This document presents a sample of 151 dwarf galaxies that exhibit optical spectroscopic signatures of accreting massive black holes. The sample was identified by systematically searching ~25,000 emission-line galaxies from the Sloan Digital Sky Survey with stellar masses comparable to or less than the Large Magellanic Cloud. Many of the galaxies show narrow-line signatures of black hole accretion, and some also exhibit broad H-alpha emission, indicating gas orbiting in the deep potential of a massive black hole. This increases the number of known active galaxies in this low stellar mass range by over an order of magnitude. The median stellar mass of the host galaxies is around 108.5 solar masses, around 1-2 magnitudes fainter than previous samples of
Beyond the Kuiper Belt Edge: New High Perihelion Trans-Neptunian Objects With...Sérgio Sacani
We are conducting a survey for distant solar system objects beyond the Kuiper
Belt edge ( 50 AU) with new wide-field cameras on the Subaru and CTIO tele-
scopes. We are interested in the orbits of objects that are decoupled from the
giant planet region in order to understand the structure of the outer solar sys-
tem, including whether a massive planet exists beyond a few hundred AU as first
reported in Trujillo and Sheppard (2014). In addition to discovering extreme
trans-Neptunian objects detailed elsewhere, we have found several objects with
high perihelia (q > 40 AU) that differ from the extreme and inner Oort cloud
objects due to their moderate semi-major axes (50 < a < 100 AU) and eccen-
tricities (e . 0.3). Newly discovered objects 2014 FZ71 and 2015 FJ345 have
the third and fourth highest perihelia known after Sedna and 2012 VP113, yet
their orbits are not nearly as eccentric or distant. We found several of these high
perihelion but moderate orbit objects and observe that they are mostly near Nep-
tune mean motion resonances and have significant inclinations (i > 20 degrees).
These moderate objects likely obtained their unusual orbits through combined
interactions with Neptune’s mean motion resonances and the Kozai resonance,
similar to the origin scenarios for 2004 XR190. We also find the distant 2008
ST291 has likely been modified by the MMR+KR mechanism through the 6:1
Neptune resonance. We discuss these moderately eccentric, distant objects along
with some other interesting low inclination outer classical belt objects like 2012
FH84 discovered in our ongoing survey.
Beyond the Kuiper Belt Edge: New High Perihelion Trans-Neptunian Objects With...Sérgio Sacani
We are conducting a survey for distant solar system objects beyond the Kuiper
Belt edge ( 50 AU) with new wide-field cameras on the Subaru and CTIO tele-
scopes. We are interested in the orbits of objects that are decoupled from the
giant planet region in order to understand the structure of the outer solar sys-
tem, including whether a massive planet exists beyond a few hundred AU as first
reported in Trujillo and Sheppard (2014). In addition to discovering extreme
trans-Neptunian objects detailed elsewhere, we have found several objects with
high perihelia (q > 40 AU) that differ from the extreme and inner Oort cloud
objects due to their moderate semi-major axes (50 < a < 100 AU) and eccen-
tricities (e . 0.3). Newly discovered objects 2014 FZ71 and 2015 FJ345 have
the third and fourth highest perihelia known after Sedna and 2012 VP113, yet
their orbits are not nearly as eccentric or distant. We found several of these high
perihelion but moderate orbit objects and observe that they are mostly near Nep-
tune mean motion resonances and have significant inclinations (i > 20 degrees).
These moderate objects likely obtained their unusual orbits through combined
interactions with Neptune’s mean motion resonances and the Kozai resonance,
similar to the origin scenarios for 2004 XR190. We also find the distant 2008
ST291 has likely been modified by the MMR+KR mechanism through the 6:1
Neptune resonance. We discuss these moderately eccentric, distant objects along
with some other interesting low inclination outer classical belt objects like 2012
FH84 discovered in our ongoing survey.
DISCOVERY OF A GALAXY CLUSTER WITH A VIOLENTLY STARBURSTING CORE AT z = 2:506Sérgio Sacani
We report the discovery of a remarkable concentration of massive galaxies with extended X-ray
emission at zspec = 2:506, which contains 11 massive (M & 1011M) galaxies in the central 80kpc
region (11.6 overdensity). We have spectroscopically conrmed 17 member galaxies with 11 from CO
and the remaining ones from H. The X-ray luminosity, stellar mass content and velocity dispersion
all point to a collapsed, cluster-sized dark matter halo with mass M200c = 1013:90:2M, making it
the most distant X-ray-detected cluster known to date. Unlike other clusters discovered so far, this
structure is dominated by star-forming galaxies (SFGs) in the core with only 2 out of the 11 massive
galaxies classied as quiescent. The star formation rate (SFR) in the 80kpc core reaches 3400 M
yr 1 with a gas depletion time of 200 Myr, suggesting that we caught this cluster in rapid build-up
of a dense core. The high SFR is driven by both a high abundance of SFGs and a higher starburst
fraction ( 25%, compared to 3%-5% in the eld). The presence of both a collapsed, cluster-sized
halo and a predominant population of massive SFGs suggests that this structure could represent an
important transition phase between protoclusters and mature clusters. It provides evidence that the
main phase of massive galaxy passivization will take place after galaxies accrete onto the cluster,
providing new insights into massive cluster formation at early epochs. The large integrated stellar
mass at such high redshift challenges our understanding of massive cluster formation.
We report the discovery of a new Kepler transiting circumbinary planet (CBP).
This latest addition to the still-small family of CBPs defies the current trend of known
short-period planets orbiting near the stability limit of binary stars. Unlike the previous
discoveries, the planet revolving around the eclipsing binary system Kepler-1647 has
a very long orbital period ( 1100 days) and was at conjunction only twice during
the Kepler mission lifetime. Due to the singular configuration of the system, Kepler-
1647b is not only the longest-period transiting CBP at the time of writing, but also one
of the longest-period transiting planets. With a radius of 1:060:01 RJup it is also the
largest CBP to date. The planet produced three transits in the light-curve of Kepler-
1647 (one of them during an eclipse, creating a syzygy) and measurably perturbed the
times of the stellar eclipses, allowing us to measure its mass to be 1:520:65 MJup.
The planet revolves around an 11-day period eclipsing binary consisting of two Solarmass
stars on a slightly inclined, mildly eccentric (ebin = 0:16), spin-synchronized
orbit. Despite having an orbital period three times longer than Earth’s, Kepler-1647b is
in the conservative habitable zone of the binary star throughout its orbit.
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
We report the discovery of an optical Einstein Ring in the Sculptor constellation,
IAC J010127-334319, in the vicinity of the Sculptor Dwarf Spheroidal Galaxy. It is
an almost complete ring ( 300◦) with a diameter of 4.5 arcsec. The discovery was
made serendipitously from inspecting Dark Energy Camera (DECam) archive imaging
data. Confirmation of the object nature has been obtained by deriving spectroscopic
redshifts for both components, lens and source, from observations at the 10.4 m Gran
Telescopio CANARIAS (GTC) with the spectrograph OSIRIS. The lens, a massive
early-type galaxy, has a redshift of z = 0.581 while the source is a starburst galaxy
with redshift of z = 1.165. The total enclosed mass that produces the lensing effect
has been estimated to be Mtot = (1.86 ± 0.23) · 1012M⊙.
