Evidence for reflected_lightfrom_the_most_eccentric_exoplanet_knownSérgio Sacani
Planets in highly eccentric orbits form a class of objects not seen within our Solar System. The most extreme case known amongst these objects is the planet orbiting HD 20782, with an orbital period of 597 days and an eccentricity of 0.96. Here we present new data and analysis for this system as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS). We obtained CHIRON spectra to perform an independent estimation of the fundamental stellar parameters. New radial velocities from AAT and PARAS observations during periastron passage greatly improve our knowledge of the eccentric nature of the orbit. The combined analysis of our Keplerian orbital and Hipparcos astrometry show that the inclination of the planetary orbit is > 1.22◦, ruling out stellar masses for the companion. Our long-term robotic photometry show that the star is extremely stable over long timescales. Photometric monitoring of the star during predicted transit and periastron times using MOST rule out a transit of the planet and reveal evidence of phase variations during periastron. These possible photometric phase variations may be caused by reflected light from the planet’s atmosphere and the dramatic change in star–planet separation surrounding the periastron passage.
This document summarizes the results of a deep near-infrared survey of the Carina Nebula complex using the HAWK-I instrument on the VLT. The survey imaged an area of 0.36 square degrees down to magnitudes of J=23, H=22, and Ks=21, detecting over 600,000 infrared sources. Color-magnitude diagrams of the sources were analyzed to determine properties of the low-mass stellar population such as ages and masses. The survey found that about 3200 sources have masses above 1 solar mass, consistent with expectations from the initial mass function. It also found that about half of the young stars in Carina are in a widely distributed, non-clustered configuration. Six
We discovered two transient events in the Kepler eld with light curves that strongly suggest they
are type II-P supernovae. Using the fast cadence of the Kepler observations we precisely estimate
the rise time to maximum for KSN2011a and KSN2011d as 10.50:4 and 13.30:4 rest-frame days
respectively. Based on ts to idealized analytic models, we nd the progenitor radius of KSN2011a
(28020 R) to be signicantly smaller than that for KSN2011d (49020 R) but both have similar
explosion energies of 2.00:3 1051 erg.
The rising light curve of KSN2011d is an excellent match to that predicted by simple models of
exploding red supergiants (RSG). However, the early rise of KSN2011a is faster than the models
predict possibly due to the supernova shockwave moving into pre-existing wind or mass-loss from the
RSG. A mass loss rate of 10 4 M yr 1 from the RSG can explain the fast rise without impacting
the optical
ux at maximum light or the shape of the post-maximum light curve.
No shock breakout emission is seen in KSN2011a, but this is likely due to the circumstellar inter-
action suspected in the fast rising light curve. The early light curve of KSN2011d does show excess
emission consistent with model predictions of a shock breakout. This is the rst optical detection of
a shock breakout from a type II-P supernova.
Evidence for the_thermal_sunyaev-zeldovich_effect_associated_with_quasar_feed...Sérgio Sacani
Using a radio-quiet subsample of the Sloan Digital Sky Survey spectroscopic quasar
catalogue, spanning redshifts 0.5–3.5, we derive the mean millimetre and far-infrared
quasar spectral energy distributions (SEDs) via a stacking analysis of Atacama Cosmology
Telescope and Herschel-Spectral and Photometric Imaging REceiver data. We
constrain the form of the far-infrared emission and find 3σ–4σ evidence for the thermal
Sunyaev-Zel’dovich (SZ) effect, characteristic of a hot ionized gas component with
thermal energy (6.2 ± 1.7) × 1060 erg. This amount of thermal energy is greater than
expected assuming only hot gas in virial equilibrium with the dark matter haloes of
(1 − 5) × 1012h
−1M that these systems are expected to occupy, though the highest
quasar mass estimates found in the literature could explain a large fraction of this
energy. Our measurements are consistent with quasars depositing up to (14.5±3.3) τ
−1
8
per cent of their radiative energy into their circumgalactic environment if their typical
period of quasar activity is τ8 × 108 yr. For high quasar host masses, ∼ 1013h
−1M,
this percentage will be reduced. Furthermore, the uncertainty on this percentage is
only statistical and additional systematic uncertainties enter at the 40 per cent level.
The SEDs are dust dominated in all bands and we consider various models for dust
emission. While sufficiently complex dust models can obviate the SZ effect, the SZ
interpretation remains favoured at the 3σ–4σ level for most models.
The physical conditions_in_a_pre_super_star_cluster_molecular_cloud_in_the_an...Sérgio Sacani
The document summarizes a study of an extreme molecular cloud in the Antennae galaxies that has properties consistent with forming a globular cluster. ALMA observations reveal a cloud with a radius of 24 pc and mass greater than 5 million solar masses. While capable of forming a globular cluster, a lack of associated thermal radio emission indicates star formation has not yet begun to alter the environment, suggesting the cloud is in an early stage of evolution. For the cloud to be confined as observed, an external pressure over 10,000 times greater than typical interstellar pressure is required, supporting the theory that high pressures are needed to form globular clusters in extreme environments like mergers.
This document describes the Sloan Low-mass Wide Pairs of Kinematically Equivalent Stars (SLoWPoKES) catalog, which contains 1342 very wide (projected separation >500 AU), low-mass (at least one mid-K to mid-M dwarf component) common proper motion pairs identified from the Sloan Digital Sky Survey. The catalog was constructed using astrometry, photometry, and proper motions to identify pairs with a probability of chance alignment ≤0.05. The catalog is intended to be a resource for detailed study of low-mass binary star systems and preliminary results describe the properties and characteristics of the wide, low-mass pairs.
Evidence for reflected_lightfrom_the_most_eccentric_exoplanet_knownSérgio Sacani
Planets in highly eccentric orbits form a class of objects not seen within our Solar System. The most extreme case known amongst these objects is the planet orbiting HD 20782, with an orbital period of 597 days and an eccentricity of 0.96. Here we present new data and analysis for this system as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS). We obtained CHIRON spectra to perform an independent estimation of the fundamental stellar parameters. New radial velocities from AAT and PARAS observations during periastron passage greatly improve our knowledge of the eccentric nature of the orbit. The combined analysis of our Keplerian orbital and Hipparcos astrometry show that the inclination of the planetary orbit is > 1.22◦, ruling out stellar masses for the companion. Our long-term robotic photometry show that the star is extremely stable over long timescales. Photometric monitoring of the star during predicted transit and periastron times using MOST rule out a transit of the planet and reveal evidence of phase variations during periastron. These possible photometric phase variations may be caused by reflected light from the planet’s atmosphere and the dramatic change in star–planet separation surrounding the periastron passage.
This document summarizes the results of a deep near-infrared survey of the Carina Nebula complex using the HAWK-I instrument on the VLT. The survey imaged an area of 0.36 square degrees down to magnitudes of J=23, H=22, and Ks=21, detecting over 600,000 infrared sources. Color-magnitude diagrams of the sources were analyzed to determine properties of the low-mass stellar population such as ages and masses. The survey found that about 3200 sources have masses above 1 solar mass, consistent with expectations from the initial mass function. It also found that about half of the young stars in Carina are in a widely distributed, non-clustered configuration. Six
We discovered two transient events in the Kepler eld with light curves that strongly suggest they
are type II-P supernovae. Using the fast cadence of the Kepler observations we precisely estimate
the rise time to maximum for KSN2011a and KSN2011d as 10.50:4 and 13.30:4 rest-frame days
respectively. Based on ts to idealized analytic models, we nd the progenitor radius of KSN2011a
(28020 R) to be signicantly smaller than that for KSN2011d (49020 R) but both have similar
explosion energies of 2.00:3 1051 erg.
The rising light curve of KSN2011d is an excellent match to that predicted by simple models of
exploding red supergiants (RSG). However, the early rise of KSN2011a is faster than the models
predict possibly due to the supernova shockwave moving into pre-existing wind or mass-loss from the
RSG. A mass loss rate of 10 4 M yr 1 from the RSG can explain the fast rise without impacting
the optical
ux at maximum light or the shape of the post-maximum light curve.
No shock breakout emission is seen in KSN2011a, but this is likely due to the circumstellar inter-
action suspected in the fast rising light curve. The early light curve of KSN2011d does show excess
emission consistent with model predictions of a shock breakout. This is the rst optical detection of
a shock breakout from a type II-P supernova.
Evidence for the_thermal_sunyaev-zeldovich_effect_associated_with_quasar_feed...Sérgio Sacani
Using a radio-quiet subsample of the Sloan Digital Sky Survey spectroscopic quasar
catalogue, spanning redshifts 0.5–3.5, we derive the mean millimetre and far-infrared
quasar spectral energy distributions (SEDs) via a stacking analysis of Atacama Cosmology
Telescope and Herschel-Spectral and Photometric Imaging REceiver data. We
constrain the form of the far-infrared emission and find 3σ–4σ evidence for the thermal
Sunyaev-Zel’dovich (SZ) effect, characteristic of a hot ionized gas component with
thermal energy (6.2 ± 1.7) × 1060 erg. This amount of thermal energy is greater than
expected assuming only hot gas in virial equilibrium with the dark matter haloes of
(1 − 5) × 1012h
−1M that these systems are expected to occupy, though the highest
quasar mass estimates found in the literature could explain a large fraction of this
energy. Our measurements are consistent with quasars depositing up to (14.5±3.3) τ
−1
8
per cent of their radiative energy into their circumgalactic environment if their typical
period of quasar activity is τ8 × 108 yr. For high quasar host masses, ∼ 1013h
−1M,
this percentage will be reduced. Furthermore, the uncertainty on this percentage is
only statistical and additional systematic uncertainties enter at the 40 per cent level.
The SEDs are dust dominated in all bands and we consider various models for dust
emission. While sufficiently complex dust models can obviate the SZ effect, the SZ
interpretation remains favoured at the 3σ–4σ level for most models.
The physical conditions_in_a_pre_super_star_cluster_molecular_cloud_in_the_an...Sérgio Sacani
The document summarizes a study of an extreme molecular cloud in the Antennae galaxies that has properties consistent with forming a globular cluster. ALMA observations reveal a cloud with a radius of 24 pc and mass greater than 5 million solar masses. While capable of forming a globular cluster, a lack of associated thermal radio emission indicates star formation has not yet begun to alter the environment, suggesting the cloud is in an early stage of evolution. For the cloud to be confined as observed, an external pressure over 10,000 times greater than typical interstellar pressure is required, supporting the theory that high pressures are needed to form globular clusters in extreme environments like mergers.
This document describes the Sloan Low-mass Wide Pairs of Kinematically Equivalent Stars (SLoWPoKES) catalog, which contains 1342 very wide (projected separation >500 AU), low-mass (at least one mid-K to mid-M dwarf component) common proper motion pairs identified from the Sloan Digital Sky Survey. The catalog was constructed using astrometry, photometry, and proper motions to identify pairs with a probability of chance alignment ≤0.05. The catalog is intended to be a resource for detailed study of low-mass binary star systems and preliminary results describe the properties and characteristics of the wide, low-mass pairs.
The document presents observations of the starburst galaxy NGC 253 using near-infrared imaging and spectroscopy as well as mid-infrared spectroscopy. The observations are used to derive physical properties of the starburst such as the star formation rate, stellar population, and evolutionary stage. Evolutionary synthesis modeling is applied to interpret the observations and show that the starburst in NGC 253 is in a late phase, has been ongoing for 20-30 million years, and is consistent with a modified Salpeter initial mass function.
Young remmants of_type_ia_supernovae_and_their_progenitors_a_study_of_snr_g19_03Sérgio Sacani
Type Ia supernovae, with their remarkably homogeneous light curves and spectra, have been used as
standardizable candles to measure the accelerating expansion of the Universe. Yet, their progenitors
remain elusive. Common explanations invoke a degenerate star (white dwarf) which explodes upon
reaching close to the Chandrasekhar limit, by either steadily accreting mass from a companion star
or violently merging with another degenerate star. We show that circumstellar interaction in young
Galactic supernova remnants can be used to distinguish between these single and double degenerate
progenitor scenarios. Here we propose a new diagnostic, the Surface Brightness Index, which can
be computed from theory and compared with Chandra and VLA observations. We use this method
to demonstrate that a double degenerate progenitor can explain the decades-long
ux rise and size
increase of the youngest known Galactic SNR G1.9+0.3. We disfavor a single degenerate scenario.
We attribute the observed properties to the interaction between a steep ejecta prole and a constant
density environment. We suggest using the upgraded VLA to detect circumstellar interaction in
the remnants of historical Type Ia supernovae in the Local Group of galaxies. This may settle the
long-standing debate over their progenitors.
Subject headings: ISM: supernova remnants | radio continuum: general | X-rays: general | bi-
naries: general | circumstellar matter | supernovae: general | ISM: individual
objects(SNR G1.9+0.3)
Periodic mass extinctions_and_the_planet_x_model_reconsideredSérgio Sacani
The 27 Myr periodicity in the fossil extinction record has been con-
firmed in modern data bases dating back 500 Myr, which is twice the time
interval of the original analysis from thirty years ago. The surprising regularity
of this period has been used to reject the Nemesis model. A second
model based on the sun’s vertical galactic oscillations has been challenged
on the basis of an inconsistency in period and phasing. The third astronomical
model originally proposed to explain the periodicity is the Planet
X model in which the period is associated with the perihelion precession
of the inclined orbit of a trans-Neptunian planet. Recently, and unrelated
to mass extinctions, a trans-Neptunian super-Earth planet has been proposed
to explain the observation that the inner Oort cloud objects Sedna
and 2012VP113 have perihelia that lie near the ecliptic plane. In this
Letter we reconsider the Planet X model in light of the confluence of the
modern palaeontological and outer solar system dynamical evidence.
Key Words: astrobiology - planets and satellites - Kuiper belt:
general - comets: general
The characterization of_the_gamma_ray_signal_from_the_central_milk_way_a_comp...Sérgio Sacani
This document analyzes the gamma-ray signal from the central Milky Way that is consistent with emission from annihilating dark matter particles. The authors re-examine Fermi data using cuts on an event parameter to improve gamma-ray maps and more easily separate components. They find the GeV excess is robust and well-fit by a 36-51 GeV dark matter particle annihilating to bottom quarks with a cross section of 1-3×10−26 cm3/s. The signal extends over 10 degrees from the Galactic Center and is spherically symmetric, disfavoring explanations from millisecond pulsars or gas interactions.
We present long-baseline Atacama Large Millimeter/submillimeter Array (ALMA) observations of
the 870 m continuum emission from the nearest gas-rich protoplanetary disk, around TW Hya, that
trace millimeter-sized particles down to spatial scales as small as 1 AU (20 mas). These data reveal
a series of concentric ring-shaped substructures in the form of bright zones and narrow dark annuli
(1{6AU) with modest contrasts (5{30%). We associate these features with concentrations of solids
that have had their inward radial drift slowed or stopped, presumably at local gas pressure maxima.
No signicant non-axisymmetric structures are detected. Some of the observed features occur near
temperatures that may be associated with the condensation fronts of major volatile species, but the
relatively small brightness contrasts may also be a consequence of magnetized disk evolution (the
so-called zonal
ows). Other features, particularly a narrow dark annulus located only 1 AU from the
star, could indicate interactions between the disk and young planets. These data signal that ordered
substructures on AU scales can be common, fundamental factors in disk evolution, and that high
resolution microwave imaging can help characterize them during the epoch of planet formation.
Keywords: protoplanetary disks | planet-disk interactions | stars: individual (TW Hydrae)
1. Chandra observations of the galaxy NGC 3351 revealed X-ray emission from its circumnuclear star-forming ring that is composed of numerous point-like sources embedded in diffuse hot gas.
2. The morphology of the X-ray emission is similar to but not identical with UV and H-alpha hot spots in the ring, which can be understood if star formation occurs through intermittent starbursts around the ring with different emissions tracing later evolutionary stages.
3. X-ray emission also extends beyond the ring, which is interpreted as outflowing gas from the ring into the disk and halo of NGC 3351, providing evidence for confined outflow near the plane but less restricted outflow perpendicular to
The puzzling source_in_ngc6388_a_possible_planetary_tidal_disruption_eventSérgio Sacani
Artigo descreve a descoberta da destruição de um planeta ao passar próximo a uma estrela do tipo anã branca presente dentro do aglomerado globular de estrelas NGC 6388. Para isso os astrônomos utilizaram um arsenal de telescópios.
Too much pasta_for_pulsars_to_spin_downSérgio Sacani
This document summarizes a study investigating why no isolated X-ray pulsars have been observed with spin periods longer than 12 seconds. The researchers suggest this is due to a highly resistive layer in the inner crust of neutron stars, which is expected to be in a state called "nuclear pasta". Nuclear pasta has an irregular structure that increases electrical resistivity, limiting the spin-down of pulsars. Modeling the long-term magnetic field evolution incorporating a resistive nuclear pasta layer successfully reproduced the observed 12 second period limit. The results provide the first potential observational evidence for the existence of nuclear pasta in neutron star crusts.
