-Ia in
the range 0.2 < z < 1.8 from the GOODS North and South
fields. This form is given by
DTDNG =
1
√
2πσ2
τ
e−(τ−τc)2
/2σ2
τ , (8)
where τ is again the delay time, τc = 1 Gyr is the character-
istic time (on which the Gaussian distribution is centered),
and στ = 0.2τc Gyrs is the characteristic width of the dis-
tribution.
The third is the bi-modal DTD proposed by
Mannucci, Della Valle & Panagia (2006), motivated by si-
multaneously fitting both the observed SN-Ia rate and the
distribution of SNe-Ia with galaxy B-K colour and radio
flux, for a collection of samples over the redshift range
0.0 < z < 1.6. This DTD includes a ‘prompt’ component
of SNe-Ia (∼ 54 per cent of the total) that explode within
∼ 85 Myr of the birth of the binary, followed by a broader,
delayed distribution. The Mannucci, Della Valle & Panagia
(2006) DTD has been expressed by Matteucci et al. (2006)
as
log(DTDBM) =
1.4 − 50(log(τ/yr) − 7.7)2
if τ < τ0
−0.8 − 0.9(log(τ/yr) − 8.7)2
if τ > τ0
,
(9)
where τ is the delay time, and τ0 = 0.0851 Gyr is the char-
acteristic lifetime separating the two components.
c 0000 RAS, MNRAS 000, 000–000
8. 8 Yates et al.
For all of these DTDs, the normalisation requirement
is,
τmax
τmin
DTD(τ) dτ = 1 , (10)
where τmin = τ8M⊙ and τmax = τ0.85M⊙ are the mini-
mum and maximum assumed lifetimes of a SN-Ia-producing
binary in the single-degenerate scenario (i.e. the lifetimes
of the largest and smallest possible secondary stars), re-
spectively. Strictly, their values depend on the stellar
lifetime tables used, and therefore also on the metallic-
ity of the stars. However, we choose to fix their values
for Eqn. 10 to those provided by the P98 lifetime ta-
bles for stars of Z0 = 0.02, namely τmin = 35 Myrs
and τmax = 21 Gyrs. Our chosen value of τmin = 35
Myrs is in line with those commonly used in the litera-
ture, with assumed values ranging from ∼ 30 Myrs (e.g.
Matteucci & Greggio 1986; Padovani & Matteucci 1993;
Matteucci & Recchi 2001; Matteucci et al. 2009) to ∼ 40
Myrs (e.g. Greggio 2005). This choice also means that ∼ 48
per cent of SNe-Ia explode within 400 Myrs when using the
power-law DTD, which is close to the ∼ 50 per cent pre-
dicted from observations of the SN-Ia rate by Brandt et al.
(2010), and around the lower limit determined from SN
remnants in the Small and Large Magellanic Clouds by
Maoz & Badenes (2010).
5 IMPLEMENTATION
The GCE equation given by Eqn. 5 has been implemented
into our semi-analytic model so that the mass of chemical
elements ejected is calculated at each simulation timestep.
The key aspects of this implementation are outlined in the
following sub-sections.
5.1 SFH, ZH and EH arrays
There are three galaxy-dependent values that are required
for us to predict ejection rates from stars: the star forma-
tion history (SFH), the total gas-phase metallicity history
(ZH) and the gas-phase element abundance history (EH).
The SFH is required to identify ψ(t − τM), the ZH is re-
quired to identify Z0, and the EH is required to calculate
the unprocessed ejecta of each individual element within the
semi-analytic model.9
We accommodate these histories into
arrays in our code.
The L-Galaxies time structure is made up of 63 snap-
shots (when run on the Millennium simulation), each con-
taining 20 timesteps. As there are nearly 26 million galaxies
by z = 0 in the semi-analytic model, it would require a sig-
nificant amount of memory for us to store the full histories
of each galaxy at the resolution of one timestep. Therefore,
we instead take a more dynamic approach; each galaxy has
9 Although the total gas-phase metallicity history could be de-
rived by simply summing the element abundances, keeping two
separate history arrays gives us the freedom to vary the number
of chemical elements we choose to track, and also to easily record
the relative contribution of the three ejection modes to the total
metal production.
Figure 6. The evolution of the first five bins (rows) of a his-
tory array for an isolated galaxy. The numbers represent the time
width of a bin in units of one timestep. At every timestep in the
code (columns, moving left to right), a new bin is ‘activated’.
Active bins are coloured in the schematic (grey for single-width
bins, red for double-width bins, and green for quadruple-width
bins). When three or more active bins have the same width, two
of the bins are immediately merged, as indicated at the top of the
schematic.
SFH, ZH and EH arrays of only 20 array-elements (here-
after, time ‘bins’). As time elapses in the simulation, the
width of older bins (those storing data from higher red-
shifts) increases, while new bins are ‘activated’ with a de-
fault width of one timestep. Thus, the whole history of each
galaxy can be stored with a time resolution that decreases
with lookback time. High precision at recent times is espe-
cially important when calculating galaxy luminosities as a
post-processing step, as young stars from recent star forma-
tion episodes tend to dominate the light. The evolution of
these history arrays with time is illustrated in the schematic
in Fig. 6. We have checked that changing the number of bins
in the history arrays does not affect the chemical evolution
in the model by testing our model with a range of history
bin resolutions including full resolution (i.e. 63×20 bins per
galaxy).
By z = 0, the older bins in such histories can be up
to ∼ 3 Gyrs wide. This is acceptable when calculating the
chemical enrichment within the code, as the bins are inte-
grated over more finely at each timestep (see §5.2). However,
when plotting relations using only the output z = 0 history
bins, the lower resolution at high-z does not correctly repre-
sent the smooth chemical evolution actually occuring in our
model. In these cases (for example, the [Fe/H]-[O/Fe] rela-
tion in Fig. 11), we construct higher resolution histories as
a post-processing step, by ‘stitching together’ the highest-
resolution bins from the histories of all output snapshots,
rather than just those from z = 0. This procedure is il-
lustrated by the schematic in Fig. 7. In this way, a much
smoother evolution can be plotted, which more accurately
represents the chemical evolution occuring within the code.
We note that when doing this for the disc components of
galaxies, account needs to be taken of stars that move from
the disc to the bulge through disc instabilities, by ensuring
that the total mass formed in the stitched-together bins does
c 0000 RAS, MNRAS 000, 000–000
9. Modelling element abundances 9
Figure 7. Schematic illustrating how history arrays are ‘stitched
together’ in post processing to form higher-resolution histories
when plotting data. At every output snapshot (y axis), a galaxy
has a series of history bins (black boxes). The most recent bins
from each output (in green) are extracted and used to form a
higher-resolution, non-overlapping history (shown in the bottom
row). The other bins (in red) are discarded. So that there are no
gaps in the reconstructed histories, a fraction of the mass from
partially overlapping bins is also included (in orange). This means
that many hundreds of bins (depending on the formation time of
the galaxy) can be used to make plots, rather than only 20 from
the z = 0 history. The inlay shows a zoom-in of the bottom-right
region of the main schematic.
not exceed the mass formed in the z = 0 history bins over
the same time span.
5.2 Implementing the GCE equation
In order to model GCE, Eqn. 4 needs to be implemented
into L-Galaxies as an algorithm, involving numerical in-
tegration and interpolation between values in a number of
look-up tables. All non-model-dependent terms (i.e. every-
thing except the SFHs, ZHs and EHs) are pre-calculated and
stored in look-up tables, in order to speed-up the runtime of
the code. This is possible because the time structure of the
history arrays is, by construction, the same for all galaxies
at any given time. Therefore, we can know a priori the range
of masses of stars that will explode in any given timestep.
We can re-write Eqn. 4 as
eZ(t) = ψ(t − τ)
MU
ML
MZ(M, Z0) · φ(M) dM , (11)
where ψ(t − τ) can be put outside the integral if we assume,
for each thin strip of the SFH integrated, that all the stars of
mass ML M MU are born at the same time (i.e. τML =
τMU = τ). We can then pre-calculate the integral in Eqn.