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.
SPECTROSCOPIC CONFIRMATION OF THE EXISTENCE OF LARGE, DIFFUSE GALAXIES IN THE...Sérgio Sacani
We recently identified a population of low surface brightness objects in the field of the z = 0.023 Coma cluster,
using the Dragonfly Telephoto Array. Here we present Keck spectroscopy of one of the largest of these “ultradiffuse
galaxies” (UDGs), confirming that it is a member of the cluster. The galaxy has prominent absorption
features, including the Ca II H+K lines and the G-band, and no detected emission lines. Its radial velocity of
cz=6280±120 km s−1 is within the 1σ velocity dispersion of the Coma cluster. The galaxy has an effective
radius of 4.3 ± 0.3 kpc and a Sérsic index of 0.89 ± 0.06, as measured from Keck imaging. We find no indications
of tidal tails or other distortions, at least out to a radius of ∼2re. We show that UDGs are located in a previously
sparsely populated region of the size—magnitude plane of quiescent stellar systems, as they are ∼6 mag fainter
than normal early-type galaxies of the same size. It appears that the luminosity distribution of large quiescent
galaxies is not continuous, although this could largely be due to selection effects. Dynamical measurements are
needed to determine whether the dark matter halos of UDGs are similar to those of galaxies with the same
luminosity or to those of galaxies with the same size.
Detection of solar_like_oscillations_in_relies_of_the_milk_way_asteroseismolo...Sérgio Sacani
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens
of thousands of field stars. Tests against independent estimates of these properties are however
scarce, especially in the metal-poor regime. Here, we report the detection of solar-like
oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular
cluster M4. The detections were made in photometric observations from the K2 Mission
during its Campaign 2. Making use of independent constraints on the distance, we estimate
masses of the 8 stars by utilising different combinations of seismic and non-seismic inputs.
When introducing a correction to the Δν scaling relation as suggested by stellar models, for
RGB stars we find excellent agreement with the expected masses from isochrone fitting, and
with a distance modulus derived using independent methods. The offset with respect to independent
masses is lower, or comparable with, the uncertainties on the average RGB mass
(4 − 10%, depending on the combination of constraints used). Our results lend confidence to
asteroseismic masses in the metal poor regime. We note that a larger sample will be needed
to allow more stringent tests to be made of systematic uncertainties in all the observables
(both seismic and non-seismic), and to explore the properties of RHB stars, and of different
populations in the cluster.
First identification of_direct_collapse_black_holes_candidates_in_the_early_u...Sérgio Sacani
The first black hole seeds, formed when the Universe was younger than ⇠ 500Myr, are recognized
to play an important role for the growth of early (z ⇠ 7) super-massive black holes.
While progresses have been made in understanding their formation and growth, their observational
signatures remain largely unexplored. As a result, no detection of such sources has been
confirmed so far. Supported by numerical simulations, we present a novel photometric method
to identify black hole seed candidates in deep multi-wavelength surveys.We predict that these
highly-obscured sources are characterized by a steep spectrum in the infrared (1.6−4.5μm),
i.e. by very red colors. The method selects the only 2 objects with a robust X-ray detection
found in the CANDELS/GOODS-S survey with a photometric redshift z & 6. Fitting their
infrared spectra only with a stellar component would require unrealistic star formation rates
(& 2000M# yr−1). To date, the selected objects represent the most promising black hole seed
candidates, possibly formed via the direct collapse black hole scenario, with predicted mass
> 105M#. While this result is based on the best photometric observations of high-z sources
available to date, additional progress is expected from spectroscopic and deeper X-ray data.
Upcoming observatories, like the JWST, will greatly expand the scope of this work.
Supermassive black holes in galaxy centres can grow by the accretion
of gas, liberating enormous amounts of energy that might
regulate star formation on galaxy-wide scales1–3
. The nature of
gaseous fuel reservoirs that power black hole growth is nevertheless
largely unconstrained by observations, and is instead routinely
simplified as a smooth, spherical inflow of very hot gas
in accordance with the Bondi solution4
. Recent theory5–7 and
simulations8–10 instead predict that accretion can be dominated by
a stochastic, clumpy distribution of very cold molecular clouds,
though unambiguous observational support for this prediction remains
elusive. Here we show observational evidence for a cold,
clumpy accretion flow toward a supermassive black hole fuel reservoir
in the nucleus of the Abell 2597 Brightest Cluster Galaxy
(BCG), a nearby (z = 0.0821) giant elliptical galaxy surrounded
by a dense halo of hot plasma11–13. Under the right conditions,
thermal instabilities can precipitate from this hot gas, producing a
rain of cold clouds that fall toward the galaxy’s centre14, sustaining
star formation amid a kiloparsec-scale molecular nebula that inhabits
its core15. New interferometric sub-millimetre observations
show that these cold clouds also fuel black hole accretion, revealing
“shadows” cast by molecular clouds as they move inward at ∼ 300
km s−1
toward the active supermassive black hole in the galaxy
centre, which serves as a bright backlight. Corroborating evidence
from prior observations16 of warmer atomic gas at extremely high
spatial resolution17, along with simple arguments based on geometry
and probability, indicates that these clouds are within the innermost
hundred parsecs of the black hole, and falling closer toward
it
Predictions of the_atmospheric_composition_of_gj_1132_bSérgio Sacani
GJ 1132 b is a nearby Earth-sized exoplanet transiting an M dwarf, and is amongst the most highly
characterizable small exoplanets currently known. In this paper we study the interaction of a magma
ocean with a water-rich atmosphere on GJ 1132b and determine that it must have begun with more
than 5 wt% initial water in order to still retain a water-based atmosphere. We also determine the
amount of O2
that can build up in the atmosphere as a result of hydrogen dissociation and loss.
We find that the magma ocean absorbs at most ∼ 10% of the O2 produced, whereas more than
90% is lost to space through hydrodynamic drag. The most common outcome for GJ 1132 b from our
simulations is a tenuous atmosphere dominated by O2
, although for very large initial water abundances
atmospheres with several thousands of bars of O2
are possible. A substantial steam envelope would
indicate either the existence of an earlier H2
envelope or low XUV flux over the system’s lifetime. A
steam atmosphere would also imply the continued existence of a magma ocean on GJ 1132 b. Further
modeling is needed to study the evolution of CO2
or N2
-rich atmospheres on GJ 1132 b.
Is there an_exoplanet_in_the_solar_systemSérgio Sacani
We investigate the prospects for the capture of the proposed Planet 9 from other
stars in the Sun’s birth cluster. Any capture scenario must satisfy three conditions:
the encounter must be more distant than ∼ 150 au to avoid perturbing the Kuiper
belt; the other star must have a wide-orbit planet (a & 100 au); the planet must be
captured onto an appropriate orbit to sculpt the orbital distribution of wide-orbit
Solar System bodies. Here we use N-body simulations to show that these criteria may
be simultaneously satisfied. In a few percent of slow close encounters in a cluster,
bodies are captured onto heliocentric, Planet 9-like orbits. During the ∼ 100 Myr
cluster phase, many stars are likely to host planets on highly-eccentric orbits with
apastron distances beyond 100 au if Neptune-sized planets are common and susceptible
to planet–planet scattering. While the existence of Planet 9 remains unproven, we
consider capture from one of the Sun’s young brethren a plausible route to explain such
an object’s orbit. Capture appears to predict a large population of Trans-Neptunian
Objects (TNOs) whose orbits are aligned with the captured planet, and we propose
that different formation mechanisms will be distinguishable based on their imprint on
the distribution of TNOs
A 2 4_determination_of_the_local_value_of_the_hubble_constantSérgio Sacani
We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to
reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%.