Inverse Compton cooling limits the brightness temperature of the radiating plasma to a maximum of
1011.5 K. Relativistic boosting can increase its observed value, but apparent brightness temperatures
much in excess of 1013 K are inaccessible using ground-based very long baseline interferometry (VLBI)
at any wavelength. We present observations of the quasar 3C 273, made with the space VLBI mission
RadioAstron on baselines up to 171,000 km, which directly reveal the presence of angular structure as
small as 26 µas (2.7 light months) and brightness temperature in excess of 1013 K. These measurements
challenge our understanding of the non-thermal continuum emission in the vicinity of supermassive
black holes and require a much higher Doppler factor than what is determined from jet apparent
kinematics.
Keywords: galaxies: active — galaxies: jets — radio continuum: galaxies — techniques: interferometric
— quasars: individual (3C 273)
Off nuclear star_formation_and_obscured_activity_in_the_luminous_infrared_gal...Sérgio Sacani
The document summarizes observations of the luminous infrared galaxy NGC 2623 from multiple telescopes. Hubble Space Telescope images reveal over 100 bright star clusters in a 3.2 kpc extension south of the galaxy's nucleus, making it one of the richest concentrations of clusters observed. The clusters have ages between 1-100 Myr based on their optical colors. Archival GALEX data show the extension is very bright in far-ultraviolet but less significant at longer wavelengths. Spitzer data detect [Ne V] emission, confirming the presence of an active galactic nucleus. The off-nuclear star formation corresponds to a rate of 0.1-0.2 solar masses per year, while the bulk of the infrared
A possible carbonrich_interior_in_superearth_55_cancrieSérgio Sacani
1) The document analyzes the possibility that the interior of the super-Earth exoplanet 55 Cancri e could be carbon-rich rather than oxygen-rich.
2) Models that assume an oxygen-rich interior with iron, silicates, and a water envelope cannot fully explain 55 Cancri e's mass and radius measurements. However, a carbon-rich interior containing iron, silicon carbide, and/or carbon could explain the observations without needing a volatile envelope.
3) A carbon-rich interior for 55 Cancri e is plausible given the reported carbon-rich composition of its host star, though more data is needed on the star's elemental abundances and the planet's atmosphere.
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
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
A spectroscopic sample_of_massive_galaxiesSérgio Sacani
This document describes a study of 16 massive galaxies at z ~ 2 selected from the 3D-HST spectroscopic survey based on the detection of a strong 4000 Angstrom break in their spectra. Spectroscopy and imaging from HST/WFC3 are used to determine accurate redshifts, stellar population properties, and structural parameters. The sample significantly increases the number of spectroscopically confirmed evolved galaxies at z ~ 2 with robust size measurements. The analysis populates the mass-size relation and finds it is consistent with local relations but with smaller sizes by a factor of 2-3. A model is presented where the observed size evolution is explained by quenching of increasingly larger star-forming galaxies at a rate set by
T he effect_of_orbital_configuration)_on_the_possible_climates_and_habitabili...Sérgio Sacani
This research article explores how the orbital configuration of Kepler-62f, a potentially habitable exoplanet in a five-planet system, could affect its climate and habitability. N-body simulations were used to determine the stable range of orbital eccentricities for Kepler-62f. Climate simulations using two global climate models then examined the planet's surface habitability across this range of eccentricities and for different atmospheric compositions. The simulations found multiple combinations of orbital and atmospheric parameters that could allow for surface liquid water on Kepler-62f, including higher orbital eccentricities coupled with high planetary obliquity or atmospheric CO2 levels above 3 bars.
The document describes measurements of the proper motion of the Andromeda Galaxy (M31) using Hubble Space Telescope imaging data from multiple fields observed at two epochs separated by 5-7 years. Background galaxies in the images are used as stationary reference objects to measure the displacement of thousands of M31 stars between epochs. This allows determining M31's absolute proper motion with an accuracy of 12 microarcseconds per year, providing crucial information about M31 and the Local Group's dynamics and future evolution.
We present deep optical images of the Large and Small Magellanic Clouds (LMC and SMC) using
a low cost telephoto lens with a wide field of view to explore stellar substructure in the outskirts
of the stellar disk of the LMC (r < 10 degrees from the center). These data have higher resolution
than existing star count maps, and highlight the existence of stellar arcs and multiple spiral arms in
the northern periphery, with no comparable counterparts in the South. We compare these data to
detailed simulations of the LMC disk outskirts, following interactions with its low mass companion,
the SMC. We consider interaction in isolation and with the inclusion of the Milky Way tidal field.
The simulations are used to assess the origin of the northern structures, including also the low density
stellar arc recently identified in the DES data by Mackey et al. (2015) at ∼ 15 degrees. We conclude
that repeated close interactions with the SMC are primarily responsible for the asymmetric stellar
structures seen in the periphery of the LMC. The orientation and density of these arcs can be used to
constrain the LMC’s interaction history with and impact parameter of the SMC. More generally, we
find that such asymmetric structures should be ubiquitous about pairs of dwarfs and can persist for
1-2 Gyr even after the secondary merges entirely with the primary. As such, the lack of a companion
around a Magellanic Irregular does not disprove the hypothesis that their asymmetric structures are
driven by dwarf-dwarf interactions.
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.
Lenz et al. discovered that soft particles at the nano- and microscale can form "clumpy crystals" where particles partially overlap and form regular lattices of clumps. This challenges ideas that soft materials will behave similarly to atomic and molecular systems. The discovery provides another example of how soft materials display unconventional behavior. An analysis of the satellites orbiting Andromeda found that about half are rotating coherently in a thin planar structure, providing a new constraint on galaxy formation theories. Further evidence suggests organized planar distributions of satellites may be common for nearby galaxy groups. The findings compound issues with the number of predicted versus observed satellites and suggest the structures themselves are not ancient.
The vvv survey_reveals_classical_cepheids_tracing_a_young_and_thin_stellar_di...Sérgio Sacani
Com o auxílio do telescópio VISTA instalado no Observatório do Paranal do ESO, astrônomos descobriram uma componente anteriormente desconhecida da Via Láctea. Ao mapear a localização de uma classe de estrelas que variam em brilho chamadas Cefeidas, foi descoberto um disco de estrelas jovens enterradas por trás de espessas nuvens de poeira no bojo central.
O rastreio público do ESO VISTA Variables in the Vía Láctea (VVV) [1] usa o telescópio VISTA instalado no Observatório do Paranal para obter imagens múltiplas em épocas diferentes das regiões centrais da nossa Galáxia nos comprimentos de onda do infravermelho [2]. O rastreio está descobrindo uma enorme quantidade de novos objetos, incluindo estrelas variáveis, aglomerados e estrelas em explosão (eso1101, eso1128, eso1141).
Uma equipe de astrônomos, liderada por Istvan Dékány da Pontificia Universidad Católica de Chile, utilizou dados deste rastreio, obtidos entre 2010 e 2014, para fazer uma descoberta notável — um componente anteriormente desconhecido da Via Láctea, a Galáxia que nos acolhe.
The document presents observations of the starburst galaxy NGC 253 using near-infrared imaging and spectroscopy as well as mid-infrared spectroscopy. The observations are used to derive physical properties of the starburst such as the star formation rate, stellar population, and evolutionary stage. Evolutionary synthesis modeling is applied to interpret the observations and show that the starburst in NGC 253 is in a late phase, has been ongoing for 20-30 million years, and is consistent with a modified Salpeter initial mass function.
Young remmants of_type_ia_supernovae_and_their_progenitors_a_study_of_snr_g19_03Sérgio Sacani
Type Ia supernovae, with their remarkably homogeneous light curves and spectra, have been used as
standardizable candles to measure the accelerating expansion of the Universe. Yet, their progenitors
remain elusive. Common explanations invoke a degenerate star (white dwarf) which explodes upon
reaching close to the Chandrasekhar limit, by either steadily accreting mass from a companion star
or violently merging with another degenerate star. We show that circumstellar interaction in young
Galactic supernova remnants can be used to distinguish between these single and double degenerate
progenitor scenarios. Here we propose a new diagnostic, the Surface Brightness Index, which can
be computed from theory and compared with Chandra and VLA observations. We use this method
to demonstrate that a double degenerate progenitor can explain the decades-long
ux rise and size
increase of the youngest known Galactic SNR G1.9+0.3. We disfavor a single degenerate scenario.
We attribute the observed properties to the interaction between a steep ejecta prole and a constant
density environment. We suggest using the upgraded VLA to detect circumstellar interaction in
the remnants of historical Type Ia supernovae in the Local Group of galaxies. This may settle the
long-standing debate over their progenitors.
Subject headings: ISM: supernova remnants | radio continuum: general | X-rays: general | bi-
naries: general | circumstellar matter | supernovae: general | ISM: individual
objects(SNR G1.9+0.3)
Periodic mass extinctions_and_the_planet_x_model_reconsideredSérgio Sacani
The 27 Myr periodicity in the fossil extinction record has been con-
firmed in modern data bases dating back 500 Myr, which is twice the time
interval of the original analysis from thirty years ago. The surprising regularity
of this period has been used to reject the Nemesis model. A second
model based on the sun’s vertical galactic oscillations has been challenged
on the basis of an inconsistency in period and phasing. The third astronomical
model originally proposed to explain the periodicity is the Planet
X model in which the period is associated with the perihelion precession
of the inclined orbit of a trans-Neptunian planet. Recently, and unrelated
to mass extinctions, a trans-Neptunian super-Earth planet has been proposed
to explain the observation that the inner Oort cloud objects Sedna
and 2012VP113 have perihelia that lie near the ecliptic plane. In this
Letter we reconsider the Planet X model in light of the confluence of the
modern palaeontological and outer solar system dynamical evidence.
Key Words: astrobiology - planets and satellites - Kuiper belt:
general - comets: general
The characterization of_the_gamma_ray_signal_from_the_central_milk_way_a_comp...Sérgio Sacani
This document analyzes the gamma-ray signal from the central Milky Way that is consistent with emission from annihilating dark matter particles. The authors re-examine Fermi data using cuts on an event parameter to improve gamma-ray maps and more easily separate components. They find the GeV excess is robust and well-fit by a 36-51 GeV dark matter particle annihilating to bottom quarks with a cross section of 1-3×10−26 cm3/s. The signal extends over 10 degrees from the Galactic Center and is spherically symmetric, disfavoring explanations from millisecond pulsars or gas interactions.
We present long-baseline Atacama Large Millimeter/submillimeter Array (ALMA) observations of
the 870 m continuum emission from the nearest gas-rich protoplanetary disk, around TW Hya, that
trace millimeter-sized particles down to spatial scales as small as 1 AU (20 mas). These data reveal
a series of concentric ring-shaped substructures in the form of bright zones and narrow dark annuli
(1{6AU) with modest contrasts (5{30%). We associate these features with concentrations of solids
that have had their inward radial drift slowed or stopped, presumably at local gas pressure maxima.
No signicant non-axisymmetric structures are detected. Some of the observed features occur near
temperatures that may be associated with the condensation fronts of major volatile species, but the
relatively small brightness contrasts may also be a consequence of magnetized disk evolution (the
so-called zonal
ows). Other features, particularly a narrow dark annulus located only 1 AU from the
star, could indicate interactions between the disk and young planets. These data signal that ordered
substructures on AU scales can be common, fundamental factors in disk evolution, and that high
resolution microwave imaging can help characterize them during the epoch of planet formation.
Keywords: protoplanetary disks | planet-disk interactions | stars: individual (TW Hydrae)
1. Chandra observations of the galaxy NGC 3351 revealed X-ray emission from its circumnuclear star-forming ring that is composed of numerous point-like sources embedded in diffuse hot gas.
2. The morphology of the X-ray emission is similar to but not identical with UV and H-alpha hot spots in the ring, which can be understood if star formation occurs through intermittent starbursts around the ring with different emissions tracing later evolutionary stages.
3. X-ray emission also extends beyond the ring, which is interpreted as outflowing gas from the ring into the disk and halo of NGC 3351, providing evidence for confined outflow near the plane but less restricted outflow perpendicular to
The puzzling source_in_ngc6388_a_possible_planetary_tidal_disruption_eventSérgio Sacani
Artigo descreve a descoberta da destruição de um planeta ao passar próximo a uma estrela do tipo anã branca presente dentro do aglomerado globular de estrelas NGC 6388. Para isso os astrônomos utilizaram um arsenal de telescópios.
Too much pasta_for_pulsars_to_spin_downSérgio Sacani
This document summarizes a study investigating why no isolated X-ray pulsars have been observed with spin periods longer than 12 seconds. The researchers suggest this is due to a highly resistive layer in the inner crust of neutron stars, which is expected to be in a state called "nuclear pasta". Nuclear pasta has an irregular structure that increases electrical resistivity, limiting the spin-down of pulsars. Modeling the long-term magnetic field evolution incorporating a resistive nuclear pasta layer successfully reproduced the observed 12 second period limit. The results provide the first potential observational evidence for the existence of nuclear pasta in neutron star crusts.
Inverse Compton cooling limits the brightness temperature of the radiating plasma to a maximum of
1011.5 K. Relativistic boosting can increase its observed value, but apparent brightness temperatures
much in excess of 1013 K are inaccessible using ground-based very long baseline interferometry (VLBI)
at any wavelength. We present observations of the quasar 3C 273, made with the space VLBI mission
RadioAstron on baselines up to 171,000 km, which directly reveal the presence of angular structure as
small as 26 µas (2.7 light months) and brightness temperature in excess of 1013 K. These measurements
challenge our understanding of the non-thermal continuum emission in the vicinity of supermassive
black holes and require a much higher Doppler factor than what is determined from jet apparent
kinematics.
Keywords: galaxies: active — galaxies: jets — radio continuum: galaxies — techniques: interferometric
— quasars: individual (3C 273)
Off nuclear star_formation_and_obscured_activity_in_the_luminous_infrared_gal...Sérgio Sacani
The document summarizes observations of the luminous infrared galaxy NGC 2623 from multiple telescopes. Hubble Space Telescope images reveal over 100 bright star clusters in a 3.2 kpc extension south of the galaxy's nucleus, making it one of the richest concentrations of clusters observed. The clusters have ages between 1-100 Myr based on their optical colors. Archival GALEX data show the extension is very bright in far-ultraviolet but less significant at longer wavelengths. Spitzer data detect [Ne V] emission, confirming the presence of an active galactic nucleus. The off-nuclear star formation corresponds to a rate of 0.1-0.2 solar masses per year, while the bulk of the infrared
A possible carbonrich_interior_in_superearth_55_cancrieSérgio Sacani
1) The document analyzes the possibility that the interior of the super-Earth exoplanet 55 Cancri e could be carbon-rich rather than oxygen-rich.
2) Models that assume an oxygen-rich interior with iron, silicates, and a water envelope cannot fully explain 55 Cancri e's mass and radius measurements. However, a carbon-rich interior containing iron, silicon carbide, and/or carbon could explain the observations without needing a volatile envelope.
3) A carbon-rich interior for 55 Cancri e is plausible given the reported carbon-rich composition of its host star, though more data is needed on the star's elemental abundances and the planet's atmosphere.
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
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
A spectroscopic sample_of_massive_galaxiesSérgio Sacani
This document describes a study of 16 massive galaxies at z ~ 2 selected from the 3D-HST spectroscopic survey based on the detection of a strong 4000 Angstrom break in their spectra. Spectroscopy and imaging from HST/WFC3 are used to determine accurate redshifts, stellar population properties, and structural parameters. The sample significantly increases the number of spectroscopically confirmed evolved galaxies at z ~ 2 with robust size measurements. The analysis populates the mass-size relation and finds it is consistent with local relations but with smaller sizes by a factor of 2-3. A model is presented where the observed size evolution is explained by quenching of increasingly larger star-forming galaxies at a rate set by
T he effect_of_orbital_configuration)_on_the_possible_climates_and_habitabili...Sérgio Sacani
This research article explores how the orbital configuration of Kepler-62f, a potentially habitable exoplanet in a five-planet system, could affect its climate and habitability. N-body simulations were used to determine the stable range of orbital eccentricities for Kepler-62f. Climate simulations using two global climate models then examined the planet's surface habitability across this range of eccentricities and for different atmospheric compositions. The simulations found multiple combinations of orbital and atmospheric parameters that could allow for surface liquid water on Kepler-62f, including higher orbital eccentricities coupled with high planetary obliquity or atmospheric CO2 levels above 3 bars.