11 numerically to obtain a value for each initial metallicity,
in every history bin of every timestep that the semi-analytic
model will run through, and store it in a 3-dimensional look-
up table. The true value of Z0 for a given galaxy is then
used within the semi-analytic model to interpolate between
these pre-calculated results at each timestep, and ψ(t−τ) is
multiplied-in. The total mass in metals ejected is then given
by eZ(t) · ∆t, where ∆t is the width of the timestep. The
same procedure is used to obtain the total mass ejected,
and the total amount of each chemical element ejected at
each timestep. Once the ejected masses are calculated, we
transfer the material to either the galaxy’s ISM or CGM, as
described in §5.3.3.
5.3 Infall, Cooling and Outflows
The chemical enrichment recipe outlined above is only part
of the relevant physics needed to accurately model the chem-
ical evolution of galaxies. The distribution of these metals
between the various components of galaxies, and out into the
IGM, as well as the infall and cooling of gas, are also impor-
tant considerations when looking beyond a simple closed-box
model. Treatments of these physical processes are already
incorporated into L-Galaxies, as described by Guo et al.
(2011). A brief outline is also given below.
We note here that L-Galaxies considers three classes
of galaxy: those at the centre of a main DM halo, also known
as a ‘friends-of-friends (FOF) group’ (type 0 galaxies), those
at the centre of their own DM subhalo but not of their asso-
ciated FOF group (type 1 galaxies), and those galaxies that
have lost their DM subhalo through tidal disruption but
have not yet merged with a central galaxy or been tidally
disrupted themselves (type 2 galaxies). The prescriptions for
the physical processes included in the model are then ap-
plied to galaxies according to their type. For example, infall
of pristine gas is only allowed to occur for type 0 galax-
ies, whereas stripping of hot gas can only occur for type 1
galaxies (once they are within the virial radius of the central
galaxy).
5.3.1 Infall
The mass of pristine gas (assumed to be 75 per cent hydro-
gen and 25 per cent helium) infalling onto the DM halo is
simply determined by the difference between the assumed
baryon fraction fb and the actual baryon fraction Mb/MDM
in the DM halo. The assumed baryon fraction is reduced
from the cosmic baryon fraction fb,cos (assumed to be 0.17,
as given by WMAP1) due to reionisation, and is parame-
terised following Gnedin (2000) as
fb(z, Mvir) = fb,cos 1 + (22/3
− 1)
Mvir
Mc(z)
−2 −3/2
, (12)
where Mvir is the virial mass of the DM halo, and Mc(z) is
the chosen charateristic halo mass, whose dependence on
redshift has been calculated by Okamoto, Gao & Theuns
(2008). In this formalism, fb tends towards fb,cos as Mvir
c 0000 RAS, MNRAS 000, 000–000
10. 10 Yates et al.
increases. Pre-enriched gas can also be re-accreted onto the
DM haloes of central galaxies, in addition to this pristine
infall (see §5.3.3).
5.3.2 Cooling
Following White & Frenk (1991), the cooling of gas from the
CGM onto the disc is considered to fall into two regimes; at
early times and in low-mass DM haloes, gas is able to cool
rapidly in less than the free-fall time, with the cold-flow
accretion onto the central galaxy modelled as
˙Mcool =
Macc
tdyn,h
, (13)
where Macc is the mass of gas accreted onto the DM
halo, and the dynamical time of the DM halo is tdyn,h =
Rvir/Vvir = 0.1H(z)−1
. At late times and in massive DM
haloes, the accretion shock radius is large, leading to the
formation of a hot gas atmosphere. In this case, the accre-
tion rate onto the central galaxy is reduced to
˙Mcool =
rcool
Rvir
Mhot
tdyn,h
. (14)
Here, the cooling radius rcool is set by the cooling func-
tion of Sutherland & Dopita (1993), and Mhot is the mass
of shocked gas in the hot gas reservoir (see Guo et al. 2011,
§3.2). This accreted gas is then able to form stars, following a
simplified form of the Kennicutt-Schmidt law (see Guo et al.
2011, §3.4).
5.3.3 SN feedback
SNe explosions can reheat cold gas and also eject it from the
DM halo of galaxies. In previous versions of L-Galaxies,
the amount of energy released by SNe was assumed to be
proportional to the mass of stars formed ∆M∗ at that time.
Now that we have discarded the instantaneous recycling ap-
proximation, it is more appropriate to relate this energy to
the mass of material released by stars at that time. The to-
tal amount of energy produced by SN feedback is therefore
parameterised as
ESN = ǫh ·
1
2
eM(t)∆tV 2
SN , (15)
where ǫh is the halo-velocity-dependent SN energy efficiency,
eM(t) · ∆t is the mass released by stars in one timestep (see
Eqn. 3), and VSN is the SN ejecta speed, assumed to be
fixed at 630 km/s. This differs from the prescription used
by Guo et al. (2011) in the use of eM(t) · ∆t rather than
∆M∗. Due to this change, we have doubled the value of ǫh,
in order to have the same total SN feedback energy (ESN) as
previously used in the model. A thorough investigation into
the precise values of model parameters required following
our new GCE implementation is reserved for future work.
In our new, default GCE implementation, all stars dying
in the stellar disc release material and energy into the ISM,
whereas stars dying in the bulge and stellar halo release
material and energy into the hot CGM. The energy dumped
into the ISM by disc stars can then be used to reheat and
possibly eject some (fully mixed) cold gas. Energy dumped
into the CGM can also contribute to ejection. The amount
of gas ejected from the DM halo into an external reservoir
is given by
∆Mejec =
ESN − 1
2
ǫdisceM(t)∆tV 2
vir
1
2
V 2
vir
, (16)
where ǫdisc · eM(t) · ∆t is the amount of gas that is reheated
but does not escape the potential well. The ejected gas is
then allowed to return to the DM halo over timescales that
are proportional to Vvir/tdyn,h.10
This constitutes a second
component of gas infall that has been pre-enriched by the
galaxy.
We have also implemented an alternative feedback pre-
scription which includes metal-rich winds. These winds
dump some material released by disc SNe-II directly into
the hot gas. This scheme is discussed in §6.3.3.
5.4 Default set-ups
There can be many free parameters involved when develop-
ing a chemical enrichment model. We have limited ourselves
to only one new free parameter: the fraction, A, of objects in
an SSP in the range 3 M/M⊙ 16 that are SN-Ia progen-
itors.11
A is specifically ‘tuned’ so that the peak of the [Fe/H]
distribution for G dwarfs in our MW-type galaxy sample is
around the solar value (see §6.2). An increase in A corre-
sponds to an increase in [Fe/H], and we find that the best
value is A ∼ 0.028 for all three of the DTDs we consider (see
§4.1). A single value of A was also found to be suitable for
a range of different SN-Ia DTDs by Matteucci et al. (2009).
All other results discussed in this work are obtained with-
out further tuning. In the following, we label results using
the bi-modal, power-law, and narrow Gaussian DTDs with
‘BM’, ‘PL’ and ‘NG’, respectively.
We note that our preferred value of A = 0.028 is
similar to that commonly found in the literature. For ex-
ample, Greggio (2005) took a value of A
′
= 0.001 when
also using a Chabrier IMF, which equates to a value of
A = 0.026. Similarly, de Plaa et al. (2007) take a pre-
ferred value of 0.027 for a Kroupa IMF (assuming a SN-
Ia progenitor mass range of 1.5 − 10M⊙). Arrigoni et al.
(2010a) allow for a value between 0.015 and 0.05, preferring
0.03 when using a slightly top-heavy Chabrier IMF (i.e. a
slope of 2.15 rather than 2.3 for M > 1M⊙, see Eqn. 1).
Other works, which have used IMFs with a smaller frac-
tion of stars above 1M⊙, have taken slightly higher values.
For example, Matteucci & Recchi (2001) and Fran¸cois et al.
(2004) prefer A = 0.05 when using a Scalo (1986) IMF.
10 Henriques et al. (2013) have found that scaling the reincorpo-
ration time to the inverse of the DM halo mass allows the semi-
analytic model to better reproduce the evolution of the galaxy
stellar mass and luminosity functions with redshift. We will in-
corporate this improvement with our new GCE model in future
work.