The bulk of this improvement comes from new, near-infrared observations of Cepheid
variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling
the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these
in turn leverage the magnitude-redshift relation based on 300 SNe Ia at z <0.15. All
19 hosts as well as the megamaser system NGC4258 have been observed with WFC3
in the optical and near-infrared, thus nullifying cross-instrument zeropoint errors in the
relative distance estimates from Cepheids. Other noteworthy improvements include a
33% reduction in the systematic uncertainty in the maser distance to NGC4258, a larger
sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to
the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of
Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW)
Cepheids.
Detection of lyman_alpha_emission_from_a_triply_imaged_z_6_85_galaxy_behind_m...Sérgio Sacani
We report the detection of Ly emission at 9538A
in the Keck/DEIMOS and HST WFC3
G102 grism data from a triply-imaged galaxy at z = 6:846 0:001 behind galaxy cluster MACS
J2129.4 0741. Combining the emission line wavelength with broadband photometry, line ratio upper
limits, and lens modeling, we rule out the scenario that this emission line is [O II] at z = 1:57. After
accounting for magnication, we calculate the weighted average of the intrinsic Ly luminosity to be
1:31042 erg s 1 and Ly equivalent width to be 7415A. Its intrinsic UV absolute magnitude at
1600A
is 18:60:2 mag and stellar mass (1:50:3)107 M, making it one of the faintest (intrinsic
LUV 0:14 L
UV) galaxies with Ly detection at z 7 to date. Its stellar mass is in the typical range
for the galaxies thought to dominate the reionization photon budget at z & 7; the inferred Ly escape
fraction is high (& 10%), which could be common for sub-L z & 7 galaxies with Ly emission. This
galaxy oers a glimpse of the galaxy population that is thought to drive reionization, and it shows
that gravitational lensing is an important avenue to probe the sub-L galaxy population.
The completeness-corrected rate of stellar encounters with the Sun from the f...Sérgio Sacani
I report on close encounters of stars to the Sun found in the first Gaia data release (GDR1). Combining Gaia astrometry with radial
velocities of around 320 000 stars drawn from various catalogues, I integrate orbits in a Galactic potential to identify those stars which
come within a few parsecs. Such encounters could influence the solar system, for example through gravitational perturbations of the
Oort cloud. 16 stars are found to come within 2 pc (although a few of these have dubious data). This is fewer than were found in a
similar study based on Hipparcos data, even though the present study has many more candidates. This is partly because I reject stars
with large radial velocity uncertainties (>10 km s−1
), and partly because of missing stars in GDR1 (especially at the bright end). The
closest encounter found is Gl 710, a K dwarf long-known to come close to the Sun in about 1.3 Myr. The Gaia astrometry predict
a much closer passage than pre-Gaia estimates, however: just 16 000 AU (90% confidence interval: 10 000–21 000 AU), which will
bring this star well within the Oort cloud. Using a simple model for the spatial, velocity, and luminosity distributions of stars, together
with an approximation of the observational selection function, I model the incompleteness of this Gaia-based search as a function
of the time and distance of closest approach. Applying this to a subset of the observed encounters (excluding duplicates and stars
with implausibly large velocities), I estimate the rate of stellar encounters within 5 pc averaged over the past and future 5 Myr to be
545±59 Myr−1
. Assuming a quadratic scaling of the rate within some encounter distance (which my model predicts), this corresponds
to 87 ± 9 Myr−1 within 2 pc. A more accurate analysis and assessment will be possible with future Gaia data releases.
TEMPORAL EVOLUTION OF THE HIGH-ENERGY IRRADIATION AND WATER CONTENT OF TRAPPI...Sérgio Sacani
The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could
harbour liquid water on their surfaces. UV observations are essential to measure their high-energy
irradiation, and to search for photodissociated water escaping from their putative atmospheres. Our
new observations of TRAPPIST-1 Ly-α line during the transit of TRAPPIST-1c show an evolution of
the star emission over three months, preventing us from assessing the presence of an extended hydrogen
exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history
of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the
orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape.
However, TRAPPIST-1e to h might have lost less than 3 Earth oceans if hydrodynamic escape stopped
once they entered the habitable zone. We caution that these estimates remain limited by the large
uncertainty on the planet masses. They likely represent upper limits on the actual water loss because
our assumptions maximize the XUV-driven escape, while photodissociation in the upper atmospheres
should be the limiting process. Late-stage outgassing could also have contributed significant amounts
of water for the outer, more massive planets after they entered the habitable zone. While our results
suggest that the outer planets are the best candidates to search for water with the JWST, they also
highlight the need for theoretical studies and complementary observations in all wavelength domains
to determine the nature of the TRAPPIST-1 planets, and their potential habitability.
Keywords: planetary systems - Stars: individual: TRAPPIST-1
On the possibility of through passage of asteroid bodies across the Earth’s a...Sérgio Sacani
We have studied the conditions of through passage of asteroids with diameters 200, 100, and
50 m, consisting of three types of materials – iron, stone, and water ice, across the Earth’s
atmosphere with a minimum trajectory altitude in the range 10–15 km. The conditions of this
passage with a subsequent exit into outer space with the preservation of a substantial fraction
of the initial mass have been found. The results obtained support our idea explaining one of the
long-standing problems of astronomy – the Tunguska phenomenon, which has not received
reasonable and comprehensive interpretations to date. We argue that the Tunguska event was
caused by an iron asteroid body, which passed through the Earth’s atmosphere and continued
to the near-solar orbit.
Extensive Noachian fluvial systems in Arabia Terra: Implications for early Ma...Sérgio Sacani
Valley networks are some of the strongest lines of evidence for
extensive fluvial activity on early (Noachian; >3.7 Ga) Mars. However,
their purported absence on certain ancient terrains, such as
Arabia Terra, is at variance with patterns of precipitation as predicted
by “warm and wet” climate models. This disagreement has contributed
to the development of an alternative “icy highlands” scenario,
whereby valley networks were formed by the melting of highland ice
sheets. Here, we show through regional mapping that Arabia Terra
shows evidence for extensive networks of sinuous ridges. We interpret
these ridge features as inverted fluvial channels that formed in
the Noachian, before being subject to burial and exhumation. The
inverted channels developed on extensive aggrading flood plains. As
the inverted channels are both sourced in, and traverse across, Arabia
Terra, their formation is inconsistent with discrete, localized sources
of water, such as meltwater from highland ice sheets. Our results are
instead more consistent with an early Mars that supported widespread
precipitation and runoff.