The document describes measurements of the proper motion of the Andromeda Galaxy (M31) using Hubble Space Telescope imaging data from multiple fields observed at two epochs separated by 5-7 years. Background galaxies in the images are used as stationary reference objects to measure the displacement of thousands of M31 stars between epochs. This allows determining M31's absolute proper motion with an accuracy of 12 microarcseconds per year, providing crucial information about M31 and the Local Group's dynamics and future evolution.
We present deep optical images of the Large and Small Magellanic Clouds (LMC and SMC) using
a low cost telephoto lens with a wide field of view to explore stellar substructure in the outskirts
of the stellar disk of the LMC (r < 10 degrees from the center). These data have higher resolution
than existing star count maps, and highlight the existence of stellar arcs and multiple spiral arms in
the northern periphery, with no comparable counterparts in the South. We compare these data to
detailed simulations of the LMC disk outskirts, following interactions with its low mass companion,
the SMC. We consider interaction in isolation and with the inclusion of the Milky Way tidal field.
The simulations are used to assess the origin of the northern structures, including also the low density
stellar arc recently identified in the DES data by Mackey et al. (2015) at ∼ 15 degrees. We conclude
that repeated close interactions with the SMC are primarily responsible for the asymmetric stellar
structures seen in the periphery of the LMC. The orientation and density of these arcs can be used to
constrain the LMC’s interaction history with and impact parameter of the SMC. More generally, we
find that such asymmetric structures should be ubiquitous about pairs of dwarfs and can persist for
1-2 Gyr even after the secondary merges entirely with the primary. As such, the lack of a companion
around a Magellanic Irregular does not disprove the hypothesis that their asymmetric structures are
driven by dwarf-dwarf interactions.
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.
Lenz et al. discovered that soft particles at the nano- and microscale can form "clumpy crystals" where particles partially overlap and form regular lattices of clumps. This challenges ideas that soft materials will behave similarly to atomic and molecular systems. The discovery provides another example of how soft materials display unconventional behavior. An analysis of the satellites orbiting Andromeda found that about half are rotating coherently in a thin planar structure, providing a new constraint on galaxy formation theories. Further evidence suggests organized planar distributions of satellites may be common for nearby galaxy groups. The findings compound issues with the number of predicted versus observed satellites and suggest the structures themselves are not ancient.
The vvv survey_reveals_classical_cepheids_tracing_a_young_and_thin_stellar_di...Sérgio Sacani
Com o auxílio do telescópio VISTA instalado no Observatório do Paranal do ESO, astrônomos descobriram uma componente anteriormente desconhecida da Via Láctea. Ao mapear a localização de uma classe de estrelas que variam em brilho chamadas Cefeidas, foi descoberto um disco de estrelas jovens enterradas por trás de espessas nuvens de poeira no bojo central.
O rastreio público do ESO VISTA Variables in the Vía Láctea (VVV) [1] usa o telescópio VISTA instalado no Observatório do Paranal para obter imagens múltiplas em épocas diferentes das regiões centrais da nossa Galáxia nos comprimentos de onda do infravermelho [2]. O rastreio está descobrindo uma enorme quantidade de novos objetos, incluindo estrelas variáveis, aglomerados e estrelas em explosão (eso1101, eso1128, eso1141).
Uma equipe de astrônomos, liderada por Istvan Dékány da Pontificia Universidad Católica de Chile, utilizou dados deste rastreio, obtidos entre 2010 e 2014, para fazer uma descoberta notável — um componente anteriormente desconhecido da Via Láctea, a Galáxia que nos acolhe.
Know the star_know_the_planet_discovery_of_l_ate_type_companions_to_two_exopl...Sérgio Sacani
This document summarizes the discovery of additional late-type stellar companions to two exoplanet host stars, HD 2638 and 30 Ari B, using adaptive optics imaging. For both systems, the companions were found to share common proper motion with the primaries, indicating they are physically associated. The estimated orbital periods of the new companions are 130 years for HD 2638 and 80 years for 30 Ari B. This makes 30 Ari B the second confirmed quadruple star system known to host an exoplanet. The discoveries provide additional examples of how binary companions can influence exoplanet dynamics and formation.
Candels the correlation_between_galaxy_morphology_and_star_formation_activity...Sérgio Sacani
This document summarizes a study investigating the relationship between galaxy morphology and star formation activity at z ~ 2 using a sample of 1,671 galaxies from CANDELS images in the GOODS-South field. The sample separates into massive, red, passive galaxies and less massive, blue, star-forming galaxies, correlating well with morphological properties. Star-forming galaxies show a variety of morphologies including clumpy structures and bulges mixed with faint disks, while passive galaxies often have compact morphologies resembling local spheroids. Similar trends are seen in local massive galaxies, suggesting the Hubble sequence was in place by z ~ 2.
Star formation at the smallest scales; A JWST study of the clump populations ...Sérgio Sacani
We present the clump populations detected in 18 lensed galaxies at redshifts 1 to 8.5 within the lensing cluster field SMACS0723.
The recent JWST Early Release Observations of this poorly known region of the sky have revealed numerous point-like sources
within and surrounding their host galaxies, undetected in the shallower HST images. We use JWST multiband photometry and
the lensing model of this galaxy cluster to estimate the intrinsic sizes and magnitudes of the stellar clumps. We derive optical
restframe effective radii from <10 to hundreds pc and masses ranging from ∼ 105
to 109 M, overlapping with massive star
clusters in the local universe. Clump ages range from 1 Myr to 1 Gyr. We compare the crossing time to the age of the clumps
and determine that between 45 and 60 % of the detected clumps are consistent with being gravitationally bound. On average,
the dearth of Gyr old clumps suggests that the dissolution time scales are shorter than 1 Gyr. We see a significant increase in the
luminosity (mass) surface density of the clumps with redshift. Clumps in reionisation era galaxies have stellar densities higher
than star clusters in the local universe. We zoom in into single galaxies at redshift < 6 and find for two galaxies, the Sparkler and
the Firework, that their star clusters/clumps show distinctive colour distributions and location surrounding their host galaxy that
are compatible with being accredited or formed during merger events. The ages of some of the compact clusters are between
1 and 4 Gyr, e.g., globular cluster precursors formed around 9-12 Gyr ago. Our study, conducted on a small sample of galaxies,
shows the potential of JWST observations for understanding the conditions under which star clusters form in rapidly evolving
galaxies.
Sdss1133 an unsually_perssitent_transient_in_a_nearby_dwarf_galaxySérgio Sacani
This document summarizes observations of SDSS1133, an unusual transient object offset from the center of a nearby dwarf galaxy. SDSS1133 has been detected in observations spanning 63 years, and exhibits broad emission lines and strong variability. While initially classified as a supernova due to its non-detection in 2005, more recent observations over the past decade show it has rebrightened over a magnitude and displays properties consistent with both an active galactic nucleus and luminous blue variable star eruptions. Its nature remains ambiguous between an extreme example of pre-supernova mass loss or a potential candidate for a recoiling supermassive black hole.
This document summarizes a study that uses U-band photometry to determine photometric distances to young stars in the inner Galactic disk. The study focuses on the line of sight towards the Galactic longitude of 314 degrees. Photometric data is collected and calibrated using two open clusters in the field. Three groups of stars are detected at distances of 1.5, 2.5, and 5.1 kpc, which are consistent with the Carina-Sagittarius and Scutum-Crux spiral arms. The use of U-band photometry is shown to be an effective method for characterizing young star populations and making predictions about spiral structure in the Milky Way.
This pilot survey used modest aperture telescopes to image 8 nearby spiral galaxies in order to search for stellar tidal streams. Ultra-deep imaging revealed 6 previously undetected extensive (up to 30 kpc) stellar structures likely from tidally disrupted satellites. A diversity of tidal feature morphologies was found, including great circle-like streams, remote shells, and jets emerging from disks. Simulations predict tidal debris should be common and match the observed variety, providing evidence minor mergers have shaped disk galaxies since z=1.
X ray emission-from_strongly_asymmetric_circumstellar_material_in_the_remnant...Sérgio Sacani
This document summarizes a study of X-ray emission from circumstellar material (CSM) in the remnant of Kepler's supernova. The researchers used a statistical technique to isolate X-ray emission from CSM versus ejecta based on spectral characteristics. They found that most CSM is distributed along the bright north rim, but substantial amounts are also projected against the center, indicating a disk-like distribution of CSM from the progenitor system before the supernova. Hydrodynamic simulations support an AGB star companion as the origin of the asymmetric CSM. Quantitative analysis of magnesium emission identifies CSM and requires Kepler to have originated from a close binary system.
We report the discovery of spiral galaxies that are as optically luminous as elliptical brightest cluster
galaxies, with r-band monochromatic luminosity Lr = 8 14L (4:3 7:5 1044 erg s 1). These
super spiral galaxies are also giant and massive, with diameter D = 57 134 kpc and stellar mass
Mstars = 0:3 3:4 1011M. We nd 53 super spirals out of a complete sample of 1616 SDSS
galaxies with redshift z < 0:3 and Lr > 8L. The closest example is found at z = 0:089. We use
existing photometry to estimate their stellar masses and star formation rates (SFRs). The SDSS
and WISE colors are consistent with normal star-forming spirals on the blue sequence. However, the
extreme masses and rapid SFRs of 5 65M yr 1 place super spirals in a sparsely populated region
of parameter space, above the star-forming main sequence of disk galaxies. Super spirals occupy a
diverse range of environments, from isolation to cluster centers. We nd four super spiral galaxy
systems that are late-stage major mergers{a possible clue to their formation. We suggest that super
spirals are a remnant population of unquenched, massive disk galaxies. They may eventually become
massive lenticular galaxies after they are cut o from their gas supply and their disks fade.
This study analyzed high-resolution spectra of 125 compact stellar systems (CSSs) in the giant elliptical galaxy NGC 5128 to measure their radial velocities and velocity dispersions. Combining these measurements with structural parameters from imaging, dynamical masses were derived for 112 CSSs, including 89 for the first time. Two distinct sequences were found in the dynamical mass-to-light ratio vs dynamical mass plane, which can be approximated by power laws. The shallower sequence corresponds to bright globular clusters, while the steeper relation appears to be populated by objects requiring significant dark matter such as central black holes or concentrated dark matter. This suggests different formation histories for these CSSs compared to classical globular clusters in NGC 5128 and
The massive relic galaxy NGC 1277 is dark matter deficient From dynamical mod...Sérgio Sacani
According to the Λ cold dark matter (ΛCDM) cosmology, present-day galaxies with stellar masses M? > 1011 M should contain
a sizable fraction of dark matter within their stellar body. Models indicate that in massive early-type galaxies (ETGs) with M? ≈
1.5 × 1011 M, dark matter should account for ∼15% of the dynamical mass within one effective radius (1 Re) and for ∼60% within
5 Re
. Most massive ETGs have been shaped through a two-phase process: the rapid growth of a compact core was followed by the
accretion of an extended envelope through mergers. The exceedingly rare galaxies that have avoided the second phase, the so-called
relic galaxies, are thought to be the frozen remains of the massive ETG population at z & 2. The best relic galaxy candidate discovered
to date is NGC 1277, in the Perseus cluster. We used deep integral field George and Cynthia Mitchel Spectrograph (GCMS) data to
revisit NGC 1277 out to an unprecedented radius of 6 kpc (corresponding to 5 Re). By using Jeans anisotropic modelling, we find
a negligible dark matter fraction within 5 Re (fDM(5 Re) < 0.05; two-sigma confidence level), which is in tension with the ΛCDM
expectation. Since the lack of an extended envelope would reduce dynamical friction and prevent the accretion of an envelope, we
propose that NGC 1277 lost its dark matter very early or that it was dark matter deficient ab initio. We discuss our discovery in the
framework of recent proposals, suggesting that some relic galaxies may result from dark matter stripping as they fell in and interacted
within galaxy clusters. Alternatively, NGC 1277 might have been born in a high-velocity collision of gas-rich proto-galactic fragments,
where dark matter left behind a disc of dissipative baryons. We speculate that the relative velocities of ≈2000 km s−1
required for the
latter process to happen were possible in the progenitors of the present-day rich galaxy clusters.
The most luminous_galaxies_discovered_by_wiseSérgio Sacani
This document presents a sample of 20 extremely luminous galaxies discovered by the Wide-field Infrared Survey Explorer (WISE). Five of these galaxies have infrared luminosities exceeding 1014 solar luminosities, the highest infrared luminosity threshold yet observed. They were selected using criteria requiring weak or no detection in the first two WISE bands but strong detections in the third and fourth bands. Spectral energy distribution modeling suggests their high luminosities are powered by obscured active galactic nuclei with hot dust temperatures around 450 Kelvin. The existence of such luminous galaxies at redshifts above 3 provides constraints on the early growth of supermassive black holes through rapid accretion.
This document summarizes evidence that submillimeter galaxies (SMGs) at redshift 3-6 may be progenitors of compact quiescent galaxies observed at redshift 2. It compares properties of a sample of z~2 quiescent galaxies with a statistical sample of z>3 SMGs in the COSMOS field. It finds that the formation redshifts of the z~2 galaxies match the observed redshift distribution of z>3 SMGs. It also finds that the space densities and properties such as sizes, stellar masses, and internal velocities of the two populations are consistent with an evolutionary connection, assuming SMG starbursts have a duty cycle of 42+40 Myr. This suggests SMGs may represent an early burst
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.
A vlt flames_survey_for_massive_binaries_in_westerlund_1Sérgio Sacani
1) The authors conducted a radial velocity survey of stars in the young massive cluster Westerlund 1 to search for a potential pre-supernova companion to the magnetar CXO J1647-10.2-455216 located within the cluster.
2) They identified a candidate star, Wd1-5, that has anomalous velocities compared to other stars in the cluster, suggesting it was impacted by the supernova that created the magnetar.
3) Analysis of Wd1-5 found evidence of chemical enrichment that is difficult to explain by single star evolution, but could be explained if Wd1-5 was once part of a close binary system where it accreted material from
A Neutron Star with a Massive Progenitor in Westerlund 1GOASA
1) The authors conducted a radial velocity survey of stars in the young massive cluster Westerlund 1 to search for a potential pre-supernova companion to the magnetar CXO J1647-10.2-455216 located within the cluster.
2) They identified a candidate star, Wd1-5, that has anomalous velocities compared to other stars in the cluster, suggesting it was impacted by the supernova of the magnetar's progenitor star.
3) Analysis of Wd1-5 found evidence of chemical enrichment that is difficult to explain by single star evolution, suggesting it was part of a binary system where it accreted material from the magnetar's progenitor prior to its
This document summarizes a study that identified 195 compact elliptical galaxies across different environments using data from optical and ultraviolet sky surveys. The researchers constructed the sample by selecting galaxies that were outliers from the universal color-magnitude relation and had small sizes and high stellar velocity dispersions based on spectral modeling. They found that 7 of the galaxies were isolated, not belonging to any known galaxy groups. For these isolated galaxies, the researchers identified possible host galaxies located up to 3.3 Mpc away. The stellar populations of the isolated compact elliptical galaxies were found to be similar to those in galaxy groups and clusters, suggesting a common formation mechanism.
A 9-Month Hubble Space Telescope Near-UV Survey of M87. II. A Strongly Enhanc...Sérgio Sacani
The 135 classical novae that we have discovered in M87 with two Hubble Space Telescope imaging
surveys appear to be strongly concentrated along that galaxy’s jet. Detailed simulations show that the
likelihood that this distribution occurred by chance is of order 0.3%. The novae near the jet display
outburst characteristics (peak luminosities, colors and decline rates) that are indistinguishable from
novae far from the jet. We explore whether the remarkable nova distribution could be caused by the
jet’s irradiation of the hydrogen-rich donors in M87’s cataclysmic binaries. This explanation, and
others extant in the literature which rely on increased binary mass transfer rates, fail by orders of
magnitude in explaining the enhanced nova rate near the jet. An alternate explanation is the presence
of a genuine surplus of nova binary systems near the jet, perhaps due to jet-induced star formation.
This explanation fails to explain the lack of nova enhancement along M87’s counterjet. The enhanced
rate of novae along M87’s jet is now firmly established, and unexplained.