11 We note again that the SN efficiency parameter ǫh has also
been modified to ensure that the total SN feedback energy is
unchanged (see §5.3.3). All other model parameters have been
kept to the values used by Guo et al. (2011).
c 0000 RAS, MNRAS 000, 000–000
11. Modelling element abundances 11
Figure 8. The M∗-Zcold relation (where Zcold = 12 +
log(NO/NH)) for L-Galaxies with the new GCE implementa-
tion and using a power-law SN-Ia DTD (points and black lines).
This relation is compared to that of L-Galaxies prior to the new
GCE implementation (red lines), and a fit to the observed M∗-
Zg relation for emission-line galaxies from the SDSS-DR7 (orange
lines) by Yates, Kauffmann & Guo (2012).
Calura & Menci (2009) and Matteucci et al. (2006) take val-
ues of A
′
= 0.0020 and 0.0025 for a Scalo IMF, which cor-
responds to A ∼ 0.05 and 0.06, respectively. And P98 find
A = 0.05 - 0.08 when using a Salpeter IMF (and a SN-Ia
progenitor mass range of 3 − 12M⊙).
Our chosen value of A ∼ 0.028 is also in line with expec-
tations from observations of the SN-Ia rate, with the fraction
of SN-Ia-producing stars in the range 3 - 8M⊙ believed to
be between 0.03 and 0.1 (Maoz & Mannucci 2012). For the
range 3 - 16M⊙, this equates to between ∼ 0.024 and 0.081
(for a Chabrier IMF).
6 RESULTS
In the following sub-sections, we compare results from our
updated semi-analytic model to observational data for local
star-forming galaxies (§6.1), Milky Way disc stars (§6.2) and
local elliptical galaxies (§6.3). In doing so, we are attempt-
ing both to assess the success of our GCE implementation
and to further constrain which of the SN-II yield tables and
SN-Ia DTDs described in §3 and §4.1 perform best across
the range of data considered. In what follows, ‘element en-
hancement’ refers to the ratio of element x to iron, [x/Fe],
and ‘element abundance’ refers to the ratio of element x to
hydrogen, [x/H].12
Throughout this work, we normalise our
model values to the set of solar abundances used for the
12 The element ratios discussed in this work are normalised to
solar values, using the following equation: [x/y] = log(Mx/My)−
log(Mx⊙/My⊙). Note that Mx/My = (Ax/Ay) · (ǫx/ǫy), where
Ax is the atomic weight of element x, log(ǫx) = log(nx/nH) + 12
is the abundance of element x, and nx is the number density of
Figure 9. The M∗-Z∗ relation (where Z∗ = log(M∗,Z/M∗/0.02))
for L-Galaxies with the new GCE implementation and using a
power-law SN-Ia DTD (points and black lines). This relation is
compared to that of L-Galaxies prior to the new GCE imple-
mentation (red lines), the observed relation from the SDSS-DR2
(orange lines) by Gallazzi et al. (2005), a fit to the mass-weighted
relation from the SDSS-DR3 (green line) by Panter et al. (2008),
and to a set of Local Group dwarf galaxies (blue lines) by
Woo, Courteau & Dekel (2008).
observations to which we compare. For clarity, we have se-
lected a representative sample of ∼ 480000 z = 0 galaxies
and their progenitors for the plots in this section.
6.1 The mass-metallicity relations
One of the key diagnostics used to analyse the chemical evo-
lution of galaxies is the relation between their stellar mass
(M∗) and gas-phase metallicity (Zg). The large statistical
power of the SDSS allowed Tremonti et al. (2004) to deter-
mine the M∗-Zg relation for emission-line galaxies in the
local Universe. They found a clear positive correlation be-
low ∼ 1010.5
M⊙ with a 1σ scatter of only 0.1 dex. Above
this mass, the relation was found to flatten. Here, we com-
pare our z = 0 model mass-metallicity relations for gas and
stars with those observed. We also have the opportunity to
directly compare L-Galaxies results before and after the
new GCE implementation – something we are not able to
do when discussing individual element ratios in later sub-
sections.
Fig. 8 shows the M∗-Zcold relation for L-Galaxies with
the new GCE implementation and using the power-law DTD
(points and black lines). 95600 model galaxies were selected
such that log(M∗) 8.6 and −2.0 log(SFR) 1.6, in
order to match the dynamic range of the SDSS-DR7 obser-
vations. We note here that both the gas-phase and stellar
mass-metallicity relations are very similar for all three of
the DTDs considered. This is because the SN-Ia DTD has
atoms of element x. For hydrogen, AH = 1.008 and log(ǫH) =
12.0.
c 0000 RAS, MNRAS 000, 000–000
12. 12 Yates et al.
little impact on the abundance of oxygen, which is the most
abundant heavy element and is produced predominantly by
SNe-II.
In Fig. 8 we also plot a fit to the same relation for
L-Galaxies prior to the new GCE implementation (red
lines), and a fit to the observed M∗-Zg relation from the
SDSS data release 7 (SDSS-DR7) (orange lines).13
We can
see that there is very good agreement between the obser-
vations and our new model at z = 0. Both the slope and
amplitude of the new model relation are in better agree-
ment with observations than those of the previous model.
The increase in amplitude at lower mass is due to a) our
new GCE implementation (i.e. the input yields) allowing
a different amount of metal into the ISM than the fixed 3
per cent yield assumed before, and b) our new SN feedback
scheme allowing more oxygen to stay in the ISM after it is
released by stars, rather than being instantly ‘reheated’ into
the CGM. This is because the energy input by a population
of SNe is now distributed over time, rather than all dumped
at once into the ISM straight after star formation, when a
lot of oxygen is also released (see §5.3.3).
The scatter of our new model M∗-Zg relation is
slightly larger than that seen in the SDSS. Study-
ing the properties of outliers above and below the
M∗-Zg relation can tell us a lot about the evolution
of galaxies (e.g. Dellenbusch, Gallagher & Knezek 2007;
Peeples, Pogge & Stanek 2008; Zahid et al. 2012a). We de-
fer a detailed analysis of such galaxies in our model to later
work.
We note here that the gas-phase metallicity is now
defined as Zcold = 12 + log(NO/NH) in our new model,
in exactly the same way as in observations, where NO
and NH are the number of atoms of oxygen and hydro-
gen, respectively. Previously, the approximation Zcold =
9.0 + log(MZ,cold/Mcold/0.02) was used, where 9.0 was the
assumed solar oxygen abundance and 0.02 the assumed so-
lar metallicity. The difference in the value obtained when
using these two methods is only small, with the new formu-
lation estimating a metallicity ∼ 0.04 dex lower than the old
formulation.
Fig. 9 shows the z = 0 relation between the stellar
mass and stellar metallicity (Z∗) of our model galaxies (us-
ing a power-law DTD), after our new GCE implementa-
tion (points and black lines), and prior to it (red lines). In
both cases, solar-normalised metallicities are calculated as
Z∗ = log(M∗,Z/M∗/0.02), using the same solar metallicity
of Z⊙ = 0.02 assumed in the stellar population synthesis
models that obtained stellar metallicities in the SDSS-DR2
(A. Gallazzi, priv. comm.).
Below M∗ = 1010.5
M⊙, the new model M∗-Z∗ relation
is similar in shape to that of the previous model, but with
an amplitude ∼ 0.1 dex higher. This is also higher than
observed at low mass (although this is a region where obser-
vations are are not well constrained). The mass-weighted
M∗-Z∗ relation of Panter et al. (2008) (green line) from
13 This fit to the SDSS-DR7 is given by 26.6864 −
6.63995 log(M∗) + 0.768653 log(M∗)2 − 6.0282147 log(M∗)3,
and is an updated version of the SDSS-DR2 relation
from Tremonti et al. (2004), using twice as many galaxies
(Yates, Kauffmann & Guo 2012).