Exocometary gas in_th_hd_181327_debris_ringSérgio Sacani
An increasing number of observations have shown that gaseous debris discs are not an
exception. However, until now we only knew of cases around A stars. Here we present the first
detection of 12CO (2-1) disc emission around an F star, HD 181327, obtained with ALMA
observations at 1.3 mm. The continuum and CO emission are resolved into an axisymmetric
disc with ring-like morphology. Using a Markov chain Monte Carlo method coupled with
radiative transfer calculations we study the dust and CO mass distribution. We find the dust is
distributed in a ring with a radius of 86:0 0:4 AU and a radial width of 23:2 1:0 AU. At
this frequency the ring radius is smaller than in the optical, revealing grain size segregation
expected due to radiation pressure. We also report on the detection of low level continuum
emission beyond the main ring out to 200 AU. We model the CO emission in the non-LTE
regime and we find that the CO is co-located with the dust, with a total CO gas mass ranging
between 1:2 10 6 M and 2:9 10 6 M, depending on the gas kinetic temperature and
collisional partners densities. The CO densities and location suggest a secondary origin, i.e.
released from icy planetesimals in the ring. We derive a CO cometary composition that is
consistent with Solar system comets. Due to the low gas densities it is unlikely that the gas is
shaping the dust distribution.
The importance of comets for the origin of life on Earth has been advocated for many decades. Amino acids are
key ingredients in chemistry, leading to life as we know it. Many primitive meteorites contain amino acids, and it
is generally believed that these are formed by aqueous alterations. In the collector aerogel and foil samples of the
Stardust mission after the flyby at comet Wild 2, the simplest form of amino acids, glycine, has been found
together with precursor molecules methylamine and ethylamine. Because of contamination issues of the samples,
a cometary origin was deduced from the 13C isotopic signature. We report the presence of volatile glycine
accompanied by methylamine and ethylamine in the coma of 67P/Churyumov-Gerasimenko measured by
the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) mass spectrometer, confirming the
Stardust results. Together with the detection of phosphorus and a multitude of organic molecules, this result
demonstrates that comets could have played a crucial role in the emergence of life on Earth.
Proper-motion age dating of the progeny of Nova Scorpii ad 1437Sérgio Sacani
‘Cataclysmic variables’ are binary star systems in which one
star of the pair is a white dwarf, and which often generate bright
and energetic stellar outbursts. Classical novae are one type of
outburst: when the white dwarf accretes enough matter from its
companion, the resulting hydrogen-rich atmospheric envelope
can host a runaway thermonuclear reaction that generates a rapid
brightening1–4. Achieving peak luminosities of up to one million
times that of the Sun5
, all classical novae are recurrent, on timescales
of months6
to millennia7
. During the century before and after an
eruption, the ‘novalike’ binary systems that give rise to classical
novae exhibit high rates of mass transfer to their white dwarfs8
.
Another type of outburst is the dwarf nova: these occur in binaries
that have stellar masses and periods indistinguishable from those
of novalikes9
but much lower mass-transfer rates10, when accretiondisk
instabilities11 drop matter onto the white dwarfs. The coexistence
at the same orbital period of novalike binaries and dwarf
novae—which are identical but for their widely varying accretion
rates—has been a longstanding puzzle9
. Here we report the recovery
of the binary star underlying the classical nova eruption of 11 March
ad 1437 (refs 12, 13), and independently confirm its age by propermotion
dating. We show that, almost 500 years after a classical-nova
event, the system exhibited dwarf-nova eruptions. The three other
oldest recovered classical novae14–16 display nova shells, but lack
firm post-eruption ages17,18, and are also dwarf novae at present.
We conclude that many old novae become dwarf novae for part of
the millennia between successive nova eruptions19,
A 50000 solar_mass_black_hole_in_the_nucleous_of_rgg_118Sérgio Sacani
Astrônomos usando o Observatório de Raios-X Chandra da NASA e o Telescópio Clay de 6.5 metros no Chile, identificaram o menor buraco negro supermassivo já detectado no centro de uma galáxia. Esse objeto paradoxal poderia fornecer pistas sobre qual o tamanho de buracos negros formados juntos com suas galáxias hospedeiras a 13 bilhões de anos atrás, ou mais.
Os astrônomos estimam que esse buraco negro supermassivo tem cerca de 50000 vezes a massa do Sol. Isso é menos da metade do buraco negro anterior de menor massa encontrado no centro de uma galáxia.
O buraco negro está localizado no centro do disco da galáxia anã, chamada de RGG 118, localizada a cerca de 340 milhões de anos-luz de distância da Terra. A imagem principal desse post, foi feita pelo Sloan Digital Sky Survey e o detalhe mostra uma imagem feita pelo Chandra do centro da galáxia. A fonte pontual de raios-X, é produzida pelo gás quente que faz um movimento de redemoinho ao redor do buraco negro.
Os pesquisadores estimaram a massa do buraco negro estudando o movimento do gás frio perto do centro da galáxia, usando dados na luz visível obtidos pelo Telescópio Clay. Eles usaram os dados do Chandra para descobrir o brilho em raios-X do gás quente espiralando na direção do buraco negro. Eles encontraram que a força de empurrão da pressão da radiação desse gás quente é equivalente a cerca de 1% da força de puxão da gravidade interna, o que se ajusta bem com as propriedades de outros buracos negros supermassivos.
Anteriormente, uma relação tinha sido notada entre a massa dos buracos negros supermassivos e o intervalo de velocidades das estrelas no centro da galáxia hospedeira. Essa relação também é mantida para a RGG 118 e seu buraco negro.
O buraco negro na RGG 118 é cerca de 100 vezes menos massivo do que o buraco negro supermassivo encontrado no centro da Via Láctea. Ele é também cerca de 200000 vezes menos massivo do que o buraco negro mais massivo já encontrado no centro de outras galáxias.
Os astrônomos estão tentando entender a formação de buracos negros com bilhões de vezes a massa solar que têm sido detectados a menos de um bilhão de anos depois do Big Bang. O buraco negro na RGG 118 dá aos astrônomos uma oportunidade de estudar um buraco negro supermassivo, pequeno e próximo, pertencente à primeira geração de buracos negros que não são detectáveis pela nossa tecnologia atual.
Os astrônomos acreditam que buracos negros supermassivos podem se formar quando grandes nuvens de gás, com uma massa entre 10000 e 100000 vezes a massa do Sol, colapsa num buraco negro. Muitos desses buracos negros semeiam então fusões para formar buracos negros supermassivos ainda maiores. De maneira alternativa, um buraco negro supermassivo poderia surgir de uma estrela gigante, com cerca de 100 vezes a massa do Sol, que no final da sua vida, depois de consumir todo o seu combustível, colapsa e forma um buraco negro.