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
Similar to Confirmation of hostless_type_ia_supernovae_using_hubble_space_telescope_imaging (20)
Compositions of iron-meteorite parent bodies constrainthe structure of the pr...Sérgio Sacani
Magmatic iron-meteorite parent bodies are the earliest planetesimals in the Solar System,and they preserve information about conditions and planet-forming processes in thesolar nebula. In this study, we include comprehensive elemental compositions andfractional-crystallization modeling for iron meteorites from the cores of five differenti-ated asteroids from the inner Solar System. Together with previous results of metalliccores from the outer Solar System, we conclude that asteroidal cores from the outerSolar System have smaller sizes, elevated siderophile-element abundances, and simplercrystallization processes than those from the inner Solar System. These differences arerelated to the formation locations of the parent asteroids because the solar protoplane-tary disk varied in redox conditions, elemental distributions, and dynamics at differentheliocentric distances. Using highly siderophile-element data from iron meteorites, wereconstruct the distribution of calcium-aluminum-rich inclusions (CAIs) across theprotoplanetary disk within the first million years of Solar-System history. CAIs, the firstsolids to condense in the Solar System, formed close to the Sun. They were, however,concentrated within the outer disk and depleted within the inner disk. Future modelsof the structure and evolution of the protoplanetary disk should account for this dis-tribution pattern of CAIs.
Signatures of wave erosion in Titan’s coastsSérgio Sacani
The shorelines of Titan’s hydrocarbon seas trace flooded erosional landforms such as river valleys; however, it isunclear whether coastal erosion has subsequently altered these shorelines. Spacecraft observations and theo-retical models suggest that wind may cause waves to form on Titan’s seas, potentially driving coastal erosion,but the observational evidence of waves is indirect, and the processes affecting shoreline evolution on Titanremain unknown. No widely accepted framework exists for using shoreline morphology to quantitatively dis-cern coastal erosion mechanisms, even on Earth, where the dominant mechanisms are known. We combinelandscape evolution models with measurements of shoreline shape on Earth to characterize how differentcoastal erosion mechanisms affect shoreline morphology. Applying this framework to Titan, we find that theshorelines of Titan’s seas are most consistent with flooded landscapes that subsequently have been eroded bywaves, rather than a uniform erosional process or no coastal erosion, particularly if wave growth saturates atfetch lengths of tens of kilometers.
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-
�
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.
(June 12, 2024) Webinar: Development of PET theranostics targeting the molecu...Scintica Instrumentation
Targeting Hsp90 and its pathogen Orthologs with Tethered Inhibitors as a Diagnostic and Therapeutic Strategy for cancer and infectious diseases with Dr. Timothy Haystead.
TOPIC OF DISCUSSION: CENTRIFUGATION SLIDESHARE.pptxshubhijain836
Centrifugation is a powerful technique used in laboratories to separate components of a heterogeneous mixture based on their density. This process utilizes centrifugal force to rapidly spin samples, causing denser particles to migrate outward more quickly than lighter ones. As a result, distinct layers form within the sample tube, allowing for easy isolation and purification of target substances.
PPT on Alternate Wetting and Drying presented at the three-day 'Training and Validation Workshop on Modules of Climate Smart Agriculture (CSA) Technologies in South Asia' workshop on April 22, 2024.
Mechanisms and Applications of Antiviral Neutralizing Antibodies - Creative B...Creative-Biolabs
Neutralizing antibodies, pivotal in immune defense, specifically bind and inhibit viral pathogens, thereby playing a crucial role in protecting against and mitigating infectious diseases. In this slide, we will introduce what antibodies and neutralizing antibodies are, the production and regulation of neutralizing antibodies, their mechanisms of action, classification and applications, as well as the challenges they face.
CLASS 12th CHEMISTRY SOLID STATE ppt (Animated)eitps1506
Description:
Dive into the fascinating realm of solid-state physics with our meticulously crafted online PowerPoint presentation. This immersive educational resource offers a comprehensive exploration of the fundamental concepts, theories, and applications within the realm of solid-state physics.
From crystalline structures to semiconductor devices, this presentation delves into the intricate principles governing the behavior of solids, providing clear explanations and illustrative examples to enhance understanding. Whether you're a student delving into the subject for the first time or a seasoned researcher seeking to deepen your knowledge, our presentation offers valuable insights and in-depth analyses to cater to various levels of expertise.
Key topics covered include:
Crystal Structures: Unravel the mysteries of crystalline arrangements and their significance in determining material properties.
Band Theory: Explore the electronic band structure of solids and understand how it influences their conductive properties.
Semiconductor Physics: Delve into the behavior of semiconductors, including doping, carrier transport, and device applications.
Magnetic Properties: Investigate the magnetic behavior of solids, including ferromagnetism, antiferromagnetism, and ferrimagnetism.
Optical Properties: Examine the interaction of light with solids, including absorption, reflection, and transmission phenomena.
With visually engaging slides, informative content, and interactive elements, our online PowerPoint presentation serves as a valuable resource for students, educators, and enthusiasts alike, facilitating a deeper understanding of the captivating world of solid-state physics. Explore the intricacies of solid-state materials and unlock the secrets behind their remarkable properties with our comprehensive presentation.
PPT on Direct Seeded Rice presented at the three-day 'Training and Validation Workshop on Modules of Climate Smart Agriculture (CSA) Technologies in South Asia' workshop on April 22, 2024.
Microbial interaction
Microorganisms interacts with each other and can be physically associated with another organisms in a variety of ways.
One organism can be located on the surface of another organism as an ectobiont or located within another organism as endobiont.
Microbial interaction may be positive such as mutualism, proto-cooperation, commensalism or may be negative such as parasitism, predation or competition
Types of microbial interaction
Positive interaction: mutualism, proto-cooperation, commensalism
Negative interaction: Ammensalism (antagonism), parasitism, predation, competition
I. Mutualism:
It is defined as the relationship in which each organism in interaction gets benefits from association. It is an obligatory relationship in which mutualist and host are metabolically dependent on each other.
Mutualistic relationship is very specific where one member of association cannot be replaced by another species.
Mutualism require close physical contact between interacting organisms.
Relationship of mutualism allows organisms to exist in habitat that could not occupied by either species alone.
Mutualistic relationship between organisms allows them to act as a single organism.
Examples of mutualism:
i. Lichens:
Lichens are excellent example of mutualism.
They are the association of specific fungi and certain genus of algae. In lichen, fungal partner is called mycobiont and algal partner is called
II. Syntrophism:
It is an association in which the growth of one organism either depends on or improved by the substrate provided by another organism.
In syntrophism both organism in association gets benefits.
Compound A
Utilized by population 1
Compound B
Utilized by population 2
Compound C
utilized by both Population 1+2
Products
In this theoretical example of syntrophism, population 1 is able to utilize and metabolize compound A, forming compound B but cannot metabolize beyond compound B without co-operation of population 2. Population 2is unable to utilize compound A but it can metabolize compound B forming compound C. Then both population 1 and 2 are able to carry out metabolic reaction which leads to formation of end product that neither population could produce alone.
Examples of syntrophism:
i. Methanogenic ecosystem in sludge digester
Methane produced by methanogenic bacteria depends upon interspecies hydrogen transfer by other fermentative bacteria.
Anaerobic fermentative bacteria generate CO2 and H2 utilizing carbohydrates which is then utilized by methanogenic bacteria (Methanobacter) to produce methane.
ii. Lactobacillus arobinosus and Enterococcus faecalis:
In the minimal media, Lactobacillus arobinosus and Enterococcus faecalis are able to grow together but not alone.
The synergistic relationship between E. faecalis and L. arobinosus occurs in which E. faecalis require folic acid
Mending Clothing to Support Sustainable Fashion_CIMaR 2024.pdfSelcen Ozturkcan
Ozturkcan, S., Berndt, A., & Angelakis, A. (2024). Mending clothing to support sustainable fashion. Presented at the 31st Annual Conference by the Consortium for International Marketing Research (CIMaR), 10-13 Jun 2024, University of Gävle, Sweden.
Immersive Learning That Works: Research Grounding and Paths ForwardLeonel Morgado
We will metaverse into the essence of immersive learning, into its three dimensions and conceptual models. This approach encompasses elements from teaching methodologies to social involvement, through organizational concerns and technologies. Challenging the perception of learning as knowledge transfer, we introduce a 'Uses, Practices & Strategies' model operationalized by the 'Immersive Learning Brain' and ‘Immersion Cube’ frameworks. This approach offers a comprehensive guide through the intricacies of immersive educational experiences and spotlighting research frontiers, along the immersion dimensions of system, narrative, and agency. Our discourse extends to stakeholders beyond the academic sphere, addressing the interests of technologists, instructional designers, and policymakers. We span various contexts, from formal education to organizational transformation to the new horizon of an AI-pervasive society. This keynote aims to unite the iLRN community in a collaborative journey towards a future where immersive learning research and practice coalesce, paving the way for innovative educational research and practice landscapes.
Confirmation of hostless_type_ia_supernovae_using_hubble_space_telescope_imaging
1. arXiv:1505.03407v1[astro-ph.GA]13May2015
Preprint typeset using LATEX style emulateapj v. 5/2/11
CONFIRMATION OF HOSTLESS TYPE IA SUPERNOVAE USING HUBBLE SPACE TELESCOPE IMAGING
M. L. Graham1
, D. J. Sand2
, D. Zaritsky3
, C. J. Pritchet4
ABSTRACT
We present deep Hubble Space Telescope imaging at the locations of four, potentially hostless,
long-faded Type Ia supernovae (SNe Ia) in low-redshift, rich galaxy clusters that were identified in the
Multi-Epoch Nearby Cluster Survey. Assuming a steep faint-end slope for the galaxy cluster luminosity
function (αd = −1.5), our data includes all but 0.2% percent of the stellar mass in cluster galaxies
( 0.005% with αd = −1.0), a factor of 10 better than our ground-based imaging. Two of the four
SNe Ia still have no possible host galaxy associated with them (MR > −9.2), confirming that their
progenitors belong to the intracluster stellar population. The third SNe Ia appears near a faint disk
galaxy (MV = −12.2) which has a relatively high probability of being a chance alignment. A faint,
red, point source coincident with the fourth SN Ia’s explosion position (MV = −8.4) may be either
a globular cluster (GC) or faint dwarf galaxy. We estimate the local surface densities of GCs and
dwarfs to show that a GC is more likely, due to the proximity of an elliptical galaxy, but neither can
be ruled out. This faint host implies that the SN Ia rate in dwarfs or GCs may be enhanced, but
remains within previous observational constraints. We demonstrate that our results do not preclude
the use of SNe Ia as bright tracers of intracluster light at higher redshifts, but that it will be necessary
to first refine the constraints on their rate in dwarfs and GCs with deep imaging for a larger sample
of low-redshift, apparently hostless SNe Ia.
Subject headings: supernovae, galaxies: clusters
1. INTRODUCTION
Supernovae of Type Ia (SNe Ia) are the thermonu-
clear explosions of carbon-oxygen white dwarf (CO WD)
stars, commonly used as cosmological standard candles
although their progenitor scenario is not yet well under-
stood (e.g., Howell 2011). Most likely, the WD is in a
binary system with either another WD or a red giant
or main sequence star, and the explosion occurs after
merger with, or sufficient mass accretion from, the com-
panion. The explosion rate of SNe Ia is correlated with
galaxy mass and star formation rate, and most of the dis-
covered SNe Ia reside in large galaxies – but since SNe Ia
are very bright, they are also used as “cosmic light-
houses” for faint or diffuse astrophysical structures that
are difficult to assess directly. The purpose of this work is
threefold: (1) to address the utility of SNe Ia as a bright
tracer of baryons in rich galaxy clusters, (2) to confirm
that SNe Ia progenitors include truly old (> 2 Gyr) pro-
genitor systems, and (3) to investigate constraints on the
SN Ia rate in faint hosts such as dwarf galaxies and glob-
ular clusters (GC). We motivate each of these science
goals in turn.
1.1. Baryon Accounting
Understanding the growth of structure in the universe
requires a full accounting of baryonic mass, and this must
include the population of intracluster (IC) stars that were
stripped from their host galaxy and reside in the clus-
ter potential. Direct measurements of this low surface
1 Department of Astronomy, University of California, Berke-
ley, CA 94720-3411 USA
2 Physics Department, Texas Tech University, Lubbock, TX
79409
3 Steward Observatory, University of Arizona, Tucson AZ
85721
4 Department of Physics and Astronomy, University of Victo-
ria, PO Box 3055, STN CSC, Victoria BC V8W 3P6, Canada
brightness component are possible (e.g., Gonzalez et al.
2005; Zibetti et al. 2005; Montes & Trujillo 2014; De-
Maio et al. 2015), but are difficult beyond the local uni-
verse due to cosmological surface brightness dimming.
Indirect measurements of the fraction of intracluster light
(fICL) can be made using bright tracers of the under-
lying stellar population such as planetary nebulae and
novae, which has been done for the nearby Virgo and
Fornax clusters respectively (Feldmeier et al. 2004; Neill
et al. 2005). At higher redshifts a brighter tracer is re-
quired, and fICL can instead be calculated by comparing
the number of SNe Ia hosted by cluster galaxies to the
number that appear hostless and belong to the IC stellar
population.
This was first done with the Wise Observatory Optical
Transients Search (WOOTS) by Gal-Yam et al. (2003),
who found that 2 of their 7 SNe Ia in rich, low-redshift
galaxy clusters appeared to be hostless, which implied
that fICL ≈ 20%. A similar measurement was made with
the Sloan Digital Sky Survey (SDSS) by McGee & Balogh
(2010), who found that 19 of the 59 SNe Ia in low-redshift
galaxy groups appeared to be hostless, which implied
that fICL ≈ 50% for smaller-scale structures (galaxy
groups have a total mass ∼ 10% that of rich clusters).
Most recently, the Multi-Epoch Nearby Cluster Survey
(MENeaCS) from the Canada France Hawaii Telescope
(CFHT) identified four apparently hostless SNe Ia in low-
redshift massive galaxy clusters (Sand et al. 2011), which
implied that fICL = 0.16+0.13
−0.09.
This usefulness of SNe Ia as tracers of the ICL depends
on their being truly hostless. Stacked imaging from the
past surveys left 0.03−0.3% (WOOTS), 3% (SDSS), and
0.05 − 0.1% (MENeaCS) of the stellar mass in cluster
galaxies below the detection thresholds. These values are
dependent on the logarithmic faint-end slope of the lu-
minosity function, αd (i.e. the Schechter function). The
2. above results are based on αd = −1.0, which is true for
field galaxies (Blanton et al. 2003), but αd may be higher
in rich galaxy clusters (e.g., Milne et al. 2007). Adopt-
ing αd = −1.5 as an upper limit, the MENeaCS survey
estimated that 2% of the stellar mass in dwarf cluster
galaxies below detection thresholds. If the SN Ia occur-
rence rate per unit mass is equivalent in all cluster stel-
lar populations – detected galaxies (∼ 82%), undetected
dwarf galaxies ( 2%), and intracluster stars (∼ 16%) –
then for MENeaCS we expect to find that 2% of all the
discovered cluster SNe Ia (23) are hosted by faint dwarf
galaxies (∼ 0.5 SNe Ia). In this work we use deep HST
imaging at the locations of the 4 MENeaCS IC SNe Ia
to further lower the fraction of undetected mass in faint
galaxies to 0.2% (0.003–0.007% with αd = −1.0), analyze
previously undetected objects in the vicinity of 2 SNe Ia,
and discuss how our results affect the ability of IC SNe Ia
to measure fICL at higher redshifts.
1.2. SN Ia Delay Times
One path towards understanding the progenitor sce-
nario of SNe Ia is to constrain the range of possible ages
via the SN Ia delay time distribution (DTD; the time be-
tween star formation and explosion). While Type II and
Ib/c supernovae – the core collapse of massive stars – are
associated with young stellar populations, SNe Ia occur
with an explosion rate proportional to both galaxy stel-
lar mass and star formation rate (e.g., Mannucci et al.
2005; Scannapieco & Bildsten 2005; Sullivan et al. 2006).
This indicates that SNe Ia are associated with both old
and young stellar populations. The current best mea-
surements of the SN Ia DTD indicate that some SN Ia
progenitors are quite old, >2 Gyr (e.g. Maoz, Mannucci
& Nelemans 2014), which implies long-lived progenitors
and/or that the timescales for mass transfer or merger
are long.
The conclusion that at least some SN Ia require pro-
genitors that are > 2 Gyr old relies on the SN Ia rate
in rich cluster galaxies, where the majority of the stellar
population is old (e.g. Sand et al. 2012). However, there
is evidence that low levels of star formation are present
in elliptical galaxies (e.g., Yi et al. 2005; Suh et al. 2011;
Graham et al. 2012). Could it be that all SN Ia are ac-
tually from younger stellar populations? Probably not –
for example, Graham et al. (2012) show that the SN Ia
DTD result is robust to this small amount of young stars.
Even so, direct confirmation of a SN Ia progenitor in a
stellar population of purely old stars would strengthen
and support the late-time DTD constraints on the pro-
genitor scenario.