Figure 10. Three example SFHs from our MW-type model sam-
ple. Filled circles represent the histories as recorded by the 20
SFH bins at z = 0. Open circles represent the SFRs at every
output snapshot of the simulation.
the SDSS-DR3 probably provides the best comparison with
our model, as we also consider mass-weighted metallici-
ties. The Panter et al. (2008) relation also shows good cor-
respondance with observations of Local Group dwarfs by
Woo, Courteau & Dekel (2008) (blue lines). We can see that
the general trend of decreasing Z∗ with M∗ is reproduced
in our model, despite low-M∗, star-forming model galaxies
being too metal-rich by z = 0.
Henriques & Thomas (2010) have shown that a more
realistic treatment of stellar disruption, whereby satellite
galaxies have their stellar component gradually stripped,
can help steepen the slope of the M∗-Z∗ relation in semi-
analytic models. This could bring the low-mass end of our
model relation into better agreement with observations. In-
cluding such a gradual disruption scheme into L-Galaxies
will be the focus of future work.
The model M∗-Zcold and M∗-Z∗ relations when using
the CL04 SN-II yields have slightly shallower slopes and are
∼ 0.1 dex higher than those assuming the P98 yields. They
therefore have a higher amplitude than observed. This is
because the CL04 yield set allows more oxygen to be pro-
duced and ejected from stars when extrapolated to 120M⊙,
particularly at low metallicity.
To conclude this section, we can say that our new GCE
implementation improves the correspondance between our
model and observations of gas-phase metallicities in local,
star-forming galaxies. This was by no means a foregone con-
clusion, considering the significant changes to the chemical
evolution modelling we have implemented. However, further
improvement to the semi-analytic model is still required in
order to better match the observed total stellar metallicities
of galaxies at z = 0.
6.2 The Milky Way disc
There is now a wealth of data available in the literature on
the chemical composition of stars in the MW disc. These
data allow us to put firm constraints on the success of
our GCE implementation in reproducing realistic MW-type
model galaxies. We construct a sample of ∼ 5200 central
(type 0) galaxies at z = 0 that are disc dominated (i.e.
Mbulge/(Mbulge + Mdisc) < 0.5), with DM halo masses in
c 0000 RAS, MNRAS 000, 000–000
13. Modelling element abundances 13
Figure 11. The [Fe/H]-[O/Fe] relation for G dwarfs in the stellar
discs of our MW-type model galaxy sample when using a bi-modal
(top panel), power-law (middle panel), and narrow Gaussian (bot-
tom panel) SN-Ia DTD. One galaxy contributes many hundreds of
points to this relation (see §5.1). The greyscale indicates the dis-
tribution of SSPs, weighted by the mass formed. Contours show
the 68th, 95th, 99th and 99.9th percentiles. The chemical evolu-
tion of an individual MW-type model galaxy is over-plotted on
each panel (red tracks), and discussed in detail in §6.2.2. Points
on the track denote the chemical composition at discreet times in
the past, labelled by the lookback time in Gyrs. The SFH of the
same galaxy is plotted in red in Fig. 10.
the range 11.5 log(Mvir)/M⊙ 12.5, and recent star for-
mation rates of 1.0 SFR/M⊙yr−1
10.0 over the redshift
range 0.0 z 0.25 (i.e. the last ∼ 3.0 Gyrs). Our results
are not affected by small changes to these criteria. Three
example star formation histories (SFHs) from our MW-type
model sample are shown in Fig. 10. The chemical evolution
of the individual galaxy depicted in red is discussed in §6.2.2.
In this section, the model values are normalised to the solar
abundances determined by Anders & Grevesse (1989).
In order to compare with observations, we only con-
sider G dwarfs (0.8 M/M⊙ 1.2) still present in the
stellar discs of our model MW-type galaxies at z = 0. When
using the P98 stellar lifetimes (§3.2), not all G dwarfs live as
long as the age of the MW disc. For example, stars of mass
1.2M⊙ (the upper mass limit we assume for G dwarfs) live
from 3.1 Gyrs at Zinit = 0.0004 to a maximum of 4.7 Gyrs at
Zinit = 0.02 (see Fig. 1). These timescales are clearly shorter
than the typical ages of the oldest SSPs in our MW-type
model discs14
(see Fig. 10). Therefore, we re-weight those
SSPs for which some of the G dwarfs would no longer be
present at z = 0 for the plots in this section. This correction
removes a very small contribution from the oldest SSPs, re-
ducing very slightly the number of low-[Fe/H], high-[O/Fe]
stars. Although this is a more rigorous treatment, the main
conclusions drawn from our MW-type sample also hold when
assuming that all G dwarfs survive up to z = 0.
6.2.1 MW-type model galaxies
Fig. 11 shows the [Fe/H]-[O/Fe] relation for the G dwarfs in
the stellar discs of our model MW-type galaxies, using the
stitched-together histories described in §5.1, for the three
DTDs we consider. Care needs to be taken when compar-
ing Fig. 11 to observations. In observational studies of the
MW disc, the chemical composition of individual stars of
various ages are measured and plotted. In the case of our
semi-analytic model, individual stars cannot be resolved,
and so we must instead rely on the chemical composition
of each population of stars, formed at each timestep during
the evolution of a galaxy. Fig. 11 therefore shows the chem-
ical composition of SSPs from ∼ 5200 MW-type galaxies,
where one MW-type galaxy contributes many hundreds of
points (see §5.1). Considering a whole sample of MW-type
galaxies provides a statistically significant indication of the
typical variation in the chemical composition of MW-type
discs in our model. This method of comparison has been used
before in semi-analytic models (e.g. Calura & Menci 2009).
Note that we therefore weight the SSPs by the mass of stars
formed. The evolution of an example, individual MW-type
galaxy is also plotted in each of the panels in Fig. 11 (red
tracks). This galaxy is discussed in detail in §6.2.2.
Each of the panels in Fig. 11 shows a clear decrease
in [O/Fe] with increasing [Fe/H] towards the solar com-
position. There are, however, important differences in the
distribution of SSPs for each of the three DTDs we con-
sider. These differences can be seen more clearly in Fig.
12, where we compare the [Fe/H] and [O/Fe] distributions
when using our three DTDs (black histograms) with those
14 The smallest G dwarfs considered (0.8M⊙) can live from
around 14 to 26 Gyrs, and so do survive the age of the disc.
c 0000 RAS, MNRAS 000, 000–000
14. 14 Yates et al.
Figure 12. Top row: [Fe/H] distributions for the stellar discs of our model MW-type galaxies, when using a bi-modal (left), power-
law (middle), or narrow Gaussian (right) SN-Ia DTD. Vertical dashed lines indicate the solar iron abundance. Bottom row: [O/Fe]
distributions for the same model discs and DTDs. Vertical dashed lines indicate the solar oxygen abundance.
Figure 13. Top row: [Fe/H] distributions for the stellar discs of our model MW-type galaxies, when using a bi-modal (left), power-
law (middle), or narrow Gaussian (right) SN-Ia DTD. Vertical dashed lines indicate the solar iron abundance. Bottom row: [O/Fe]
distributions for the same model discs and DTDs. Vertical dashed lines indicate the solar oxygen abundance.
of 16,134 F and G dwarfs from the Geneva-Copenhagen
Survey (GCS, orange histograms) (Nordstr¨om et al. 2004;
Holmberg, Nordstr¨om & Andersen 2009) and 293 unique
G dwarfs from the Sloan Extension for Galactic Under-
standing and Exploration (SEGUE, red histograms) survey
(Yanny et al. 2009; Bovy et al. 2012a,b).
The difference in [Fe/H] distribution between the two
observational samples is likely due to their different depths;
the GCS probed strictly the solar neighbourhood (7.7
RGC/kpc 8.31 and 0.0 |ZGC|/kpc 0.359), whereas
SEGUE covered a wider range of galactic radii but also
much higher galactic scale heights (5 RGC/kpc 12 and
0.3 |ZGC|/kpc 3.0).15
This means that the SEGUE
sample includes a larger number of metal-poor, ‘thick-disc’
stars, and so has a [Fe/H] distribution spread to lower iron
abundances. Our model, in turn, represents the average
15 In Fig. 12 the stars with |ZGC| < 0.3 that are missing from
the SEGUE survey are accounted for via the mass re-weighting
of the [Fe/H] distribution described by Bovy et al. (2012a).
chemical composition of stars born at each timestep in the
discs of MW-type galaxies, due to the full mixing of material
in the various galactic components.