Os pesquisadore
A Chandra X-ray study of millisecond pulsars in the globular cluster Omega Ce...Sérgio Sacani
Millisecond pulsars (MSPs) are faint X-ray sources commonly observed in Galactic globular clusters (GCs). In this work, we
investigate 18 MSPs newly found in the GC Omega Centauri (𝜔 Cen) and search for their X-ray counterparts using Chandra
observations with a total exposure time of 290.9 ks. We identify confident X-ray counterparts for 11 of the MSPs, with 9 of
them newly identified in this work based on their positions, spectral properties, and X-ray colours. The X-ray spectra of 9 MSPs
are well described by a neutron star hydrogen atmosphere model, while 2 MSPs are well fitted by a power-law model. The
identified MSPs have X-ray luminosities ranging from 1.0 × 1030 erg s−1
to 1.4 × 1031 erg s−1
. Additionally, for population
comparison purposes, we study the X-ray counterpart to MSP E in the GC M71, and find its X-ray spectrum is well described
by blackbody-like models with a luminosity of 1.9 × 1030 erg s−1
. We investigate the empirical correlations between X-ray
luminosities and minimum companion masses, as well as mass functions, of spider pulsars. Clear correlations are observed, with
best-fit functions of log10 𝐿𝑋 = (1.0 ± 0.1) log10 𝑀𝑐,𝑚𝑖𝑛 + (32.5 ± 0.2) and log10 𝐿𝑋 = (0.35 ± 0.04) log10 MF + (32.71 ± 0.20),
respectively, with an intrinsic scatter of log10 𝐿𝑋 of ∼0.3, where 𝐿𝑋 is the 0.5–10 keV X-ray luminosity, 𝑀𝑐,𝑚𝑖𝑛 is the minimum
companion mass, and MF represents the mass function, in solar masses.
DISCOVERY OF A GALAXY CLUSTER WITH A VIOLENTLY STARBURSTING CORE AT z = 2:506Sérgio Sacani
We report the discovery of a remarkable concentration of massive galaxies with extended X-ray
emission at zspec = 2:506, which contains 11 massive (M & 1011M) galaxies in the central 80kpc
region (11.6 overdensity). We have spectroscopically conrmed 17 member galaxies with 11 from CO
and the remaining ones from H. The X-ray luminosity, stellar mass content and velocity dispersion
all point to a collapsed, cluster-sized dark matter halo with mass M200c = 1013:90:2M, making it
the most distant X-ray-detected cluster known to date. Unlike other clusters discovered so far, this
structure is dominated by star-forming galaxies (SFGs) in the core with only 2 out of the 11 massive
galaxies classied as quiescent. The star formation rate (SFR) in the 80kpc core reaches 3400 M
yr 1 with a gas depletion time of 200 Myr, suggesting that we caught this cluster in rapid build-up
of a dense core. The high SFR is driven by both a high abundance of SFGs and a higher starburst
fraction ( 25%, compared to 3%-5% in the eld). The presence of both a collapsed, cluster-sized
halo and a predominant population of massive SFGs suggests that this structure could represent an
important transition phase between protoclusters and mature clusters. It provides evidence that the
main phase of massive galaxy passivization will take place after galaxies accrete onto the cluster,
providing new insights into massive cluster formation at early epochs. The large integrated stellar
mass at such high redshift challenges our understanding of massive cluster formation.
We report the discovery of a new Kepler transiting circumbinary planet (CBP).
This latest addition to the still-small family of CBPs defies the current trend of known
short-period planets orbiting near the stability limit of binary stars. Unlike the previous
discoveries, the planet revolving around the eclipsing binary system Kepler-1647 has
a very long orbital period ( 1100 days) and was at conjunction only twice during
the Kepler mission lifetime. Due to the singular configuration of the system, Kepler-
1647b is not only the longest-period transiting CBP at the time of writing, but also one
of the longest-period transiting planets. With a radius of 1:060:01 RJup it is also the
largest CBP to date. The planet produced three transits in the light-curve of Kepler-
1647 (one of them during an eclipse, creating a syzygy) and measurably perturbed the
times of the stellar eclipses, allowing us to measure its mass to be 1:520:65 MJup.
The planet revolves around an 11-day period eclipsing binary consisting of two Solarmass
stars on a slightly inclined, mildly eccentric (ebin = 0:16), spin-synchronized
orbit. Despite having an orbital period three times longer than Earth’s, Kepler-1647b is
in the conservative habitable zone of the binary star throughout its orbit.
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
We report the discovery of an optical Einstein Ring in the Sculptor constellation,
IAC J010127-334319, in the vicinity of the Sculptor Dwarf Spheroidal Galaxy. It is
an almost complete ring ( 300◦) with a diameter of 4.5 arcsec. The discovery was
made serendipitously from inspecting Dark Energy Camera (DECam) archive imaging
data. Confirmation of the object nature has been obtained by deriving spectroscopic
redshifts for both components, lens and source, from observations at the 10.4 m Gran
Telescopio CANARIAS (GTC) with the spectrograph OSIRIS. The lens, a massive
early-type galaxy, has a redshift of z = 0.581 while the source is a starburst galaxy
with redshift of z = 1.165. The total enclosed mass that produces the lensing effect
has been estimated to be Mtot = (1.86 ± 0.23) · 1012M⊙.
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.
SPECTROSCOPIC CONFIRMATION OF THE EXISTENCE OF LARGE, DIFFUSE GALAXIES IN THE...Sérgio Sacani
We recently identified a population of low surface brightness objects in the field of the z = 0.023 Coma cluster,
using the Dragonfly Telephoto Array. Here we present Keck spectroscopy of one of the largest of these “ultradiffuse
galaxies” (UDGs), confirming that it is a member of the cluster. The galaxy has prominent absorption
features, including the Ca II H+K lines and the G-band, and no detected emission lines. Its radial velocity of
cz=6280±120 km s−1 is within the 1σ velocity dispersion of the Coma cluster. The galaxy has an effective
radius of 4.3 ± 0.3 kpc and a Sérsic index of 0.89 ± 0.06, as measured from Keck imaging. We find no indications
of tidal tails or other distortions, at least out to a radius of ∼2re. We show that UDGs are located in a previously
sparsely populated region of the size—magnitude plane of quiescent stellar systems, as they are ∼6 mag fainter
than normal early-type galaxies of the same size. It appears that the luminosity distribution of large quiescent
galaxies is not continuous, although this could largely be due to selection effects. Dynamical measurements are
needed to determine whether the dark matter halos of UDGs are similar to those of galaxies with the same
luminosity or to those of galaxies with the same size.
Detection of solar_like_oscillations_in_relies_of_the_milk_way_asteroseismolo...Sérgio Sacani
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens
of thousands of field stars. Tests against independent estimates of these properties are however
scarce, especially in the metal-poor regime. Here, we report the detection of solar-like
oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular
cluster M4. The detections were made in photometric observations from the K2 Mission
during its Campaign 2. Making use of independent constraints on the distance, we estimate
masses of the 8 stars by utilising different combinations of seismic and non-seismic inputs.
When introducing a correction to the Δν scaling relation as suggested by stellar models, for
RGB stars we find excellent agreement with the expected masses from isochrone fitting, and
with a distance modulus derived using independent methods. The offset with respect to independent
masses is lower, or comparable with, the uncertainties on the average RGB mass
(4 − 10%, depending on the combination of constraints used). Our results lend confidence to
asteroseismic masses in the metal poor regime. We note that a larger sample will be needed
to allow more stringent tests to be made of systematic uncertainties in all the observables
(both seismic and non-seismic), and to explore the properties of RHB stars, and of different
populations in the cluster.
First identification of_direct_collapse_black_holes_candidates_in_the_early_u...Sérgio Sacani
The first black hole seeds, formed when the Universe was younger than ⇠ 500Myr, are recognized
to play an important role for the growth of early (z ⇠ 7) super-massive black holes.