A suitable environment for this test is the population of
intracluster (IC) stars in rich galaxy clusters: the colors
and luminosities of IC red giant stars in Virgo show that
the IC stellar population is comprised of stars ≥ 2 Gyr
old (Durrell et al. 2002), and theoretical models also
suggest the ICL is comprised of old stars (e.g. Sommer-
Larsen et al. 2005; Purcell et al. 2007). All of the
apparently hostless cluster SNe discovered to date are of
Type Ia; a lack of intracluster core collapse supernovae
lends credence to the idea that the ICL is composed of
an older stellar population. In this work, we use deep
HST imaging to show that at least two of the apparently
hostless SNe Ia discovered by MENeaCS truly belong to
the IC stellar population of old stars.
1.3. SN Ia Rates in Faint Hosts
Over the past ten years, an increasing number of SN
surveys have employed an unbiased, wide-field search
strategy instead of targeting massive galaxies. This has
lead to the discovery that some types of luminous SNe
have a higher explosion rate in dwarf hosts (e.g. Neill et
al. 2011; Lunnan et al. 2014), attributed to high star
formation rates providing more progenitor stars and/or
lower metallicity leading to more luminous SNe, or per-
haps an elevated rate of binary star formation. As most
SNe Ia occur in massive galaxies, it is difficult to assess
whether they might also have an enhanced rate in dwarf
galaxies because of the large statistical uncertainty on
the rate due to the relatively low number of SNe Ia in
low-mass hosts (e.g. Quimby et al. 2012). SN surveys of
rich galaxy clusters are an efficient way to search many
low-mass galaxies at once, both due to a higher sky den-
sity of galaxies and the (putative) upturn in the faint-end
slope of the cluster luminosity function (e.g., Milne et al.
2007; Yamanoi et al. 2007). In this work we find that
one IC SN Ia may be hosted by a dwarf cluster galaxy,
and discuss the implication of this for SN Ia rates in faint
hosts.
GCs are another potential very faint host for IC SNe Ia.
No SN has ever been confirmed to be hosted by a GC,
although they are theoretically predicted to have a SN Ia
occurrence rate 1 − 10× that of elliptical galaxies due to
dynamical interactions that lead to more white dwarfs in
binary systems in GCs (e.g., Ivanova et al. 2006; Shara &
Hurley 2006; Pfahl et al. 2009). Non-detections of GCs
at the sites of ∼ 45 low-redshift SNe Ia in archival HST
images have constrained the potential rate enhancement
to 42× the rate in elliptical galaxies (Voss & Nelemans
2012; Washabaugh & Bregman 2013). In this work we
find that one IC SN Ia may be hosted by a GC, and dis-
cuss the implication of this for SN Ia rates in GCs. Since
GCs are also comprised mainly of old (5–13) Gyr stellar
populations, confirming a GC-hosted SNe Ia would also
meet our science goal of confirming SNe Ia with long (> 2
Gyr) delay times.
1.4. Paper Overview
In this work, we use the Hubble Space Telescope (HST)
Advanced Camera for Surveys (ACS) to obtain deep im-
ages in filters F606W and F814W at the locations of 4
apparently hostless SNe Ia from MENeaCS (Sand et al.
2011). These are the deepest images, and the largest
single survey sample, of IC SNe Ia locations in rich clus-
ters ever obtained and analyzed in this way. In Section
2 we present our original CFHT and new HST observa-
tions and discuss our image processing and photometric
calibrations. In Section 3 we analyze our deep stacks of
HST ACS imaging: we characterize the faint sources in
the vicinity of the SNe Ia, derive our point-source lim-
iting magnitudes, and determine the amount of cluster
stellar luminosity remaining below our detection thresh-
olds. In Section 4 we discuss the implications of these
results with respect to SN Ia progenitor ages, the rates
of SNe Ia in faint cluster objects, and the future use of
SNe Ia as tracers of the ICL. We conclude in Section 5.
All dates are given in UT and a standard flat cosmology
of ΩM = 0.3, ΩΛ = 0.7 is assumed throughout.
2. OBSERVATIONS
3. Here we describe our past observations with the Mega-
Cam imager (Boulade et al. 2003) at the Canada-France-
Hawaii Telescope (CFHT), and our new deep imaging
taken 4–5 years later with the Hubble Space Telescope
HST Advanced Camera for Surveys (ACS; Holland et al.
1998).
2.1. CFHT MENeaCS
The Multi-Epoch Nearby Cluster Survey (MENeaCS)
monitored 57 low-redshift (0.05 < z < 0.15) massive
galaxy clusters from 2008-2010 with the MegaCam in-
strument at the Canada-France-Hawaii Telescope. A to-
tal of 23 cluster SNe Ia (Sand et al. 2012) and 7 cluster
SNe II (Graham et al. 2012) were discovered. The sur-
vey strategy, spectroscopic follow-up, detection efficien-
cies, and the derivation of SN rates from MENeaCS are
presented in Sand et al. (2012), and the four intracluster
SNe Ia discovered by MENeaCS are presented in Sand et
al. (2011). For the 4 IC SNe Ia, in Table 1 we list their
MENeaCS identifier, coordinates, spectroscopic redshift,
and type as determined by the Supernova Identification
(SNID) software package (Blondin & Tonry 2007). As
described in Sand et al. (2011), these SNe Ia are all
within 1 Mpc of the brightest cluster galaxy and within
3000 km s−1
of the cluster redshift, thereby confirming
they occurred in the cluster. All four were more than
5 effective radii (i.e., > 5× the half-light radius) from
the nearest potential host galaxy in the CFHT images.
Deep stacks were made from SN-free CFHT survey im-
ages, and implanted simulated point sources were used
to constrain the limiting magnitude of any possible host
galaxy. These limits are listed for each IC SN Ia in Ta-
ble 1, along with an upper limit on the fraction of light
in low-mass cluster galaxies below our detection limit (
f(< Lmin)). Assuming a faint-end slope for the cluster
luminosity function of αd = −1.5, the fraction of stellar
mass below the detection thresholds of our CFHT deep
stacks is 2% (Sand et al. 2011).
2.2. HST ACS Imaging
To assess whether these four apparently hostless SNe Ia
truly belonged to the intracluster stellar population we
used the HST ACS to obtain deep images at their loca-
tions. We waited until >3 years after peak brightness
to obtain these images to avoid contamination from the
SN itself (this is discussed in Section 3.5). To either rule
out or classify a faint object at the SN position we re-
quired an imager that offers both sensitivity and high
resolution. Although the Wide Field Camera 3 (WFC3)
has slightly better resolution, we chose the ACS for its
higher throughput and increased sensitivity beyond 4000
˚A because most objects in galaxy clusters are red. At
our target position on the CCD we selected aperture
“WFC” because amplifier “B” on WFC1 has the low-
est read noise. We restricted our telescope orientations
to avoid possible stellar diffraction spikes coming near
our target coordinates. Because a photometric color is
necessary to classify a detected object we used two wide
filters: F606W (V -band) and F814W (I-band). We di-
vided our integration times into multiple exposures to
remove cosmic rays and used small dithers to mitigate
the effect of hot pixels, and were able to obtain all ob-
servations of a given cluster in a single visit. We provide
a summary of our HST observations in Table 2.
To make the deepest possible stacks of our HST+ACS
data, we use the Astrodrizzle software to median-combine
FLC images provided by that STScI pipeline (Gonzaga
et al. 2012). FLC files come fully reduced, drizzled,
and corrected for charge transfer efficiency by the STScI
pipeline. We use the WCS astrometry during image com-
bination. We do this for the F606W and F814W images
separately to make a deep stack for each filter that is free
of cosmic rays, and then also create a single sum-combine
image for the deepest possible stack.
2.3. HST ACS Photometric Calibrations
To obtain the apparent magnitude of a source, mf ,
where f represents filter F606W or F814W, we start
with the raw magnitude, mf,raw, for which we use
MAG AUTO from Source Extractor (Bertin & Arnouts
1996). We add a small PSF correction for point sources,
derived from the simulated sources used for the limiting
magnitudes (∼ −0.1, see Section 3.1). This is not usually
necessary with MAG AUTO but we find it is required for
the non-Gaussian PSF of the HST ACS (the Tiny Tim
PSF; Krist et al. 2011). We also apply the zeropoint,
zf = −2.5 log Pf − 21.1, where Pf is the PHOTFLAM
header keyword, representing the flux of a source with
constant Fλ which produces a count rate of 1 electron
per second (Pf has units of erg cm−2
s−1 ˚A−1
). For
our images, zF606W = 26.66 and zF814W = 26.78 mag.
To transform from the natural system and obtain the
apparent magnitude, mF , where F is the Johnson V or
Cousins I filters, we use this equation from Sirianni et al.
(2005; see their Equation 12):
mF = mf,raw +C0,F +(C1,F ×TCOL)+(C2,F ×TCOL2
)
(1)
where TCOL is the color in the targeted system; in our
case TCOL = mV − mI. We use the synthetic coefficient
values from Sirianni et al. (2005; see their Table 22), as
listed in our Table 3.
3. ANALYSIS
In this section we analyze our deep HST ACS images
at the locations of our 4 intracluster SNe Ia from ME-
NeaCS. We determine our limiting point-source magni-
tudes in Section 3.1, and derive the fraction of cluster
luminosity remaining below our detection thresholds in
Section 3.2. We present and characterize any objects
found near the SN Ia coordinates in each cluster in Sec-
tion 3.3, quantify the likelihood that detected objects are
the result of a chance alignment in Section 3.4, and rule
out the possibility of observing the evolved companion
star or lingering SN Ia emission in Section 3.5.
3.1. Point Source Limiting Magnitudes
In order to determine the limiting magnitude of our
images, we plant 5000 fake stars in each of our stacked
F606W and F814W images. These fake stars have ap-
parent magnitudes 26.0 < m < 30.0, with more stars
at fainter magnitudes, and an appropriate PSF from the
Tiny Tim model PSF generator (Krist et al. 2011). We
ensure that simulated stars are only planted in regions of
low surface brightness in order to mimic the locations of
our intracluster SNe Ia. We run Source Extractor on the
images with the simulated population of point-sources;
4. TABLE 1
CFHT Data for MENeaCS Intracluster Supernovaea
MENeaCS SN Coordinates BCG Offset Redshift Spectral CFHT Detection Limit f(< Lmin)
Identifier RA, Dec (kpc) (SNID) Type Mg, Mr αd = −1.5
Abell1650 9 13 0 12:59:01.33, −01:45:51.68 468 0.0836 Ia-norm −12.47, −13.04 0.0172
Abell2495 5 13 0 22:50:26.33, +10:54:41.70 148 0.0796 Ia-norm −11.72, −12.37 0.0127
Abell399 3 14 0 02:57:26.41, +12:58:07.63 616 0.0613 Ia-norm −12.54, −12.56 0.0138
Abell85 6 08 0 00:42:02.39, −09:26:58.00 595 0.0617 Ia-91bg −11.15, −11.68 0.0091
aFrom Table 1 in Sand et al. (2011).
TABLE 2
HST+ACS Imaging Data for MENeaCS Intracluster Supernovae
MENeaCS Orbits Observation Exposure Time (s) HST Detection Limits (mag) f(< Lmin)
Identifier Date (UT) F606W F814W F606W F814W MR αd = −1.5
Abell1650 9 13 0 5 2013-01-25 3870 6120 28.58 28.88 −9.7 0.0029
Abell2495 5 13 0 4 2013-10-04 2984 5970 28.64 28.90 −9.8 0.0026
Abell399 3 14 0 2 2013-12-04 1800 1980 28.30 28.45 −10.1 0.0035
Abell85 6 08 0 1 2013-09-18 1800 28.40 −9.2 0.0020
1 2014-09-05 1800 28.49
TABLE 3
Photometric Transformations
Natural Target C0 C1 C2 TCOL
Filter Filter mV − mI
F606W Johnson V 26.394 0.153 0.096 < 0.4
F606W Johnson V 26.331 0.340 −0.038 > 0.4
F814W Cousins I 25.489 0.041 −0.093 < 0.1
F814W Cousins I 25.496 −0.014 0.015 > 0.1
the relevant detection parameters are given in Table 4.
We visually verify that these parameters are returning
all and only real sources in the images. In Figure 1 we
plot our detection efficiency (i.e. the fraction of objects
recovered) as a function of apparent magnitude for the
F606W and F814W images of each cluster. The “limit-
ing magnitude” is defined as the magnitude at which the
detection efficiency drops to 50%, and is given for each
cluster and filter in the plot legend of Figure 1.
In Section 3.3 below, we visually identify objects be-
low the official limiting point source magnitude at the
locations of our SNe Ia in Abell 2495 and Abell 399. We
find that these objects are only detected by Source Ex-
tractor if the threshold is lowered to 1σ, which also de-
tects many peaks in the background noise and produces a
source catalog with large uncertainties in their apparent
magnitude. This is why our official limiting magnitude
– which needs to be robust because we use it to deter-
mine the fraction of cluster stellar luminosity below our
detection thresholds in Section 3.2 – is slightly brighter
than some of the sources discussed in Section 3.3. The
caveat here is that brighter, but more extended, objects
may fall below our detection threshold also – but most of
the faint cluster objects will be point-like (dwarf galaxies
and GCs).
3.2. Fraction of Undetected Cluster Light
To determine the fraction of cluster light remaining
below our point-source limiting magnitudes, we follow a
similar method to that presented by Sand et al. (2011)
for our CFHT deep-stack images, the result of which is
reproduced in the last column of Table 1.
TABLE 4
Source Extractor Parameters
for the Detection Efficiency
Parameter Value
DETECT MINAREA 3
DETECT THRESH 2
SEEING FWHM 0.08
BACK SIZE 256
BACK FILTERSIZE 5
BACK TYPE AUTO
BACKPHOTO TYPE LOCAL
Point Source Limiting Magnitudes
26.5 27.0 27.5 28.0 28.5 29.0 29.5
Simulated Apparent Magnitude
0.0
0.2
0.4
0.6
0.8
1.0
FractionRecovered
Magnitude at which the
recovery fraction < 50%
F606W F814W
A1650 28.58 28.88
A2495 28.64 28.90
A399 28.30 28.45
A85 28.40 28.49
Fig. 1.— Detection efficiencies for simulated point sources in our
HST ACS images, as described in the text (§ 3.1). Filter and
cluster are represented by color and symbol respectively, as shown
in the plot legend. The magnitude at which our detection efficiency
falls to 50% is considered our limiting magnitude.
The absolute R-band luminosity function for the
nearby Virgo cluster is modeled by Trentham & Tully
(2002) with two components, a Gaussian for the bright
5. end and a Schechter function (see their Equation 2):
N(M) = Nge−(M−Mg)2
/(2σ2
g)
+ Nd(10[−0.4(M−Md)]
)αd+1
e−10[−0.4(M−Md)]
, (2)
where N(M) is the number density of galaxies per square
Mpc per magnitude bin, M is the R-band absolute
magnitude, and Ng = 17.6, Mg = −19.5, σg = 1.6,
Nd = 3Ng, Md = −18.0, and αd = −1.03. However, the
faint-end slope is known to steepen with redshift (e.g.,
Khochfar et al. 2007), and values down to αd ≈ −1.5
have been measured for the Coma cluster (Milne et al.
2007) and most recently for Abell 85 (αd ≈ −1.6; Agulli
et al. 2014). In order to make a robust upper limit on the
amount of cluster light below our detection efficiencies,
we use αd = −1.5 from here on.
In Sand et al. (2012) the total r′
-band luminosity is
calculated for all MENeaCS clusters. We convert this
to R-band using the conversion factors from Blanton &
Roweis (2007), R = r − 0.0576 − 0.3718((r− i)− 0.2589).
Because most of the cluster light is from old stellar popu-
lations, we use the typical SDSS color of elliptical galax-
ies, r − i ∼ 0.4, from Eisenstein et al. (2001). We inte-
grate the galaxy luminosity function down to the CFHT
point-source limiting magnitudes listed in Table 1 from
Sand et al. (2011), and then normalize to the total R-
band luminosity for each cluster.
We convert the absolute R-band luminosity function
for each cluster into apparent V - and I-band using the
cluster’s redshift, the elliptical galaxy template spec-
trum from Kinney et al. (1996), and the line-of-sight
Galactic extinction for each cluster: AV,A1650 = 0.047,
AV,A2495 = 0.211, AV,A399 = 0.467, AV,A85 = 0.103,
AI,A1650 = 0.026, AI,A2495 = 0.116, AI,A399 = 0.256, and
AI,A85 = 0.057 (Schlafly & Finkbeiner 2011; Schlegel,
Finkbeiner & Davis 1998). We convert the V and I-band
luminosity function into the HST ACS natural system fil-
ters using the transformations of Sirianni et al. (2005),
as described in Section 2.3. In Table 2, we report the
point-source detection limit in absolute MR magnitudes,
and the fraction of the cluster’s R-band stellar luminosity
remaining below this limit. For all clusters we find that
< 0.2% of the stellar mass in cluster galaxies remains
below our official point-source limiting magnitude. This
result is discussed further in Section 4.