The model [Fe/H] distributions for all three of our set-
ups are in reasonable agreement with the GCS data (partly
by construction, as we have tuned A to obtain a peak of the
[Fe/H] distribution around 0.0), although the NG set-up is
skewed slightly more to higher iron abundances. However,
there are significant differences in the model [O/Fe] distri-
butions. For example, the high-[O/Fe] tail in our BM set-up
is much less extended than seen in the [α/Fe] distribution
from the SEGUE survey16
. This suggests that stars are be-
ing enriched with iron too quickly when using the bi-modal
DTD – a conclusion also reached by Matteucci et al. (2009).
16 Note that Bovy et al. (2012a) and Bovy et al. (2012b) choose
[α/Fe] to be the average of [Mg/Fe], [Si/Fe], [Ca/Fe] and [Ti/Fe],
with no oxygen lines included in the analysis. However, as oxygen
is the most abundant α element in galaxies, a comparison between
their [α/Fe] and our [O/Fe] is still valid here.
c 0000 RAS, MNRAS 000, 000–000
15. Modelling element abundances 15
Figure 14. The evolution, from redshift 7 to 0, of the mass (in M⊙), SFR (in M⊙/yr), iron abundance, total metallicity, and heavy
element enhancements of four different galaxy components (see legend) in the example MW-type model galaxy shown in Fig. 11, using
the power-law DTD.
Interestingly, the extent of the high-[O/Fe] tail in the
[O/Fe] distribution increases from left to right in Fig. 12.
This is due to the different number of ‘prompt’ SNe-Ia as-
sumed for each of the three DTDs. The smaller the prompt
component, the larger the number of low-[Fe/H], high-
[O/Fe] stars that can be formed before a significant amount
of Fe gets into the star-forming gas. The bi-modal DTD al-
lows ∼ 54 per cent of SNe-Ia to explode within 100 Myrs of
star formation (∼ 58 per cent within 400 Myrs), the power-
law DTD allows ∼ 23 per cent within 100 Myrs of star for-
mation (∼ 48 per cent within 400 Myrs), and the Gaussian
has no prompt component at all. Only the Gaussian DTD
has a high-[O/Fe] tail as extended as that seen for G dwarfs
from SEGUE. However, we reiterate that the lack of any
prompt component is in contradiction with recent observa-
tions (e.g. Maoz & Mannucci 2012). The smaller high-[O/Fe]
tail produced when using the power-law DTD, although not
as extended as seen in the SEGUE data, is still promising,
espcially when considering that a) the SEGUE data contain
a large number of α-enhanced, iron-poor stars at high galac-
tic scale heights, and b) our model represents the chemical
composition of MW-type stellar discs in a statistical sense,
and also assumes full mixing of metals in the stellar disc.17
We will also show in §6.3 that the power-law DTD also pro-
duces positive slopes in the M∗-[α/Fe] relations of elliptical
galaxies.
In Fig. 13 we show a finer binning of the model [Fe/H]
17 Including a treatment of the radial distribution of metals in
galaxies, similar to that done by Fu et al. (2013), will be the focus
of future work.
and [O/Fe] distributions for the three SN-Ia DTDs consid-
ered (black histograms). Sub-distributions for three distinct
age ranges (coloured histograms) are also plotted. All panels
show nicely that older SSPs have lower [Fe/H] and higher
[O/Fe] than younger SSPs, due to the delayed enrichment of
the star-forming gas with iron from SNe-Ia. There is also no
sign of an extended tail below [Fe/H] = −1.0 (the ‘G-dwarf
problem’) that is common to closed-box models.
The broader plateau present in the [O/Fe] distribution
for the PL set-up is due to the shape of the DTD; the power-
law DTD assumes a smoother change in SN-Ia rate with
time than the other two DTDs considered (see Fig. 5). This
means that the ISM in a typical MW-type galaxy undergoes
a fairly constant decrease in [O/Fe] of ∼ 0.025 dex/Gyr for
the power-law DTD. In contrast, the bi-modal DTD causes
a more gradual decrease in [O/Fe] of ∼ 0.016 dex/Gyr, after
significantly enriching the ISM with iron shortly after the
start of star formation. In turn, the Gaussian DTD produces
a steep decrease in [O/Fe] of ∼ 0.066 dex/Gyr from very high
initial values until ∼ 1 Gyr after the peak of star formation,
with little change thereafter.
The CL04 SN-II yields produce qualitatively similar re-
sults to those discussed above, except that the [Fe/H] dis-
tribution is shifted to higher values and the [O/Fe] has a
decreased high-[O/Fe] tail – in greater contradiction with
observations. This is because, when extrapolated to 120M⊙,
the CL04 yields predict a higher production of O, Mg and
Fe by SNe-II than the P98 yields, particularly at low metal-
licity.
c 0000 RAS, MNRAS 000, 000–000
16. 16 Yates et al.
6.2.2 An individual MW-type model galaxy
In this sub-section, we look more closely at the chemical evo-
lution of an individual MW-type galaxy in our model. This
galaxy’s SFH is plotted in red in Fig. 10, and its evolution in
the [Fe/H]-[O/Fe] diagram is shown by a red track in each
panel of Fig. 11. Points on the tracks in Fig. 11 denote the
chemical composition at discreet times in the past, labelled
by the lookback time in Gyrs.
This galaxy nicely demonstrates the fairly smooth evo-
lution that we would expect from a MW-type galaxy. How-
ever, it is not necessarily typical of our MW-type model sam-
ple as a whole. Some galaxies (such as that shown in blue in
Fig. 10) undergo large infall and star formation events that
can cause such a track to double-back on itself and other-
wise deviate from a ‘smooth’ path (see also Calura & Menci
2009). However, our chosen galaxy provides a good example
of the general chemical evolution undergone by MW-type
galaxies in our model.
Fig. 14 shows the evolution from z = 7 to 0 of the
mass, SFR, iron abundance, total metallicity, and complete
set of heavy element enhancements for this example MW-
type galaxy, when using the power-law DTD. The different
components of the galaxy (stellar disc, cold gas, hot gas,
and ejecta reservoir) are coloured according to the legend.18
Note that Fig. 14 shows the average chemical composition
of a whole galaxy component at any given time.
Fig. 14 highlights the dependence of an element’s evo-
lution on the mode of its release, namely SNe-II, SNe-Ia or
AGB winds. Those elements that are predominantly pro-
duced in massive SNe-II (O, Ne and Mg) show a similar
decline in their enhancement with cosmic time, as we would
expect for a slowly declining SFR and a delayed enrichment
of iron. These light α elements also show lower enhance-
ments in the cold gas than in the stellar disc for this reason.
The heavier α elements (Si, S and Ca) are produced mainly
in lower-mass SNe-II, and also have a greater contribution
from SNe-Ia. They are therefore released into the ISM later
than the lighter α elements, showing a gradual increase in
enhancement with time (at a decreasing rate), and higher
enhancements in the gas than in the stars while gas fractions
are high. Nitrogen, an element with a dominant contribution
from (delayed) AGB winds at low metallicity, shows a strong
increase in [N/Fe] at the onset of AGB wind enrichment (at
z ∼ 4 for this galaxy), followed by a more gradual increase
thereafter. Finally, the drop in [C/Fe] between z ∼ 3 and 4 is
due to a decrease in the C/Fe ratio in the ejecta of SNe-II at
Zinit ∼ 0.004 compared to other metallicities. The increase
in this ratio at higher metallicities, along with a significant
contribution to C from AGB winds, casues the sharp rise in
[C/Fe] shortly after. This is a specific property of the P98
SN-II yields. When using the CL04 SN-II yields, the [C/Fe]
evolution follows that of the light α elements more closely.
To conclude this section, we can say that our new GCE
implementation is able to reproduce the [O/Fe] distribu-
18 For clarity, the bulge component is not plotted in Fig. 14. A
small bulge of 4.8 × 108M⊙ is formed via a very minor merger
(68:1 ratio) in this galaxy at z ∼ 8.5, without any accompanying
disturbance of the stellar disc. The bulge inherited the chemical
composition of the satellite’s stars at that time.