While progresses have been made in understanding their formation and growth, their observational
signatures remain largely unexplored. As a result, no detection of such sources has been
confirmed so far. Supported by numerical simulations, we present a novel photometric method
to identify black hole seed candidates in deep multi-wavelength surveys.We predict that these
highly-obscured sources are characterized by a steep spectrum in the infrared (1.6−4.5μm),
i.e. by very red colors. The method selects the only 2 objects with a robust X-ray detection
found in the CANDELS/GOODS-S survey with a photometric redshift z & 6. Fitting their
infrared spectra only with a stellar component would require unrealistic star formation rates
(& 2000M# yr−1). To date, the selected objects represent the most promising black hole seed
candidates, possibly formed via the direct collapse black hole scenario, with predicted mass
> 105M#. While this result is based on the best photometric observations of high-z sources
available to date, additional progress is expected from spectroscopic and deeper X-ray data.
Upcoming observatories, like the JWST, will greatly expand the scope of this work.
Supermassive black holes in galaxy centres can grow by the accretion
of gas, liberating enormous amounts of energy that might
regulate star formation on galaxy-wide scales1–3
. The nature of
gaseous fuel reservoirs that power black hole growth is nevertheless
largely unconstrained by observations, and is instead routinely
simplified as a smooth, spherical inflow of very hot gas
in accordance with the Bondi solution4
. Recent theory5–7 and
simulations8–10 instead predict that accretion can be dominated by
a stochastic, clumpy distribution of very cold molecular clouds,
though unambiguous observational support for this prediction remains
elusive. Here we show observational evidence for a cold,
clumpy accretion flow toward a supermassive black hole fuel reservoir
in the nucleus of the Abell 2597 Brightest Cluster Galaxy
(BCG), a nearby (z = 0.0821) giant elliptical galaxy surrounded
by a dense halo of hot plasma11–13. Under the right conditions,
thermal instabilities can precipitate from this hot gas, producing a
rain of cold clouds that fall toward the galaxy’s centre14, sustaining
star formation amid a kiloparsec-scale molecular nebula that inhabits
its core15. New interferometric sub-millimetre observations
show that these cold clouds also fuel black hole accretion, revealing
“shadows” cast by molecular clouds as they move inward at ∼ 300
km s−1
toward the active supermassive black hole in the galaxy
centre, which serves as a bright backlight. Corroborating evidence
from prior observations16 of warmer atomic gas at extremely high
spatial resolution17, along with simple arguments based on geometry
and probability, indicates that these clouds are within the innermost
hundred parsecs of the black hole, and falling closer toward
it
Predictions of the_atmospheric_composition_of_gj_1132_bSérgio Sacani
GJ 1132 b is a nearby Earth-sized exoplanet transiting an M dwarf, and is amongst the most highly
characterizable small exoplanets currently known. In this paper we study the interaction of a magma
ocean with a water-rich atmosphere on GJ 1132b and determine that it must have begun with more
than 5 wt% initial water in order to still retain a water-based atmosphere. We also determine the
amount of O2
that can build up in the atmosphere as a result of hydrogen dissociation and loss.
We find that the magma ocean absorbs at most ∼ 10% of the O2 produced, whereas more than
90% is lost to space through hydrodynamic drag. The most common outcome for GJ 1132 b from our
simulations is a tenuous atmosphere dominated by O2
, although for very large initial water abundances
atmospheres with several thousands of bars of O2
are possible. A substantial steam envelope would
indicate either the existence of an earlier H2
envelope or low XUV flux over the system’s lifetime. A
steam atmosphere would also imply the continued existence of a magma ocean on GJ 1132 b. Further
modeling is needed to study the evolution of CO2
or N2
-rich atmospheres on GJ 1132 b.
Is there an_exoplanet_in_the_solar_systemSérgio Sacani
We investigate the prospects for the capture of the proposed Planet 9 from other
stars in the Sun’s birth cluster. Any capture scenario must satisfy three conditions:
the encounter must be more distant than ∼ 150 au to avoid perturbing the Kuiper
belt; the other star must have a wide-orbit planet (a & 100 au); the planet must be
captured onto an appropriate orbit to sculpt the orbital distribution of wide-orbit
Solar System bodies. Here we use N-body simulations to show that these criteria may
be simultaneously satisfied. In a few percent of slow close encounters in a cluster,
bodies are captured onto heliocentric, Planet 9-like orbits. During the ∼ 100 Myr
cluster phase, many stars are likely to host planets on highly-eccentric orbits with
apastron distances beyond 100 au if Neptune-sized planets are common and susceptible
to planet–planet scattering. While the existence of Planet 9 remains unproven, we
consider capture from one of the Sun’s young brethren a plausible route to explain such
an object’s orbit. Capture appears to predict a large population of Trans-Neptunian
Objects (TNOs) whose orbits are aligned with the captured planet, and we propose
that different formation mechanisms will be distinguishable based on their imprint on
the distribution of TNOs
A 2 4_determination_of_the_local_value_of_the_hubble_constantSérgio Sacani
We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to
reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%.
The bulk of this improvement comes from new, near-infrared observations of Cepheid
variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling
the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these
in turn leverage the magnitude-redshift relation based on 300 SNe Ia at z <0.15. All
19 hosts as well as the megamaser system NGC4258 have been observed with WFC3
in the optical and near-infrared, thus nullifying cross-instrument zeropoint errors in the
relative distance estimates from Cepheids. Other noteworthy improvements include a
33% reduction in the systematic uncertainty in the maser distance to NGC4258, a larger
sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to
the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of
Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW)
Cepheids.
Detection of lyman_alpha_emission_from_a_triply_imaged_z_6_85_galaxy_behind_m...Sérgio Sacani
We report the detection of Ly emission at 9538A
in the Keck/DEIMOS and HST WFC3
G102 grism data from a triply-imaged galaxy at z = 6:846 0:001 behind galaxy cluster MACS
J2129.4 0741. Combining the emission line wavelength with broadband photometry, line ratio upper
limits, and lens modeling, we rule out the scenario that this emission line is [O II] at z = 1:57. After
accounting for magnication, we calculate the weighted average of the intrinsic Ly luminosity to be
1:31042 erg s 1 and Ly equivalent width to be 7415A. Its intrinsic UV absolute magnitude at
1600A
is 18:60:2 mag and stellar mass (1:50:3)107 M, making it one of the faintest (intrinsic
LUV 0:14 L
UV) galaxies with Ly detection at z 7 to date. Its stellar mass is in the typical range
for the galaxies thought to dominate the reionization photon budget at z & 7; the inferred Ly escape
fraction is high (& 10%), which could be common for sub-L z & 7 galaxies with Ly emission. This
galaxy oers a glimpse of the galaxy population that is thought to drive reionization, and it shows
that gravitational lensing is an important avenue to probe the sub-L galaxy population.