3.3. Potential Hosts in the Deep HST-ACS Images
We use the IRAF tasks GEOMAP and GEOTRAN to
co-register our CFHT images to the new, deeper HST-
ACS images. In Figures 2–5 we show the results, side by
side, for comparison. The CFHT images are comprised of
two 120 second r′
exposures, and contain the SN Ia – we
do not use our SN-free deep stacks here, because we need
the SN’s coordinates in the co-registered frames. The
HST images are our deepest stacks, the sum-combined
F606W and F814W filtered images. Green circles mark
the position of the SN in each image, with a radius equal
to 3× the positional uncertainty of the SN Ia. These posi-
tional uncertainties, listed in Table 5, are a combination
of Source Extractor’s uncertainty in the PSF centroid
for the SN in the co-registered CFHT image (using win-
dowed output parameters), and the error in GEOMAP’s
transformation between images. The dashed cyan lines
TABLE 5
Supernova Positional Uncertaintya
SN Ia PSF Centerb GEOMAPc Totald Error
Cluster ∆x ∆y ∆x ∆y ∆x ∆y Radiuse
Abell (pix) (pix) (pix) (pix) (pix) (pix) (′′)
1650 4.57 4.57 0.31 0.13 7.52 7.62 0.23′′
2495 6.55 6.31 1.81 2.00 6.42 6.46 0.34′′
399 6.15 6.00 0.63 1.56 7.76 7.82 0.31′′
85 7.39 7.21 2.57 3.52 10.41 10.15 0.40′′
aAll pixels are HST ACS pixels (0.05′′ pixel−1).
bSource Extractor’s uncertainty on the SN’s coordinates in
the CFHT image post-transformation with GEOTRAN (i.e., the
square root of the variance, the second moment of the barycenter).
cGEOMAP’s uncertainty in mapping the CFHT image to the
HST image (i.e., a systematic, the output xrms and yrms values).
dAdded in quadrature.
eAverage in x and y, ×0.05′′ pixel−1.
enclose nearby objects (sizes chosen to guide the eye).
Image information such as the cluster name, UT date of
acquisition, filters, scale bar, and compass are shown in
yellow along the bottom. These images all have a 30′′
×
30′′
field of view.
As in Sand et al. (2011), we use the dimensionless pa-
rameter R to identify whether nearby objects could be
considered as potential hosts of the SNe Ia. This param-
eter is defined in the Source Extractor manual as:
R2
= Cxxx2
r + Cyyy2
r + Cxyxryr (3)
where Cxx, Cyy, and Cxy are object ellipse parameters,
xr = xSN −xgal and yr = ySN −ygal, and R ∼ 3 describes
the isophotal limit of the galaxy (see also Sullivan et al.
2006). A supernova is typically only classified as “host-
less” if R > 5, but depending on the surface brightness
profile of the galaxy, a significant amount of the stellar
mass may reside beyond this radius (e.g., 10% for the
potential host of the SN in Abell 399, as determined in
Sand et al. 2011).
3.3.1. Abell 1650
In Figure 2, we see that the location of the SN Ia is
truly devoid of objects. We ran Source Extractor with
very relaxed parameters and still recovered no sources in
this area. Of the three nearby objects enclosed by dashed
circles in Figure 2, the SN location is R 15 away. Our
intracluster SN Ia in Abell 1650 therefore appears to be
truly hostless.
3.3.2. Abell 2495
In Figure 3 we see several sources near the location
of the SN Ia that were not apparent in the CFHT deep
stacks presented in Sand et al. (2011), but none are
within the positional uncertainty of the SN Ia. We ran
Source Extractor with very relaxed parameters and still
recovered no sources within the positional uncertainty.
In Figure 6 we show this region in detail, and identify
nearby sources A, B, C, and D. Sources A and B are
unlikely to be physically associated, as the SN Ia is R ∼
17 away from them. We discuss objects C and D in turn.
Object C is likely a part of object D, which is clumpy
and extended, as shown by the contour plot in the right-
hand image of Figure 6. However, object C is identified
by Source Extractor as an independent source at the 1σ
6. 2009-12-14
CFHT r’
Abell 1650
3.14 kpc
2.0"
N
E
r=0.5"
SN
r=0.69"
2013-01-25
HST 606W+814W
Abell 1650
3.14 kpc
2.0"
N
E
r=0.5"
SN
r=0.69"
Fig. 2.— Co-registered CFHT (left) and HST (right) images for the SN Ia in Abell 1650, as described in the text of Section 3.3.
2009-05-23
CFHT r’
Abell 2495
3.0 kpc
2.0"
N
E
SN
r=1.02"
2013-10-04
HST 606W+814W
Abell 2495
3.0 kpc
2.0"
N
E
SN
r=1.02"
Fig. 3.— Co-registered CFHT (left) and HST (right) images for the SN Ia in Abell 2495, as described in the text of Section 3.3.
level in the F814W image, with mF814W = 29.0±0.2 mag.
In the F606W image it is not officially detected by Source
Extractor, but it is just visible to the eye, and with aper-
ture photometry we estimate it to be mF606W = 29.8±0.2
mag. In both filters, object C falls below our 50% detec-
tion efficiency for Abell 2495 (see Figure 1 in Section 3.1).
The SN’s location is R 5 away from object C, which
argues against a physical association. Object C is redder
than the red sequence of Abell 2495, as shown in Figure
7, and so it is unlikely to be a cluster dwarf galaxy. The
scenarios in which object C is lingering emission from the
SN Ia or a chance alignment are discussed in Sections 3.4
and 3.5. Ultimately we find it unlikely that object C is
the host galaxy.
Object D is an extended source with semi-major and
semi-minor axes of A = 0.22′′
and B = 0.053′′
, which
leads to SN offsets of R = 4.9 and 4.1, in F606W and
F814W respectively. As R < 5, this SN Ia cannot be
considered truly hostless unless we can show that object
D is unlikely to be a cluster member. In the natural
system of HST ACS, object D is mF606W = 25.56 and
mF814W = 25.75 mag, and has a color = −0.20 mag.
7. 2009-01-27
CFHT r’
Abell 399
2.36 kpc
2.0"
N
E
r=0.93"
SN
2013-12-04
HST 606W+814W
Abell 399
2.36 kpc
2.0"
N
E
r=0.93"
SN
Fig. 4.— Co-registered CFHT (left) and HST (right) images for the SN Ia in Abell 399, as described in the text of Section 3.3.
2009-06-18
CFHT r’
Abell 85
2.38 kpc
2.0"
N
E
r=1.0"
r=1.20"
SN
2013-09-18
HST 606W+814W
Abell 85
2.38 kpc
2.0"
N
E
r=1.0"
r=1.20"
SN
G
Fig. 5.— Co-registered CFHT (left) and HST (right) images for the SN Ia in Abell 85, as described in the text of Section 3.3.
As shown in Figure 7 it consistent with a red sequence
cluster galaxy. We use Sirianni et al. (2005) to convert
this photometry into Landolt filter system and find that
object D is mV ≈ 25.6 and mI ≈ 24.5 mag. We apply
the distance modulus of Abell 2495 (µ ≈ 37.8 mag) and
find that intrinsically, object D is MV ≈ −12.2 and MI ≈
−13.3 mag. This is brighter than the limiting magnitudes
quoted for the CFHT deep stack of Abell 2495, but those
limits are for point-like sources and object D is extended
– in fact, it is just barely visible as an extended source
in Figure 3 of Sand et al. (2011).
Object D is clumpy and has an ellipticity of 0.7, which
is higher than the ellipticity of the bright red sequence
galaxies we identify in Abell 2495. Morphologically, ob-
ject D resembles an inclined disk galaxy – can we use
the disk scale length to assess whether it may be a blue
spiral galaxy at higher redshift? Disk galaxies are gen-
erally well fit by an exponential function for the flux in-
tensity as a function of radius, I(R) = I0e−R/Rd
, where
Rd is the characteristic disk scale length. We estimate
Rd 0.4′′
, with no attempt to de-project or account for
inclination. If object D is a cluster member, this corre-
8. HST 606W+814W
Abell 2495
0.75 kpc
0.5"
r=0.24"r=0.34"
SN
C
D
BA
HST 606W+814W
Abell 2495
0.75 kpc
0.5"
r=0.24"r=0.34"
SN
C
D
B
A
Fig. 6.— The HST+ACS image from the deepest stack of both filters F606W and F814W for the intracluster SN Ia in Abell 2495. The
green circle marks the position of the SN Ia, with a radius equal to 1× the positional uncertainty from Table 5. In cyan we identify nearby
objects A, B, C, and D (we cannot verify whether C is a part of D), discussed in the text. For objects A and B, the dashed cyan circle has
r = 0.24′′, representing 3× the PSF FWHM of ACS (0.08′′). For the dashed ellipse around object D we use the parameters determined by
Source Extractor for the F814W image: 3× the semi-major and -minor axes, A = 4.4 and B = 1.1 pixels (A = 0.22′′ and B = 0.053′′), and
a position angle of θ = 74 degrees (in the x-y plane). In the image at right, we include flux contours in magenta to highlight the connection
between objects C and D and the lack of low-significance sources within the SN’s positional error circle.
Fig. 7.— Color-magnitude diagram in the natural HST ACS filter
system for Abell 2495. Black points represent all sources extracted
with an apparent magnitude brighter than the 50% detection ef-
ficiencies in both F606W and F814W, as discussed in § 3.1 and
shown in Figure 1. Black points surrounded by red indicate the
galaxies used in the linear fit to the red sequence (red lines). The
blue square and circle represent objects C and D respectively (see
Figure 6).
sponds to Rd ∼ 0.6 kpc, which is roughly appropriate for
a disk galaxy. In Section 3.4 we also discuss the relatively
large probability that this is a chance alignment, but for-
mally we cannot exclude the possibility that object D is
a cluster member and the host of the SN in Abell 2495.
3.3.3. Abell 399
In Figure 4 we see a large elliptical galaxy near the lo-
cation of the SN Ia. Sand et al. (2011) describes how the
SN is > 7R from the large elliptical, and how the SN’s
and galaxy’s line-of-sight velocities differ by 3σ, indicat-
ing they are not associated. We use these HST images to
re-evaluate the parameter R from Equation 3, which de-
scribes the SN’s offset in terms of the galaxy’s isophotes.
We find that R ∼ 6 in both F606W and F814W, re-
establishing the SN as independent of the stellar popu-
lation of this large neighbor galaxy.
In Figure 4 we see a small, faint source at the center
of the green circle marking the SN Ia’s position, labeled
object F in Figure 8. Object F is detected with low sig-
nificance, but with coincidence in both the F606W and
F814W images. It is a point-like source, with a FWHM
of ∼ 3 pixels, and is offset by < 1 pixel from the SN Ia
location. Object F is therefore very likely to be physi-
cally associated with the SN Ia in Abell 399 – the small
probability of a chance alignment with a foreground star
or background host is discussed in Section 3.4. In Fig-
ure 8 we also label the next-nearest object E; it is a
clumpy extended source, but we find it far less likely to
be physically associated with the SN and so we focus our
attention on object F.
Object F is mF606W = 28.7 ± 0.3 and mF814W =
28.7 ± 0.2 mag, below our limiting magnitudes as shown
in Figure 1. Its photometry is consistent with a red se-
quence galaxy in Abell 399, which is very similar to the
red sequence shown for Abell 2495 in Figure 7. We use
Sirianni et al. (2005) to convert this photometry into the
Landolt filter system and find that object F is mV ≈ 28.8
and mI ≈ 27.4 mag. We apply the distance modulus of
Abell 399 (µ ≈ 37.2 mag) and find that intrinsically, ob-
ject F is MV ≈ −8.4 and MI ≈ −9.8 mag, and has a
color of V − I ≈ 1.4. This is also well matched to the
expected magnitude and color of a bright GC: the lu-
minosity function for GCs is a Gaussian that peaks at
MI ≈ −7.4 and has σ ≈ 1.2, and GC colors span from
MV − MI ≈ 0.7–1.5 (e.g., West et al. 2011). Although
GCs have been found distributed between galaxies in rich
9. HST 606W+814W
Abell 399
0.59 kpc
0.5"
E
F
r=0.31"
SN
Fig. 8.— The HST+ACS image from the deepest stack of both
filters F606W and F814W for the candidate intracluster SN Ia in
Abell 399; a zoom-in of Figure 4.
clusters (e.g. Peng et al. 2011; West et al. 2011), their
density drops with clustercentric radius and we would
not expect a significant number of intracluster GCs at
the location of this SN Ia, 616 kpc from the BCG. How-
ever, the presence of the nearby elliptical galaxy (Figure
4) makes the GC hypothesis more likely.
In Section 4.1, we show that the SN Ia rate enhance-
ments in dwarf galaxies or GC implied by the nature of
object F are within all existing theoretical and observa-
tional limits. If we assume that the rate per unit mass
of SNe Ia is not much larger in dwarf galaxies vs. GC
(or vice versa) – which would put a strong prior on the
nature of object F – we can estimate the expected sur-
face densities of dwarf red sequence galaxies and red GCs
at this location in order to assess which is more proba-
ble. Based on our extrapolation of the cluster luminosity
function for Abell 399 (Section 3.2), we estimate there to
be ∼ 1.5×109
L⊙ in dwarf cluster galaxies at MR > −10
mag. That is about 100–500 dwarf galaxies of 5–10 ×106
L⊙ within a clustercentric radius of ∼ 1 Mpc, or 1–5
×10−4
dwarfs kpc−2
. This would apply at any location
in the cluster, and so applies for the location of object F.
To assess whether satellites of the nearby elliptical galaxy
might raise the predicted surface density at this location,
we use the radial distribution of low-redshift, low-mass
satellite galaxies presented by Prescott et al. (2011; see
their Figure 5). The location of the SN in Abell 399 is
R ≈ 10 kpc from the center of the nearby elliptical; at
this radius Prescott et al. (2011) find that the surface
density of satellites is ∼ 7×10−6
kpc−2
. The caveat here
is that they consider only isolated primary galaxies, and
so their results represent an upper limit on the radial dis-
tribution we could expect in rich clusters. However, as
this is much lower than what we expect from the cluster
luminosity function we conclude that object F is unlikely
to be a satellite galaxy of the nearby elliptical.
We can estimate the surface density of GC from the
nearby elliptical galaxy (Figure 4), which has absolute
magnitudes of MV ≈ −19.5 and MI ≈ −20.7, and a stel-
lar mass of ∼ 7.6×109
M⊙ (Bell et al. 2003). A galaxy of
this stellar mass has between 10–100 GC within R < 50
kpc, and the surface density radial distribution for GC
is N(r) = N0r−2.4
GC kpc−2
(Zaritsky et al. 2015);
∼ 75% of the GC are internal to 10 kpc (the distance
of the SN in Abell 399 from the nearby elliptical). Nor-
malizing the radial distribution to a total of 10–100 GC
gives N ≈ 0.3−3×10−2
GC kpc−2
. Based on the GC lu-
minosity function of West et al. (2011) ∼ 84% of all GC
are below our limiting magnitudes, and so the observable
surface density at 10 kpc is lowered to 0.5 − 5 × 10−3
GC kpc−2
. This is higher than our estimated surface
density for cluster dwarf galaxies, suggesting it is more
likely to see a GC at the location of object F than a
cluster dwarf. However, as our lower limit for the GC
surface density is equal to our upper limit on the dwarf
galaxy surface density the estimates are not significantly
different enough to make a robust claim to the nature of
object F. The caveat here is that we have used a radial
distribution for all GC, but the population of red GCs
has a significantly shorter radial extent than blue GCs –
in fact, for cluster ellipticals the radial distribution of red
GCs appears to be truncated near the effective radius of
the parent galaxy (e.g., Brodie & Strader 2006).
In summary, we find that the SN Ia in Abell 399 is
likely physically associated with object F. Without any
constraints from expected SN Ia rates, we find that object
F is less likely to be a dwarf galaxy than a GC from the
nearby elliptical. We discuss the probability of chance
alignments in Section 3.4, and the possibility that object
F is lingering emission from the SN Ia in Section 3.5. We
discuss the implications of object F for SN Ia rates in
dwarf galaxies and GCs, and whether these implications
provide a prior on the nature of object F, in Section 4.1
and the impact of object F on using SN Ia as tracers of
the ICL at high-redshift in Section 4.2.