Figure 15. Three example SFHs from our model elliptical sam-
ple. The different colours correspond to different stellar masses
at z = 0 (see legend). The points represent the sum of the SFRs
from all progenitors at every output snapshot of the simulation.
Low-mass ellipticals tend to have longer star-formation timescales
than high-mass ellipticals in our model.
tion for G dwarfs in the MW disc if there is only a mi-
nor prompt component of SNe-Ia (i.e. 50 per cent within
∼ 400 Myrs). Our NG set-up (narrow Gaussian DTD, de-
layed SNe-Ia only) and PL set-up (power-law DTD, 48
per cent of SNe-Ia exploding within ∼ 400 Myrs) therefore
reproduce the observed high-[O/Fe] tail best. However, the
power-law DTD achieves this whilst assuming a more realis-
tic fraction of prompt SNe-Ia. Our new GCE implementation
also allows us to examine, in detail, the chemical evolution
undergone by individual galaxies, which can help us explain
the features seen in the sample as a whole.
6.3 Elliptical galaxies
The change in various element ratios as a function
of velocity dispersion or M∗ in ellipticals can also
provide insight into the chemical evolution of galax-
ies. It has been observed that α enhancements in-
crease with M∗ (e.g. Graves, Faber & Schiavon 2009;
Thomas et al. 2010; Johansson, Thomas & Maraston 2012;
Conroy, Graves & van Dokkum 2013). This has been mainly
attributed to massive ellipticals undergoing the majority of
their star formation at higher redshifts and over shorter
timescales. The stars in these galaxies are therefore likely to
be deficient in iron, as they were formed before a significant
number of SNe-Ia could enrich the star-forming gas. Less
massive ellipticals, on the other hand, are believed to form
a larger fraction of their stars later, from gas that has had
time to be more enriched with iron. These galaxies should
therefore have lower stellar α enhancements.
Previous GCE models, working within a hierarchi-
cal merging scenario, have found it difficult to repro-
duce this trend between stellar mass and α enhance-
ment, without invoking either a variable or adapted
IMF, morphologically-dependent star formation efficiencies
(SFEs), or additional prescriptions to increase star for-
mation at high redshift (e.g. Thomas, Greggio & Bender
1999; Thomas 1999; Nagashima et al. 2005b; Pipino et al.
2009b; Calura & Menci 2009; Arrigoni et al. 2010a,b;
Calura & Menci 2011).
We select z = 0 elliptical galaxies by bulge-to-mass ratio
c 0000 RAS, MNRAS 000, 000–000
17. Modelling element abundances 17
Figure 16. The M∗-age relation for our model elliptical galaxies.
Greyscale denotes the number density of galaxies. Model ages
are weighted by their r-band luminosity. A linear fit to the same
relation for the SDSS-DR4 from JTM12 is given by the solid
orange line, with the 1σ spread given by dotted orange lines. Our
mass-age-selected sub-sample is made up of model galaxies that
lie within one standard deviation (±0.222 dex) of the observed
mass-age relation.
and (g-r) colour, such that Mbulge/(Mbulge + Mdisc) 0.7
and (g-r) 0.051 log(M∗) + 0.14, to form a sample of ∼
8700 galaxies. These cuts are chosen to match the selection
criteria used to obtain the sample of SDSS-DR7 ellipticals
shown as green points in Fig. 19. The (g-r) colour cut also
nicely separates the red sequence from the blue cloud in our
model at z = 0. Our model sample includes type 0, 1 and 2
galaxies (see §5.3).
Fig. 15 shows the SFHs of three example galaxies from
our model elliptical sample. In this case, the sum of the
SFRs from all progenitors at any given snapshot are plotted,
rather than the SFRs from only the main progenitors. We
can see that the lowest-mass elliptical (blue) has a more
extended SFH than the highest-mass elliptical (red). This
is the case in general for our model elliptical sample (see
also De Lucia et al. 2006). We can also see that the two
most massive ellipticals in Fig. 15 (red and green) had their
star formation shut-down after a merger-induced starburst
at ∼ 5 and ∼ 3 Gyrs lookback time, respectively.
6.3.1 The mass-age relation
Before discussing element enhancements, we first show the
M∗-age relation for our model elliptical sample in Fig. 16.
Also shown is a fit to the luminosity-weighted mass-age rela-
tion from the Johansson, Thomas & Maraston (2012, here-
after JTM12) sample (solid orange line) and its 1σ scatter
(dotted orange lines). The ages of model galaxies are r-band
luminosity weighted in this plot, in order to make a fairer
comparison with the observations. For the observed rela-
tion, we have used the stellar masses taken directly from
the SDSS-DR7 catalogue19
. This is also the case for all sub-
sequent plots showing data from the JTM12 sample.
It is known that semi-analytic models tend to produce
too many old, red, dwarf galaxies by z = 0 compared to
observations (e.g. Weinmann et al. 2006; Guo et al. 2011),
as can be seen by comparing the model and observations
in Fig. 16. This is caused not just by the strong stripping
of gas from satellites, but also by the strong SN feedback
required to match the observed galaxy stellar mass func-
tion. Recent work by Henriques et al. (2013) has improved
this problem to some extent, by allowing material ejected
from model galaxies at high-z to be reaccreted over longer
timescales, allowing them to form more stars at low-z, and
therefore be younger and bluer at z = 0. However, this im-
provement is not implemented into the L-Galaxies model
presented here. Therefore, in the following sections, we will
distinguish between our full elliptical model sample and a
‘mass-age-selected’ sub-sample, which includes only those
model galaxies that lie within the 1σ scatter of the observed
M∗-age relation. This is not done in order to evade the ev-
ident issues still affecting the galaxy formation model, but
rather as a means of testing the relation between mass, age
and α enhancement in our new GCE implementation.
6.3.2 [α/Fe] relations
Fig. 17 shows the M∗-[O/Fe] relation for the bulge and disc
stars of our model ellipticals at z = 0, for the three SN-Ia
DTDs we consider. Light-blue contours represent our full
elliptical sample. Dark-blue, dashed, filled contours repre-
sent out mass-age-selected sub-sample. The observed rela-
tion from the JTM12 sample is given by the solid orange
line. The slopes of the linear fits to these three relations
are given in the top left corner of each panel.20
Model ele-
ment ratios in this section have been normalised to the solar
abundances measured by Grevesse, Noels & Sauval (1996),
in accordance with the observations to which we compare.
We note here that estimates of element enhancements
from stellar population synthesis (SPS) models, such as
those used by JTM12, are found to be fairly good rep-
resentations of the true global value, and are not as bi-
ased by small younger populations as age estimates can be
(Serra & Trager 2007). It is therefore reasonable for us to
compare our model mass-weighted element enhancements
with these observations.
As with the extent of the high-[O/Fe] tail in our MW-
type sample (see §6.2.1), we can see from Fig. 17 that the
strength of the slope in the model M∗-[O/Fe] relation is
inversely proportional to the fraction of prompt SNe-Ia as-
sumed. For the BM set-up (∼ 54 per cent of SNe-Ia ex-
plode within 100 Myrs, ∼ 58 per cent within 400 Myrs),
the model slope is much flatter than observed. For the PL
set-up (∼ 23 per cent of SNe-Ia explode within 100 Myrs,
∼ 48 per cent within 400 Myrs), a positive slope is obtained,
although shallower than observed. For the NG set-up (with
no prompt component), a strong slope is obtained, with a
larger scatter.
19 Available at http://www.mpa-garching.mpg.de/SDSS/DR7
20 The model slopes have been obtained from a linear fit in the
range 10.0 log(M∗/M⊙) 12.0.
c 0000 RAS, MNRAS 000, 000–000
18. 18 Yates et al.
Figure 17. The M∗-[O/Fe] relation for the bulge and disc com-
ponents of our model elliptical sample, when using a bi-modal
(top panel), power-law (middle panel), or narrow Gaussian (bot-
tom panel) SN-Ia DTD. Light-blue contours represent our full
elliptical sample. Dark-blue, dashed, filled contours represent out
mass-age-selected sub-sample (see text and Fig. 16). Contours
represent the 68th and 95th percentiles. A linear fit to the ob-
served relation from JTM12 is given by the orange line, with its
1σ spread (dotted orange lines). The slopes of these three rela-
tions are given in the top left corner of each panel.