The completeness-corrected rate of stellar encounters with the Sun from the f...Sérgio Sacani
I report on close encounters of stars to the Sun found in the first Gaia data release (GDR1). Combining Gaia astrometry with radial
velocities of around 320 000 stars drawn from various catalogues, I integrate orbits in a Galactic potential to identify those stars which
come within a few parsecs. Such encounters could influence the solar system, for example through gravitational perturbations of the
Oort cloud. 16 stars are found to come within 2 pc (although a few of these have dubious data). This is fewer than were found in a
similar study based on Hipparcos data, even though the present study has many more candidates. This is partly because I reject stars
with large radial velocity uncertainties (>10 km s−1
), and partly because of missing stars in GDR1 (especially at the bright end). The
closest encounter found is Gl 710, a K dwarf long-known to come close to the Sun in about 1.3 Myr. The Gaia astrometry predict
a much closer passage than pre-Gaia estimates, however: just 16 000 AU (90% confidence interval: 10 000–21 000 AU), which will
bring this star well within the Oort cloud. Using a simple model for the spatial, velocity, and luminosity distributions of stars, together
with an approximation of the observational selection function, I model the incompleteness of this Gaia-based search as a function
of the time and distance of closest approach. Applying this to a subset of the observed encounters (excluding duplicates and stars
with implausibly large velocities), I estimate the rate of stellar encounters within 5 pc averaged over the past and future 5 Myr to be
545±59 Myr−1
. Assuming a quadratic scaling of the rate within some encounter distance (which my model predicts), this corresponds
to 87 ± 9 Myr−1 within 2 pc. A more accurate analysis and assessment will be possible with future Gaia data releases.
TEMPORAL EVOLUTION OF THE HIGH-ENERGY IRRADIATION AND WATER CONTENT OF TRAPPI...Sérgio Sacani
The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could
harbour liquid water on their surfaces. UV observations are essential to measure their high-energy
irradiation, and to search for photodissociated water escaping from their putative atmospheres. Our
new observations of TRAPPIST-1 Ly-α line during the transit of TRAPPIST-1c show an evolution of
the star emission over three months, preventing us from assessing the presence of an extended hydrogen
exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history
of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the
orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape.
However, TRAPPIST-1e to h might have lost less than 3 Earth oceans if hydrodynamic escape stopped
once they entered the habitable zone. We caution that these estimates remain limited by the large
uncertainty on the planet masses. They likely represent upper limits on the actual water loss because
our assumptions maximize the XUV-driven escape, while photodissociation in the upper atmospheres
should be the limiting process. Late-stage outgassing could also have contributed significant amounts
of water for the outer, more massive planets after they entered the habitable zone. While our results
suggest that the outer planets are the best candidates to search for water with the JWST, they also
highlight the need for theoretical studies and complementary observations in all wavelength domains
to determine the nature of the TRAPPIST-1 planets, and their potential habitability.
Keywords: planetary systems - Stars: individual: TRAPPIST-1
On the possibility of through passage of asteroid bodies across the Earth’s a...Sérgio Sacani
We have studied the conditions of through passage of asteroids with diameters 200, 100, and
50 m, consisting of three types of materials – iron, stone, and water ice, across the Earth’s
atmosphere with a minimum trajectory altitude in the range 10–15 km. The conditions of this
passage with a subsequent exit into outer space with the preservation of a substantial fraction
of the initial mass have been found. The results obtained support our idea explaining one of the
long-standing problems of astronomy – the Tunguska phenomenon, which has not received
reasonable and comprehensive interpretations to date. We argue that the Tunguska event was
caused by an iron asteroid body, which passed through the Earth’s atmosphere and continued
to the near-solar orbit.
Extensive Noachian fluvial systems in Arabia Terra: Implications for early Ma...Sérgio Sacani
Valley networks are some of the strongest lines of evidence for
extensive fluvial activity on early (Noachian; >3.7 Ga) Mars. However,
their purported absence on certain ancient terrains, such as
Arabia Terra, is at variance with patterns of precipitation as predicted
by “warm and wet” climate models. This disagreement has contributed
to the development of an alternative “icy highlands” scenario,
whereby valley networks were formed by the melting of highland ice
sheets. Here, we show through regional mapping that Arabia Terra
shows evidence for extensive networks of sinuous ridges. We interpret
these ridge features as inverted fluvial channels that formed in
the Noachian, before being subject to burial and exhumation. The
inverted channels developed on extensive aggrading flood plains. As
the inverted channels are both sourced in, and traverse across, Arabia
Terra, their formation is inconsistent with discrete, localized sources
of water, such as meltwater from highland ice sheets. Our results are
instead more consistent with an early Mars that supported widespread
precipitation and runoff.
Exocometary gas in_th_hd_181327_debris_ringSérgio Sacani
An increasing number of observations have shown that gaseous debris discs are not an
exception. However, until now we only knew of cases around A stars. Here we present the first
detection of 12CO (2-1) disc emission around an F star, HD 181327, obtained with ALMA
observations at 1.3 mm. The continuum and CO emission are resolved into an axisymmetric
disc with ring-like morphology. Using a Markov chain Monte Carlo method coupled with
radiative transfer calculations we study the dust and CO mass distribution. We find the dust is
distributed in a ring with a radius of 86:0 0:4 AU and a radial width of 23:2 1:0 AU. At
this frequency the ring radius is smaller than in the optical, revealing grain size segregation
expected due to radiation pressure. We also report on the detection of low level continuum
emission beyond the main ring out to 200 AU. We model the CO emission in the non-LTE
regime and we find that the CO is co-located with the dust, with a total CO gas mass ranging
between 1:2 10 6 M and 2:9 10 6 M, depending on the gas kinetic temperature and
collisional partners densities. The CO densities and location suggest a secondary origin, i.e.
released from icy planetesimals in the ring. We derive a CO cometary composition that is
consistent with Solar system comets. Due to the low gas densities it is unlikely that the gas is
shaping the dust distribution.
The importance of comets for the origin of life on Earth has been advocated for many decades. Amino acids are
key ingredients in chemistry, leading to life as we know it. Many primitive meteorites contain amino acids, and it
is generally believed that these are formed by aqueous alterations. In the collector aerogel and foil samples of the
Stardust mission after the flyby at comet Wild 2, the simplest form of amino acids, glycine, has been found
together with precursor molecules methylamine and ethylamine. Because of contamination issues of the samples,
a cometary origin was deduced from the 13C isotopic signature. We report the presence of volatile glycine
accompanied by methylamine and ethylamine in the coma of 67P/Churyumov-Gerasimenko measured by
the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) mass spectrometer, confirming the
Stardust results. Together with the detection of phosphorus and a multitude of organic molecules, this result
demonstrates that comets could have played a crucial role in the emergence of life on Earth.
Proper-motion age dating of the progeny of Nova Scorpii ad 1437Sérgio Sacani
‘Cataclysmic variables’ are binary star systems in which one
star of the pair is a white dwarf, and which often generate bright
and energetic stellar outbursts. Classical novae are one type of
outburst: when the white dwarf accretes enough matter from its
companion, the resulting hydrogen-rich atmospheric envelope
can host a runaway thermonuclear reaction that generates a rapid
brightening1–4. Achieving peak luminosities of up to one million
times that of the Sun5
, all classical novae are recurrent, on timescales
of months6
to millennia7
. During the century before and after an
eruption, the ‘novalike’ binary systems that give rise to classical
novae exhibit high rates of mass transfer to their white dwarfs8
.