3.3.4. Abell 85
In Figure 5, we see that the location of the SN Ia ap-
pears devoid of objects. For the nearest source, labeled
object G in Figure 5, the SN is R ∼ 13 away. We
ran Source Extractor with very relaxed parameters, but
found that the few sources detected are consistent with
noise peaks (i.e., they had very low significance, their de-
tections in F814W only and were not coincident with any
F606W low-significance detections, and were not visually
confirmed in the F606W+F814W stack). We conclude
that the SN Ia in Abell 85 is truly hostless.
3.4. Probabilities of Random Line-of-Sight Alignments
In our discussion of the nature of object F in Abell
399 we estimated the surface densities of faint cluster
objects such as dwarf red sequence galaxies and GCs to
be ∼ 5×10−4
objects per kpc2
. The probability of a faint
cluster object appearing randomly within the positional
uncertainty of our IC SNe Ia is negligible, 0.0003%.
The presence of object F is not a chance alignment with
a cluster object.
We used TRILEGAL (Girardi et al. 2005) to simulate
a foreground star population in the directions of our four
fields to a limiting magnitude of mV = 29. The prob-
ability of a star appearing randomly within 0.2′′
of our
10. IC SN Ia coordinates is ≤0.02%. We judge that it is ex-
tremely unlikely that object F at the location of the SN
in Abell 399 is a foreground red star.
We used the Hubble Deep Field catalogs (Williams et
al. 1996) to simulate a population of faint objects be-
tween 25.0 < mF814W < 29.5. This is the magnitude
range in which we detect sources in our HST images but
not our CFHT images. The new sources detected near
the SN Ia locations in Abell 2495 and Abell 399 fall in this
magnitude range. We find the probability of a faint field
object randomly being within 0.31′′
and 0.34′′
, the po-
sitional uncertainties on the locations of the SNe Ia, are
∼ 2.0% and ∼ 2.5%, respectively. In our original work
∼ 2% of the cluster stellar mass in faint dwarf galaxies
was below our detection limit (Sand et al. 2011). Assum-
ing the SN Ia occurrence rate per unit mass is equivalent
in all populations (high- and low-mass galaxies, and in-
tracluster stars), this means ∼ 2% of the all MENeaCS
SNe Ia should be hosted by undetected, faint dwarf galax-
ies (∼ 0.5 out of 23 SNe Ia). We now see that this is
approximately the same chance as finding a background
galaxy within the positional uncertainty. However, ob-
ject F in Abell 399 is not just within the positional un-
certainty, but appears within 0.05′′
(1 ACS pixel) of the
SN location. The probability of random alignment with
a background object within 0.10′′
is just 0.3%. On the
other hand, if we increase the radius to 1.0′′
(i.e. the dis-
tance encompassing nearby objects for Abell 2495), the
probability of chance alignment increases to ∼ 18%.
As a final, alternative estimate we use our own source
catalogs for all four HST -ACS fields and find that the
fraction of our imaged area within R < 5 of an object is
∼ 3%. While it remains very unlikely that object F is a
chance alignment with the SN Ia in Abell 399 (Figure 8),
we cannot say the same for the objects near the SN Ia
location in Abell 2495 (Figure 6).
3.5. Limits on the SNe Ia and/or its Companion
A normal SN Ia has faded ∼ 4 magnitudes by ∼ 100
days after peak brightness. After this time the decline
is set by the decay rate of Co56
, and the SN Ia continues
to fade at ∼ 1 magnitude per 100 days in I-band, and
∼ 1.3 − 1.5 mag per 100 days in BV R (e.g. as seen
for normal twin SNe Ia 2011fe and 2011by; Graham et
al. 2015a). For a normal SN Ia such as SN 2011fe, the
intrinsic brightness at ∼ 1000 days is V ∼ −5 magnitudes
(e.g., Kerzendorf et al. 2014; Graham et al. 2015b).
Most of the flux comes from blue emission features of
[Fe II] at < 6000 ˚A (e.g., Taubenberger et al. 2015;
Graham et al. 2015b), and the late-time V − I color of a
normal SN Ia is expected to be ∼ 0. After ∼ 1000 days,
the predicted rate of decline for normal SNe Ia is even
slower (Seitenzahl et al. 2009), and so V ∼ −5 mag is a
conservative upper limit on SN Ia brightness after 1000
days.
Over-luminous SNe Ia that resemble SN 1991T have
been observed to decline more slowly. For example,
SN 1991T itself was V ∼ −10 at ∼ 600 days (Cappel-
laro et al. 1997) and SN 2000cx had a V -band slope
of ∼ 0.65 mag per 100 days at ∼ 700 days after peak
brightness (Sollerman et al. 2004), so a SN 1991T-like
event could be V −7 at 1000 days. However, none
of the MENeaCS SNe Ia were spectroscopically similar
to SN 1991T, and are furthermore unlikely to belong to
this subclass because 91T-like SNe Ia are associated with
younger stellar populations (Howell et al. 2009). Al-
though less is known about the late-time decline of sub-
luminous SNe Ia, SN 1991bg itself was already V ≈ −6
by ∼ 600 days after peak brightness (Turatto et al.
1996). Our intracluster SN Ia in Abell 85 was classified as
SN 1991bg-like, but no object is detected at its location
in the HST ACS imaging.
Could we detect the emission from a shocked compan-
ion star? For normal SNe Ia, theoretical predictions for
a non-degenerate companion shocked by the SN Ia ejecta
include an increase in temperature and luminosity, up to
103
to 104
L⊙ by 1–10 years after explosion (Pan et al.
2013; Shappee et al. 2013). Such a companion would be
blue, and have V > −4 mag, which is well below our lim-
iting magnitudes. A light echo is also likely to be blue,
similar to the color of a SN Ia at peak light, and even
fainter. In order to formally rule out the possibility that
the objects identified near the SN locations in Abell 2495
and Abell 399 are lingering emission from the SN Ia or
its binary companion, we discuss each in turn.
Abell 2495 – In Figure 6 we identify object C as a
possible point source near the location of the SN Ia in
Abell 2495. The spectrum of this SN Ia was obtained
on 2009-06-18.58 UT at Gemini Observatory as part of
the MENeaCS follow-up campaign, and we classified it
as a normal SN Ia at ∼ +3 months after peak bright-
ness. At the time of our HST ACS images obtained
on 2013-10-04, the SN Ia would be +1569 days old (4.3
years). At this time, object C is mF606W = 29.8±0.2 and
mF814W = 29.0 ± 0.2 mag, or mV ≈ 30.0 and mI ≈ 27.8
mag, in our HST ACS imaging. We apply the distance
modulus of Abell 2495 (µ ≈ 37.8 mag) and find that
intrinsically, object C is MV ≈ −7.8 and MI ≈ −10.0
magnitudes. This is both significantly brighter and red-
der than a normal SN Ia is predicted to be at ∼ 4 years.
We conclude that object C is unlikely to be the SN Ia or
an evolved companion star.
Abell 399 – In Figure 8 we identify object F as a
point source at the location of the SN Ia in Abell 399.
The classification spectrum of this SN Ia, obtained on
2008-11-28.49 UT at Gemini Observatory as part of the
MENeaCS follow-up campaign, showed it to be a normal
SN Ia at ∼ +2 weeks after peak brightness. In our HST
ACS images obtained on 2013-12-04, the SN Ia would be
+1832 days old (5 years). This object is MV ≈ −8.4
and MI ≈ −9.8 mag, has a color of V − I ≈ 1.4, both
significantly brighter and redder than a normal SN Ia is
predicted to be at extremely late times. We conclude
that object F is unlikely to be the SN Ia or an evolved
companion star.
4. DISCUSSION
Our analysis of the HST ACS images at the locations
of our 4 intracluster MENeaCS SNe Ia has shown that
one is hosted by either a dwarf red sequence galaxy or
red GC (Abell 399); one is potentially associated with a
nearby spiral or irregular galaxy consistent with the red
sequence but also has a relatively high probability of be-
ing a chance alignment (Abell 2495); and two appear to
be truly hostless (Abell 1650 and Abell 85). We discuss
the implications of our results for the rates of SNe Ia in
faint cluster hosts in Section 4.1 and for the use of SNe Ia
as tracers of the ICL in Section 4.2.
11. 4.1. Implications for SN Ia Rates in Clusters
In Section 3 we found that the SN Ia in Abell 399 was
likely hosted by the faint object F, and that this source
is consistent with being either a cluster dwarf galaxy or
a GC. Here we consider the implications of both scenar-
ios on the rate of SNe Ia in dwarf galaxies and GCs, and
whether established SN Ia rates (or limits) in these pop-
ulations can constrain the physical nature of object F.
4.1.1. Dwarf Galaxies
If object F in Abell 399 is a dwarf galaxy, does this
imply a significantly enhanced SN Ia rate in faint cluster
galaxies? The rate per unit mass in a population, R,
is expressed by R = C × N/M, where C is a detection
efficiency, N is the number of SNe Ia, and M is the mass
in the population. As described in Sand et al. (2011),
our original CFHT deep stacks left 2% of the mass
in faint cluster galaxies undetected, but we now believe
that population has hosted 1 SN Ia. We can estimate the
implied relative rate per unit mass in the faintest 2% of
cluster galaxies with the following equation:
R2%
R
=
C2% × N2%/M2%
C × N/M
. (4)
Sand et al. (2011) describes how a small difference
in MENeaCS detection efficiencies between hosted and
hostless SNe Ia are introduced by two effects: (1) it is
more difficult to detect transients on top of a host galaxy
(even with difference imaging techniques), and (2) the
spectroscopic follow-up coverage for the hostless popu-
lation was slightly more extensive than for the hosted
SNe (they were run under separate proposals). Together,
this difference works out to be C2% = 1.2C. Sand et
al. (2012) present that the number of SNe Ia hosted by
all cluster galaxies within 1 Mpc is N = 11, and so
with N2% = 1 we find that R2%/R ≈ 5.5. Repeating
this calculation using only red sequence cluster galaxies
yields a similar rate enhancement because the number of
SNe Ia in red sequence members within 1 Mpc is NRS = 6
(i.e., 0.5N), the stellar mass in red sequence galaxies is
MRS ∼ 0.5M, and CRS = C.
Ultimately this potential rate enhancement by a fac-
tor of ∼ 5 is quite uncertain, as it is based on just one
SN Ia and an indirect estimate of the amount of mass in
faint cluster galaxies. As introduced in § 1.1 and 3.4,
by assuming the SN Ia rate per stellar mass is equal in
all cluster populations we estimated that the expectation
value for the number of MENeaCS SNe Ia in dwarf hosts
is ∼ 0.5. For a more restrictive estimate of the expecta-
tion value, we limit to red sequence galaxies within the
clustercentric radius of 1 Mpc used above. Assuming the
rate in bright cluster red sequence galaxies (∼ 50% of
the stellar mass hosting NRS = 6 SNe Ia) is the same as
that in dwarf red sequence galaxies (∼ 2% of the stellar
mass), the expectation value is ∼ 0.24 SNe Ia in dwarf
hosts. With Poisson statistics the probability of observ-
ing ≥ 1 SN Ia given this expectation value is 0.16, and
the 1σ uncertainties our estimated rate enhancement are
5.512.7
−4.5 (Gehrels 1986) – consistent with no rate enhance-
ment. Furthermore, if the luminosity function is steeper
than expected there could be more than 2% of the stellar
mass residing in such faint red galaxies. We plan to use
our deep HST images to constrain the faint-end slope of
the cluster luminosity function in later work, but con-
sider it beyond the scope of this paper.
The potential SN Ia rate enhancement by a factor of
∼ 5 in the faintest dwarf galaxies is not too large to be
unphysical, as the SN Ia rate is known to vary by factors
of that size (and more) with host galaxy properties such
as the specific star formation rate (e.g. Mannucci et al.
2005; Scannapieco & Bildsten 2005; Sullivan et al. 2006;
Smith et al. 2012). This potential rate enhancement is
also not so large that we expect to have already observed
it in wide-field sky surveys such as SDSS. For example,
Smith et al. (2012) find that the SN Ia rate per unit
mass decreases as a function of host stellar mass, but
their lowest stellar mass bin is ∼ 5 × 108
M⊙ and the
uncertainty on its rate is a factor of ∼ 2–3. Furthermore,
they mention that ∼ 2% of the SNe Ia in their sample
have undetected host galaxies. Current and future wide-
field surveys such as the Palomar Transient Factory and
the LSST should be able to improve the SN Ia rate in
faint dwarf galaxies (e.g., Conroy & Bullock 2015).
4.1.2. Globular Clusters
If object F in Abell 399 is a GC, it would be the first
confirmed GC to host a SN Ia. As GCs are purely old
stellar populations (> 2 Gyr), such an association would
also be direct confirmation that SNe Ia progenitors in-
clude truly old star systems. The fraction of galaxy stel-
lar mass in GC systems is ∼ 2×10−3
for elliptical galax-
ies (Harris et al. 2009; Peng et al. 2008; Zaritsky et
al. 2015). Based on this and the total stellar mass in
red sequence galaxies in MENeaCS clusters, we estimate
that 1012
M⊙ in GCs has been surveyed by MENeaCS.
If object F is a GC and has produced a SN Ia, it implies
a rate ∼25 times higher than the rate in our cluster red
sequence galaxies from Sand et al. (2012). This is on
a similar scale to theoretically predicted enhancements
due to dynamical interactions in the dense stellar en-
vironments of GCs (Pfahl et al. 2009), and below the
current limits placed by non-detections of GC at the lo-
cations of SNe Ia in archival HST images ( 42×; Voss
& Nelemans 2012; Washabaugh & Bregman 2013).
Would such an enhanced rate in GCs have already been
noticed? Potentially not. It would imply that 5% of
the SNe Ia in ellipticals are hosted by their GCs, but
as we discussed in Section 3.3.3 the radial distribution
of GCs follows the galaxy light profile and drops off at
∼ 5R. It is entirely conceivable that GC-hosted SNe have
simply been assigned as belonging to the parent galaxy.
This might lead to a relative rate enhancement in the
outer regions of ellipticals, which could be measured and
attributed to GCs. However, such an effect would be
difficult to confidently measure for two reasons. First,
there is a detection bias of SNe being easier to find when
they are not embedded deep in the host galaxy. Second,
a stellar population originating in GCs – able to produce
an enhanced rate of SN Ia – may have previously released
into the halos (or bulges) of galaxies from GCs due to col-
lisions with clouds or other GCs, winds from supernovae
in the GC, tidal forces for GC on elliptical orbits about
their host, evaporation of stars during interal GC relax-
ation, and/or dynamical friction (Fall & Rees, 1985). It
is conceivable that these issues combined could conspire
to blur the signal of a SN Ia rate enhancement in GCs in
the radial distribution of SNe Ia.
12. 4.1.3. Rates Summary
We find that the implied SN Ia rate enhancements in
either dwarf galaxies or GCs do not conflict with exist-
ing observations or theoretical predictions, but also do
not provide a means to constrain the nature of object F.
Additionally, if either of the 2 SNe Ia in Abell 1650 and
Abell 85 – which appear hostless in our deep HST images
– were in fact hosted by the ∼ 0.2% of the stellar mass
in small galaxies that remains below our limiting magni-
tudes, then by Equation 4 this indicates a rate enhance-
ment by a factor of ∼ 55 in the faintest dwarf galaxies.
This is conspicuously high and would have been noticed
in wide-field surveys. We therefore conclude that these 2
SNe Ia were truly hosted by the population of intraclus-
ter stars stripped from their host galaxy and residing in
the cluster’s gravitational potential.
4.2. Implications for IC SNe Ia as Tracers of the ICL
Sand et al. (2011) reported that of the 23 cluster
SNe Ia discovered by MENeaCS, 4 had no apparent host
galaxy in deep CFHT images that left just ∼ 2% of the
total cluster stellar mass in undetected faint galaxies.
With our deep HST imaging we find that 1 out of the
23 cluster SNe Ia, ∼ 4%, is hosted by a faint point-source
(object F in Abell 399). Finding ∼ 4% of the SNe Ia
hosted by ∼ 2% of the stellar mass is not surprising, but
here we take a closer look at how fICL is derived in order
to confirm the utility of SNe Ia as tracers of the ICL at
higher redshift.