The increase in slope is because massive ellipticals have
shorter star-formation timescales in the model, and so de-
creasing the fraction of prompt SNe-Ia has a bigger effect on
their final iron abundance, increasing their final α enhance-
ments more than for low-mass ellipticals. The increase in
scatter at fixed mass is because older galaxies have shorter
star-formation timescales in the model, and so undergo a
greater increase in their α enhancements for the same rea-
son. This correlation between mass, age and α enhancement
can also be seen in the increasing difference between the
slope for the full elliptical sample and the mass-age-selected
sub-sample from the top to bottom panel, and also from
the age-[O/Fe] relation shown in Fig. 18 for the PL set-
Figure 18. The relation between mass-weighted age and oxygen
enhancement for our model elliptical galaxies, when using the
power-law DTD. Points show the full elliptical sample, with the
greyscale indicating the stellar mass. Dark blue, dashed contours
show the mass-age-selected sub-sample. There is a clear positive
correlation between age and [O/Fe] in our model ellipticals, both
in general and at fixed mass.
up. This result supports the canonical thinking that the
slopes in M∗-[α/Fe] relations are driven by differences in
the star-formation timescale. If correct, then our model sug-
gests there should only be a minor fraction of prompt SNe-Ia
for any given SSP (i.e. 50 per cent within ∼ 400 Myrs).
Fig. 19 shows the enhancements of all the heavy el-
ements that we track as a function of M∗ when us-
ing the power-law DTD. As in Fig. 17, light-blue con-
tours represent our full elliptical sample. Dark-blue, dashed,
filled contours represent out mass-age-selected sub-sample.
Fits to observations of ellipticals drawn from the SDSS-
DR4 (orange lines, JTM12), the SDSS-DR6 (red line,
Graves, Faber & Schiavon 2009), and the SDSS-DR7 (green
points, see below) are also shown where possible. The PL
set-up is shown here because it provides a positive slope for
the M∗-[O/Fe] relation, while also assuming a more realistic
fraction of ‘prompt’ SNe-Ia than the NG set-up.
Pleasingly, Fig. 19 shows that positive slopes are ob-
tained for all the α elements when using our PL set-up (ex-
cept for Mg, as explained below). This is again because of
the correlation between mass, age and α enhancement in our
model. The same is true for our NG set-up, but not for the
BM set-up, which has a large fraction of prompt SNe-Ia.
This is an important result, as it has been difficult previ-
ously for models to obtain positive slopes without invoking
additional physics. It should be noted that the slopes of the
different observational data shown in Fig. 19 differ substan-
tially for some element enhancements. This is mainly due to
the difference in the SPS modelling techniques used. There-
fore, it is more important that our model produces positive
slopes at all than reproduces the exact slopes of any partic-
ular observational data set.
The methodology of both JTM12 and
c 0000 RAS, MNRAS 000, 000–000
19. Modelling element abundances 19
Figure 19. Element enhancements as a function of stellar mass for the bulge and disc components of our model elliptical sample for
our PL set-up. Light-blue contours represent our full elliptical sample. Dark-blue, dashed, filled contours represent out mass-age-selected
sub-sample. For both samples, the contours show the 68th and 95th percentiles. Fits to the observed relations from the JTM12 sample
(solid orange lines, with 1σ scatter given by dotted orange lines), Graves et al. (2009) (solid red lines, with 1σ scatter given by dotted
red lines) and a newly-selected SDSS-DR7 sample (C. Conroy & G. Graves, priv. comm.) (green points) are also shown for comparison.
Graves, Faber & Schiavon (2009) is based on fitting
observed and modelled Lick absorption line indices
(e.g. Worthey 1994). JTM12 adopt the SPS models of
Thomas, Maraston & Johansson (2011b) and 18 Lick in-
dices, whereas Graves, Faber & Schiavon (2009) adopt the
models of Schiavon (2007) and use 7 Lick indices. The fits
from JTM12 are based on a sample of visually-classified,
early-type galaxies in the redshift range 0.05 < z < 0.06.
Graves, Faber & Schiavon (2009) selected red-sequence
galaxies, classified by the colour-magnitude diagram, in
the redshift range 0.04 < z < 0.08. Both samples exclude
star-forming galaxies by applying cuts to certain emission
line strengths. Stellar masses are obtained from the MPA-
JHU catalogue for the JTM12 data, and from mass-to-light
ratios obtained using the Bell et al. (2003) (g-r)-M∗/Lg
relation for the Graves, Faber & Schiavon (2009) data. The
additional observational data (green points), kindly pro-
vided by C. Conroy & G. Graves (priv. comm.), are drawn
from the SDSS-DR7, selecting galaxies in the redshift range
0.025 < z < 0.06 with bulge-to-total light ratios 0.7 and
(g-r) 0.051 log(M∗) + 0.14. These galaxies are binned by
M∗ and their stacked spectra are used to obtain element en-
hancements using the SPS models of Conroy & van Dokkum
(2012a); Conroy, Graves & van Dokkum (2013). For a de-
tailed comparison of these different methods, see §6 of
Conroy, Graves & van Dokkum (2013).
Looking at the panels in Fig. 19 individually, we can
see that the slopes of the model relations for [C/Fe] and
[N/Fe] are shallower than observed. This is discussed fur-
ther in §6.3.4. Although our PL set-up reproduces a slope of
the M∗-[O/Fe] relation for the mass-age-selected sub-sample
close to that obtained by JTM12 (as also shown in Fig. 17),
the newly-selected SDSS-DR7 data suggests a significantly
steeper slope. Steeper slopes are obtained in the model when
c 0000 RAS, MNRAS 000, 000–000
20. 20 Yates et al.
either using the Gaussian (delayed only) DTD, or when al-
lowing direct ejection of light α elements out of galaxies via
galactic winds, as explained in §6.3.3. An increase in τmin
(the start time for SN-Ia explosions, see §4.1) also slightly
increases the slope. For example, increasing τmin from 35 to
45 Myrs increases the slope of the M∗-[O/Fe] relation by
∼ 0.004 when using the power-law DTD.
Our PL set-up produces a flat M∗-[Mg/Fe] relation,
with a slope slightly shallower than the well-constrained re-
lation obtained from the SDSS-DR7 data. The SDSS-DR7
M∗-[Mg/Fe] relation, in turn, is flatter than the other ob-
servational data sets we compare to here. In our model, the
slope of the M∗-[Mg/Fe] relation is flatter than the other
light α elements because Mg is produced in greater amounts
by low-metallicity SNe-II than high-metallicity SNe-II when
using the P98 yields (compare the bottom two panels in Fig.
4). This is not the case for the CL04 SN-II yields, which pro-
duce a slope for [Mg/Fe] very similar to that of [O/Fe], due
to the negligable difference in their metallicity dependence.
Strong, positive slopes for the heavier α elements (Si,
S and Ca) are obtained for all three of the DTDs consid-
ered here when using the P98 SN-II yields. This is because
these elements are produced only in small amounts by SSPs
at low metallicity, as they are easily locked into the stellar
remnants of the most massive, low-metallicity SNe-II (see
§3.5). Low-mass elliptical galaxies, which never obtain high
stellar metallicities, therefore never produce enough Si, S
or Ca to obtain high enhancements. As the CL04 SN-II
yields do not take account of the prior stellar winds’ ef-
fect on remnant composition, the slopes produced for the
heavier α elements are very similar to those of the lighter
α elements. This means that all slopes are equally sensi-
tive to the choice of DTD when using the CL04 yields, such
that positive slopes are only obtained if a minor prompt
component of SNe-Ia is assumed. We note that the slightly
shallower slopes for M∗-[Ca/Fe] observed in the real Uni-
verse may indicate that a larger proportion of heavy α ele-
ments come from SNe-Ia than is the case in our model (see
Conroy, Graves & van Dokkum 2013).
6.3.3 Galactic winds
The slopes of the [α/Fe] relations, for all SN-Ia DTDs and
SN-II yields considered, are strengthened by introducing
metal-rich winds, which suppress the enhancements in low-
mass ellipticals. Currently, L-Galaxies does not invoke di-
rect ejection of material by SNe, instead always fully mixing
SN ejecta with the galaxy’s ISM before reheating a fraction
of this enriched gas into the CGM. However, a simple wind
model, which allows a fraction of the material and energy
ejected by SN-II explosions in the disc to be deposited di-
rectly into the hot gas, increases the slopes of the M∗-[α/Fe]
relations. This is shown for our PL set-up in Fig. 20. This
figure can be compared to the middle panel of Fig. 17.
A scheme where only SNe-II are expected to
form a collimated galactic wind is physically moti-
vated by the fact that metal-rich winds (ubiquitous
in local, star-forming galaxies) appear to be oxygen
rich, α enhanced, and occur shortly after bouts of
star formation (e.g. Martin, Kobulnicky & Heckman 2002;
Tumlinson et al. 2011). This scheme also allows the remain-
Figure 20. The M∗-[O/Fe] relation for our model elliptical sam-
ple (when using a power-law SN-Ia DTD), with the SN feedback
scheme that allows some direct ejection of light α elements out of
galaxies via galactic winds (see §6.3.3). Contours and lines are as
in Fig. 17.
Figure 21. The [Fe/H] and [O/Fe] distributions for model MW-
type galaxies (PL set-up), with the alternative wind scheme (see
§6.3.3). This can be compared to the middle panel of Fig. 12).
Although the [Fe/H] distribution is not significantly affected when
including galactic winds, there is a slight increase in the number
of low-[O/Fe] SSPs formed.
der of the mass and energy returned by disc SNe-II to mix
with and reheat cold gas.
We set the fraction of material from disc SN-II that is
directly ejected via the wind to be inversely proportional to
the cold gas surface density of the ISM through which it
must pass;
fwind = min 1.0,
Σcold
10 M⊙pc−2
−1
. (17)
A similar dependency on the gas surface density has also
been used in the smoothed-particle hydrodynamical simu-
lations of Hopkins, Quataert & Murray (2012) and in the
Galform semi-analytic model by Lagos, Lacey & Baugh
(2013) (but see Newman et al. 2012). Interestingly, our pre-
ferred characteristic gas surface density of ∼ 10 M⊙pc−2
,
below which all SN-II ejecta material is put into the wind,
is very close to that below which the SFR surface den-
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21. Modelling element abundances 21
Figure 22. The M∗-[N/O] relation for our model elliptical sample
(PL set-up). Contours and lines are as in Fig. 17, plus a fit to the
model relation when increasing the yield of nitrogen from high-
metallicity SNe-II by a factor of 1.5 (see §6.3.4) (red line). We find
that a simple (although ad hoc) increase in the nitrogen yield is
enough to obtain a strong, positive slope in this relation.
sity drops in local, spiral galaxies (e.g. Bigiel et al. 2008;
Bigiel, Leroy & Walter 2011).
This simple wind scheme lowers the stellar α enhance-
ments of low-mass ellipticals more than high-mass ellipticals,
because low-mass ellipticals tend to have lower-density ISM,
and so can dump their SN-II ejecta more efficiently into the
CGM. This does not significantly affect the [Fe/H] distribu-
tion in the discs of MW-type model galaxies, although the
number of low-[O/Fe] SSPs does increase slightly, as shown
in Fig. 21 (compare to the middle panel of Fig. 12). How-
ever, this simple wind scheme does cause a significant under-
enrichment of the ISM in low-mass star-forming galaxies by
z = 0, which steepens the slope of the model M∗-Zcold re-
lation away from that seen in observations. Therefore, al-
though we show here that metal-rich winds are a way of
strengthening positive slopes in the M∗-[α/Fe] relations of
ellipticals, we do not claim that our simple wind model can
solve all the problems of GCE modelling.
6.3.4 Carbon and Nitrogen
The case of C and N is more complicated than that of other
heavy elements, not least because N is both a primary and
secondary element. Our model produces slopes for C and N
that are flatter than for the α elements (see top two panels
in Fig. 19). This is to be expected if C and N are predomi-
nantly released in AGB winds (as they are at low metallicity
in our model), yet observations suggest that these enhance-
ments should also produce positive slopes. To further com-
pound the problem, observations by JTM12 of the M∗-[C/O]
and M∗-[N/O] relations show that these also have positive
slopes.
Fig. 22 shows the M∗-[N/O] relation for our PL model
(without additional galactic winds), along with the fit to ob-
servations from JTM12. This model relation is also flatter
than observed, and its slope increases with the amount of
prompt SNe-Ia in the DTD. We note that there is a scatter
of high-mass model galaxies with [N/O] values more simi-
lar to those observed. However, these higher-[N/O] galaxies
tend to be young for their mass in the model, whereas the
opposite is true in the observational sample.
One way to increase the slopes in both the M∗-[N/Fe]
and M∗-[N/O] relations is to assume a greater amount of N
production in high-metallicity massive stars, as suggested
by JTM12. Doing so implies a boost in secondary nitrogen
production. Given the current uncertainty in the amount of
secondary N production in stars, this could be a plausible
solution, although this is far from certain. The red line in
Fig. 22 is a fit to the full model elliptical sample when ar-
bitrarily increasing the N released by SNe-II of metallicity
0.02 by a factor of 1.5. A similar increase is also seen in
the slope of the M∗-[N/Fe] relation. Although this is an ad
hoc adjustment made to the stellar yields, it does indicate
that such a change is capable of improving the values of both
[N/Fe] and [N/O] in our model ellipticals.
When using the CL04 yields, the M∗-[C/Fe] and M∗-
[N/Fe] relations are even flatter and the M∗-[N/O] relation
has a negative slope, due to the lower production of C and N
by SNe-II that these yield tables infer. This, again, is in con-
tradiction with the observational data considered, suggest-
ing that the P98 yields, which take account of prior stellar
mass loss from massive stars (and so are more dependent on
initial mass and metallicity), produce more realistic results
in our GCE model.
To conclude this section, we reiterate that positive slopes
in the M∗-[α/Fe] relations of local elliptical galaxies can be
obtained if either a SN-Ia DTD with minor prompt compo-
nent (i.e. 50 per cent within ∼ 400 Myrs) is used, and/or
galactic winds driven by SNe-II are allowed to directly eject
metals out of galaxies.
7 CONCLUSIONS
We have implemented a new GCE model into the Munich
semi-analytic model, L-Galaxies, which accounts for the
delayed enrichment of a series of heavy elements from SNe-
II, SNe-Ia and AGB stars. We have also compared the results
of this implementation with the chemical composition of lo-
cal, star-forming galaxies, the MW stellar disc, and local,
elliptical galaxies. Our conclusions are as follows:
• The gas-phase mass-metallicity relation for local, star-
forming galaxies (when using the Bayesian, SDSS metallici-
ties of Tremonti et al. 2004) is very well reproduced by our
new model. However, we caution that both the slope and
amplitude of the observed M∗-Zg relation depend strongly
of the metallicity diagnostic chosen (e.g. Kewley & Ellison
2008). The stellar components of low-mass, star-forming
galaxies tend to be more metal-rich in our model than ob-
served.
• The [Fe/H] distribution of G dwarfs in the MW disc is
reasonably reproduced by our model, for all forms of SN-
Ia DTD we consider. However, the high-[O/Fe] tail in the
MW [O/Fe] distribution is best reproduced when using a
SN-Ia DTD with a minor prompt component (i.e. 50 per
cent within ∼ 400 Myrs), such as a Gaussian DTD centered
on ∼ 1 Gyr, or a power-law DTD with slope ∼ −1.12 and
τmin 35 Myrs.
• Positive slopes in the M∗-[α/Fe] relations of local, el-
liptical galaxies are also obtained when assuming a minor
prompt component (i.e. 50 per cent within ∼ 400 Myrs).
The strength of the slope is inversely proportional to the
c 0000 RAS, MNRAS 000, 000–000