The fraction of intracluster light, fICL, is calculated
by dividing the number of hostless SNe Ia by the total
number of cluster SNe Ia (hosted+hostless) discovered
by MENeaCS (Sand et al. 2011). To do this, the de-
tection efficiencies must be equal for hosted and hostless
SNe Ia; in other words, a survey must apply the same
discovery and spectroscopic classification constraints to
both populations, or be able to account for any bias in
the pipeline. This was true for all MENeaCS SNe Ia ex-
cept the IC SN in Abell 2495, which was preferentially
observed with Gemini spectroscopy despite being fainter
than the magnitude limit applied to follow-up of ME-
NeaCS SNe. For this reason, the hostless SN in Abell
2495 was not included in the calculation of the fraction
of IC stellar mass in Sand et al. (2011). In order to
combine only the same physical regions of each cluster,
they limit to a radius < R200 (i.e., the virial radius); all
four apparently hostless SNe Ia are within R200. Using
the remaining 3 apparently hostless SNe Ia as intraclus-
ter, and the 13 hosted SNe Ia within R200, Sand et al.
(2011) measure fICL = 0.16+0.13
−0.09.
Given the proximity of the SN Ia in Abell 399 to a
large nearby galaxy (see Section 3.3.3), they also repeat
this calculation assuming that this SN Ia was hosted, and
find fICL = 0.11+0.12
−0.07. In light of the faint object F at
the location of the SN Ia in Abell 399, we can now say
the latter is the more accurate measurement of fICL. Al-
though this distinction may not seem significant because
the difference between these two fICL measurements is
within their relatively large statistical errors, future facil-
ities such as the Large Synoptic Survey Telescope (LSST)
will generate bigger sample sizes and have smaller un-
certainties and a better understanding of the fraction of
apparently hostless SNe Ia will be needed in this regime.
LSST itself will be able to provide this because its deep
stack images have a projected detection limit of r ∼ 27.5
mag5
.
Until then, we can only caution that future surveys
will have to consider that 25–30% of apparently hostless
SNe Ia might not belong to the IC stellar population. Is
that too large for hostless SNe Ia to be scientifically use-
ful tracers of fICL at higher redshifts? Some numerical
simulations indicate that fICL grows with cosmological
time, and by z ∼ 0 is ∼ 2× larger than at z ∼ 0.4 (e.g.
Murante et al. 2007); others find that most IC stars
are stripped at z > 1, in which case fICL would remain
constant since then (Puchwein et al. 2010). Direct mea-
surements of this low surface brightness component have
shown that fICL 25% at z 0.1 and ∼ 10% at z ∼ 0.2
(e.g. Gonzalez et al. 2007; Zibetti et al. 2005), but HST
imaging of 0.4 < z < 0.8 clusters has found no evolution
in fICL since z < 0.8 (Guennou et al. 2012). We there-
fore surmise that assessments of fICL from SNe Ia will
require uncertainties of < 30% in order to compare with
some theoretical models and the direct surface bright-
ness measurements. This sounds discouraging, but there
is hope: below, we suggest that the best way to improve
this uncertainty and use hostless SNe Ia as high-redshift
ICL tracers is to constrain the SN Ia occurrence rate in
faint hosts.
Dwarf galaxies represent a small fraction of the total
cluster stellar mass, which is constrained by measure-
ments of the galaxy luminosity function. If their SN Ia
occurrence rate is equal to that in elliptical galaxies, then
measurements of fICL can account for the contamination
from apparently hostless SNe Ia in dwarf hosts. However,
in the preceding section we show that if object F is a clus-
ter dwarf, the SN Ia occurrence rate in the faintest ∼ 2%
of cluster galaxies could be up to ∼ 5× higher than in
elliptical galaxies. If confirmed, the number of SNe Ia in
faint dwarfs could be up to half of all apparently hostless
SNe Ia.
Compared to dwarf galaxies, GC represent an even
smaller fraction ( 0.002) of the total stellar mass in
clusters – much less than the fraction of intracluster stars
(∼ 0.16). If their SN Ia occurrence rate is equal to that
in elliptical galaxies, accidentally including the very few
SNe Ia in GC at large radial offsets from their host as part
of the ICL will have a negligible effect on measurements
of fICL. (Most SNe Ia in GC will be associated with el-
liptical galaxies, because GC have a radial distribution
similar to that of stars.) On the other hand, if the SN Ia
occurrence rate in GC is 25× that in elliptical galaxies
– as implied if object F is a GC – then up to ∼ 5% of
all cluster SNe Ia, and up to ∼ 30% of the apparently
hostless cluster SNe Ia, may actually be associated with
GCs.
In this work we have shown that ∼ 75% of all ap-
parently hostless SNe Ia are truly intracluster, and that
contamination is only a significant problem if the SN Ia
occurrence rate in low-mass galaxies or GC is enhanced.
This issue can be resolved by SN Ia rates analyses from
low-redshift, wide-field surveys such as the Palomar
Transient Factory, SDSS, or LSST, combined with deep
imaging for a larger sample of low-redshift apparently
hostless SN Ia. Such an effort should sufficiently con-
5 http://lsst.org/lsst/science/science portfolio
13. strain the SN Ia rate in dwarfs and GCs such that ex-
tremely deep imaging will not be required to confirm all
apparently hostless cluster SNe Ia, and facilitate their use
as tracers of the ICL to higher redshifts.
5. CONCLUSION
We have presented deep HST+ACS images at the lo-
cations of 4 IC SNe Ia in rich galaxy clusters, obtained
>3 years after explosion. This is the largest single-survey
sample of IC SNe Ia in rich clusters, and these data are
the deepest images ever obtained at the locations of IC
SNe Ia, lowering the amount of stellar mass left unde-
tected in cluster galaxies from ∼ 2% to just ∼ 0.2%
( 0.005% if we assume a shallow faint-end slope for
the galaxy luminosity function, αd = −1.0). We have
confirmed that the 2 SNe Ia in Abell 1650 and Abell 85
are hostless, and truly belong to the intracluster stellar
population of stars stripped from their host galaxy and
residing in the cluster potential. This indicates that at
least some SN Ia progenitors have truly old progenitor
stars (> 2 Gyr). We could not rule out that the SN Ia in
Abell 2495 was hosted by a nearby disk galaxy that has a
magnitude, color, and size consistent with cluster mem-
bership, but also found a relatively high probability that
this is a random association. We have shown that the
SN Ia in Abell 399 was very likely hosted by a faint red
point-like source that has a magnitude and color consis-
tent with both dwarf red sequence galaxies and red GCs.
Our statistical analysis of the expected surface densities
has shown that a dwarf galaxy is less likely at that loca-
tion than a GC, due to the presence of a nearby elliptical
galaxy. We have demonstrated that the rate enhance-
ments in dwarfs or GCs implied by this new faint host are
plausible under current observational constraints, and we
do not reject either hypothesis. We have also explicitly
ruled out the possibility that we could observe extremely
late-time emission from the SNe Ia themselves or a pos-
sible shocked companion.
Our discovery of a faint host galaxy for 1 of the 4
SNe Ia that appeared to be hostless is a potential prob-
lem for measuring the evolution in the fraction of intra-
cluster light across cosmic time, because fICL will need to
have uncertainties < 25% in order to distinguish between
models or compare with independent measurements. For
this reason we argue that hostless SNe Ia in rich clusters
should be used to measure fICL with caution, and that
it would be best if deep imaging for a larger sample of
low-redshift, apparently hostless SNe Ia were obtained in
order to better constrain the rate in dwarf galaxies and
GCs.
This work is based on observations made with the
NASA/ESA Hubble Space Telescope and obtained from
the Mikulski Archive for Space Telescopes at the Space
Telescope Science Institute, which is operated by the
Association of Universities for Research in Astronomy,
Inc., under NASA contract NAS 5-26555. These observa-
tions are associated with program #12937 and partially
funded by a NASA grant. We thank the HST staff for
their assistance with this program.
This work is also based in part on observations ob-
tained with MegaPrime/MegaCam, a joint project of
CFHT and CEA/DAPNIA, at the CanadaFranceHawaii
Telescope (CFHT) which is operated by the National Re-
search Council (NRC) of Canada, the Institut National
des Science de lUnivers of the Centre National de la
Recherche Scientifique (CNRS) of France, and the Uni-
versity of Hawaii. We remain grateful to the operators of
the CFHT queue without whom the original MENeaCS
project would not have been possible.
MLG’s position in the supernova research group at
U.C. Berkeley is supported by Gary & Cynthia Bengier.
MLG and DJS were supported during HST proposal
preparation by the Las Cumbres Observatory Global
Telescope Network. CJP is supported by the Natural
Sciences and Engineering Research Council of Canada.
We thank our anonymous reviewer for their constructive
comments and useful suggestions.
REFERENCES
Agulli, I., Aguerri, J. A. L., S´anchez-Janssen, R., Barrena, R.,
Diaferio, A., Serra, A. L. and M´endez-Abreu, J. 2014, MNRAS,
444, 34
Bell, E. F., McIntosh, D. H., Katz, N. and Weinberg, M. D. 2003,
ApJS, 149, 289
Bertin, E. and Arnouts, S. 1996, A&AS, 117, 393
Blanton, M. R. et al. 2003, ApJ, 592, 819
Blanton, M. R. and Roweis, S. 2007, AJ, 133, 734
Blondin, S. and Tonry, J. L. 2007, ApJ, 666, 1024
Brodie, J. P. and Strader, J. 2006, ARA&A, 44, 193
Boulade et al. 2003, in Society of Photo-Optical Instrumentation
Engineers (SPIE) Conference Series, Vol. 4841, Society of
Photo-Optical Instrumentation Engineers (SPIE) Conference
Series, ed. M. Iye & A. F. M. Moorwood, 72–81
Cappellaro, E., Mazzali, P. A., Benetti, S., Danziger, I. J.,
Turatto, M., della Valle, M. and Patat, F. 1997, A&A, 328, 203
Conroy, C. and Bullock, J. S. 2015, ApJL, [arXiv:1504.04015]
DeMaio, T., Gonzalez, A. H., Zabludoff, A., Zaritsky, D. and
Bradaˇc, M. 2015, MNRAS, 448, 1162
Durrell, P. R. and Ciardullo, R. and Feldmeier, J. J. and Jacoby,
G. H. and Sigurdsson, S. 2002, ApJ, 570, 119
Eisenstein, D. J., Annis, J., Gunn, J. E., Szalay, A. S., Connolly,
A. J. et al. 2001, AJ, 122, 2267
Fall, S. M. and Rees, M. J. 1985, ApJ, 298, 18
Feldmeier, J. J., Ciardullo, R., Jacoby, G. H. and Durrell, P. R.
2004, ApJ, 615, 196
Gal-Yam, A., Maoz, D., Guhathakurta, P. and Filippenko, A. V.
2003, AJ, 125, 1087
Gehrels, N. 1986, ApJ, 303, 336
Girardi, L., Groenewegen, M. A. T., Hatziminaoglou, E. and da
Costa, L. 2005, A&A, 436, 895
Gonzaga, S., Hack, W., Fruchter, A., Mack, J., eds. 2012, The
DrizzlePac Handbook. (Baltimore, STScI)
Gonzalez, A. H., Zabludoff, A. I. and Zaritsky, D. 2005, ApJ, 618,
195
Gonzalez, A. H., Zaritsky, D. and Zabludoff, A. I. 2007, ApJ, 666,
147
Graham, M. L. et al. 2012, ApJ, 753, 68
Graham, M. L. et al. 2015, MNRAS, 446, 2073
Graham, M. L., Nugent, P. E., Sullivan, M., Filippenko, A. V.,
Cenko, S. B., Silverman, J. M., Clubb, K. I. and Zheng, W.
2015, MNRAS, [arXiv:1502.00646]
Guennou, L. et al. 2012, A&A, 537, 64
Harris, W. E., Kavelaars, J. J., Hanes, D. A., Pritchet, C. J. and
Baum, W. A. AJ, 137, 3314
Holland, F. C. et al. 1998, SPIE, 3356, 234
Howell, D. A., Sullivan, M., Brown, E. F., Conley, A., Le Borgne,
D. et al. 2009, ApJ, 691, 661
Howell, D. A. 2011, Nature Communications, 2, 350.
Ivanova, N., Heinke, C. O., Rasio, F. A., Taam, R. E., Belczynski,
K. and Fregeau, J. 2006, MNRAS, 372, 1043
14. Kerzendorf, W. E., Taubenberger, S., Seitenzahl, and I. R.,
Ruiter, A. J., 2014, ApJ, 796, 26
Kinney, A. L., Calzetti, D., Bohlin, R. C., McQuade, K.,
Storchi-Bergmann, T., Schmitt, H. R. 1996, ApJ, 467, 38
Khochfar, S., Silk, J., Windhorst, R. A., and Ryan, R. E., Jr.
2007, ApJ, 668, 115
Krist, J. E., Hook, R. N. and Stoehr, F. 2011, SPIE Conference
Series, 8127, 0
Lunnan, R., Chornock, R., Berger, E., Laskar, T., Fong, W., Rest,
A., Sanders, N. E., Challis, P. M., et al. 2014, ApJ, 787, 138.
Neill, J. D., Shara, M. M. and Oegerle, W. R. 2005, ApJ, 618, 692
Neill, J. D., Sullivan, M., Gal-Yam, A., Quimby, R., Ofek, E.,
Wyder, T. K., Howell, D. A., Nugent, P. et al. 2011, ApJ, 727,
15
Maoz, D., Mannucci, F., and Nelemans, G. 2014, ARA&A, 52, 107
Mannucci, F., Della Valle, M., Panagia, N., Cappellaro, E.,
Cresci, G., Maiolino, R., Petrosian, A. and Turatto, M. 2005,
A&A, 433, 807
McGee, S. L., and Balogh, M. L. 2010, MNRAS, 403, L79
Milne, M. L., Pritchet, C. J., Poole, G. B., Gwyn, S. D. J.,
Kavelaars, J. J., Harris, W. E. and Hanes, D. A. 2007, AJ, 133,
177
Montes, M. and Trujillo, I. 2014, ApJ, 794, 137
Murante, G., Giovalli, M., Gerhard, O., Arnaboldi, M., Borgani,
S. and Dolag, K. 2007, MNRAS, 377, 2
Pan, K.-C., Ricker, P. M., Taam, R. E. 2013, ApJ, 773, 49
Peng et al. 2008, ApJ, 681, 197
Peng E. et al. 2011, ApJ, 730, 23
Pfahl, E., Scannapieco, E. and Bildsten, L. 2009, ApJ, 695, 111
Prescott, M. et al. MNRAS, 417, 1374
Puchwein, E., Springel, V., Sijacki, D. and Dolag, K. 2010,
MNRAS, 406, 936
Purcell, C. W., Bullock, J. S. and Zentner, A. R. 2007, ApJ, 666,
20
Quimby, R. M., Yuan, F., Akerlof, C., Wheeler, J. C., Warren,
M. S. 2012, AJ, 144, 177
Sand, D. J. et al. 2011, ApJ, 729, 142
Sand, D. J. et al. 2012, ApJ, 746, 163
Scannapieco, E. and Bildsten, L. 2005, ApJ, 629, 85
Schlafly E. F., Finkbeiner D. P., 2011, ApJ, 737, 103
Schlegel D. J., Finkbeiner D. P. and Davis M., 1998, ApJ, 500,
525
Seitenzahl, I. R., Taubenberger, S. and Sim, S. A. 2009, MNRAS,
400, 531
Shara, M. M. and Hurley, J. R. 2006, ApJ, 646, 464
Sirianni, M. et al., PASP, 117, 1049
Shappee, B. J., Kochanek, C. S., Stanek, K Z. 2013, ApJ, 765, 150
Smith, M. et al. 2012, ApJ, 755, 61
Sollerman, J. (et al. 2004, A&A, 428, 555
Sommer-Larsen, J., Romeo, A. D. and Portinari, L. 2005,
MNRAS, 357, 478
Suh, H., Yoon, S.-c., Jeong, H. and Yi, S. K. 2011, ApJ, 730, 110
Sullivan, M. et al. 2006, ApJ, 648, 868
Taubenberger, S. et al. 2015, MNRAS, 448, 48
Trentham, N. and Tully, R. B. 2002, MNRAS, 335, 3
Turatto, M., Benetti, S., Cappellaro, E., Danziger, I. J., Della
Valle, M., Gouiffes, C., Mazzali, P. A. and Patat, F. 1996,
MNRAS, 283, 1
Voss, R. and Nelemans, G. 2012, A&A, 539, 77
Washabaugh, P. C. and Bregman, J. N. 2013, ApJ, 762, 1
West, M. J., Jord´an, A., Blakeslee, J. P., Cˆot´e, P., Gregg, M. D.,
Takamiya, M. and Marzke, R. O. 2011, A&A, 528, 115
Williams, R. E. et al. 1996, AJ, 112, 1335
Yamanoi, H. et al. 2007, AJ, 134, 56
Zaritsky, D. et al. 2015, ApJ, 799, 159
Zibetti, S., White, S. D. M., Schneider, D. P. and Brinkmann, J.
2005, MNRAS, 358, 949