Another type of outburst is the dwarf nova: these occur in binaries
that have stellar masses and periods indistinguishable from those
of novalikes9
but much lower mass-transfer rates10, when accretiondisk
instabilities11 drop matter onto the white dwarfs. The coexistence
at the same orbital period of novalike binaries and dwarf
novae—which are identical but for their widely varying accretion
rates—has been a longstanding puzzle9
. Here we report the recovery
of the binary star underlying the classical nova eruption of 11 March
ad 1437 (refs 12, 13), and independently confirm its age by propermotion
dating. We show that, almost 500 years after a classical-nova
event, the system exhibited dwarf-nova eruptions. The three other
oldest recovered classical novae14–16 display nova shells, but lack
firm post-eruption ages17,18, and are also dwarf novae at present.
We conclude that many old novae become dwarf novae for part of
the millennia between successive nova eruptions19,
A 50000 solar_mass_black_hole_in_the_nucleous_of_rgg_118Sérgio Sacani
Astrônomos usando o Observatório de Raios-X Chandra da NASA e o Telescópio Clay de 6.5 metros no Chile, identificaram o menor buraco negro supermassivo já detectado no centro de uma galáxia. Esse objeto paradoxal poderia fornecer pistas sobre qual o tamanho de buracos negros formados juntos com suas galáxias hospedeiras a 13 bilhões de anos atrás, ou mais.
Os astrônomos estimam que esse buraco negro supermassivo tem cerca de 50000 vezes a massa do Sol. Isso é menos da metade do buraco negro anterior de menor massa encontrado no centro de uma galáxia.
O buraco negro está localizado no centro do disco da galáxia anã, chamada de RGG 118, localizada a cerca de 340 milhões de anos-luz de distância da Terra. A imagem principal desse post, foi feita pelo Sloan Digital Sky Survey e o detalhe mostra uma imagem feita pelo Chandra do centro da galáxia. A fonte pontual de raios-X, é produzida pelo gás quente que faz um movimento de redemoinho ao redor do buraco negro.
Os pesquisadores estimaram a massa do buraco negro estudando o movimento do gás frio perto do centro da galáxia, usando dados na luz visível obtidos pelo Telescópio Clay. Eles usaram os dados do Chandra para descobrir o brilho em raios-X do gás quente espiralando na direção do buraco negro. Eles encontraram que a força de empurrão da pressão da radiação desse gás quente é equivalente a cerca de 1% da força de puxão da gravidade interna, o que se ajusta bem com as propriedades de outros buracos negros supermassivos.
Anteriormente, uma relação tinha sido notada entre a massa dos buracos negros supermassivos e o intervalo de velocidades das estrelas no centro da galáxia hospedeira. Essa relação também é mantida para a RGG 118 e seu buraco negro.
O buraco negro na RGG 118 é cerca de 100 vezes menos massivo do que o buraco negro supermassivo encontrado no centro da Via Láctea. Ele é também cerca de 200000 vezes menos massivo do que o buraco negro mais massivo já encontrado no centro de outras galáxias.
Os astrônomos estão tentando entender a formação de buracos negros com bilhões de vezes a massa solar que têm sido detectados a menos de um bilhão de anos depois do Big Bang. O buraco negro na RGG 118 dá aos astrônomos uma oportunidade de estudar um buraco negro supermassivo, pequeno e próximo, pertencente à primeira geração de buracos negros que não são detectáveis pela nossa tecnologia atual.
Os astrônomos acreditam que buracos negros supermassivos podem se formar quando grandes nuvens de gás, com uma massa entre 10000 e 100000 vezes a massa do Sol, colapsa num buraco negro. Muitos desses buracos negros semeiam então fusões para formar buracos negros supermassivos ainda maiores. De maneira alternativa, um buraco negro supermassivo poderia surgir de uma estrela gigante, com cerca de 100 vezes a massa do Sol, que no final da sua vida, depois de consumir todo o seu combustível, colapsa e forma um buraco negro.
Os pesquisadore
A Chandra X-ray study of millisecond pulsars in the globular cluster Omega Ce...Sérgio Sacani
Millisecond pulsars (MSPs) are faint X-ray sources commonly observed in Galactic globular clusters (GCs). In this work, we
investigate 18 MSPs newly found in the GC Omega Centauri (𝜔 Cen) and search for their X-ray counterparts using Chandra
observations with a total exposure time of 290.9 ks. We identify confident X-ray counterparts for 11 of the MSPs, with 9 of
them newly identified in this work based on their positions, spectral properties, and X-ray colours. The X-ray spectra of 9 MSPs
are well described by a neutron star hydrogen atmosphere model, while 2 MSPs are well fitted by a power-law model. The
identified MSPs have X-ray luminosities ranging from 1.0 × 1030 erg s−1
to 1.4 × 1031 erg s−1
. Additionally, for population
comparison purposes, we study the X-ray counterpart to MSP E in the GC M71, and find its X-ray spectrum is well described
by blackbody-like models with a luminosity of 1.9 × 1030 erg s−1
. We investigate the empirical correlations between X-ray
luminosities and minimum companion masses, as well as mass functions, of spider pulsars. Clear correlations are observed, with
best-fit functions of log10 𝐿𝑋 = (1.0 ± 0.1) log10 𝑀𝑐,𝑚𝑖𝑛 + (32.5 ± 0.2) and log10 𝐿𝑋 = (0.35 ± 0.04) log10 MF + (32.71 ± 0.20),
respectively, with an intrinsic scatter of log10 𝐿𝑋 of ∼0.3, where 𝐿𝑋 is the 0.5–10 keV X-ray luminosity, 𝑀𝑐,𝑚𝑖𝑛 is the minimum
companion mass, and MF represents the mass function, in solar masses.
A giant ring_like_structure_at_078_z_086_displayed_by_gr_bsSérgio Sacani
Uma equipe de astrônomos da Hungria e dos EUA descobriram o que parece ser a maior feição no universo observável: um anel de nove explosões de raios-gamma – e portanto, galáxias – com 5 bilhões de anos-luz de diâmetro. Os cientistas, liderados pelo Prof. Lajos Balazs, do Observatório Konkoloy, em Budapeste, reportou seu trabalho num artigo do Montlhy Notices of the Royal Astronomical Socitey.
Explosões de raios-Gamma as GRBs, são os eventos mais luminosos no universo, lançando o equivalente à energia que o Sol lança em 10 bilhões de anos em poucos segundos. Acredita-se que elas sejam o resultado do colapso de massivas estrelas em buracos negros. A grande luminosidade desses eventos, ajuda os astrônomos a mapearem o local de distantes galáxias, algo que a equipe explorou.
As GRBs que constituem o recém-descoberto anel foram observadas, usando uma grande variedade de telescópios, tanto em Terra como no espaço. Elas aparecem a uma distância muito similar de nós, cerca de 7 bilhões de anos-luz, num círculo de 36 graus através do nosso céu, ou o equivalente a mais de 70 vezes o diâmetro da Lua Cheia. Isso implica que o anel tem mais de 5 bilhões de anos-luz de diâmetro, e de acordo com o Professor Balazs, existe somente a probabilidade de 1 em 20000 das GRBs estarem nessa distribuição por coincidência.
A population of faint low surface brightness galaxies in the Perseus cluster ...Sérgio Sacani
We present the detection of 89 low surface brightness (LSB), and thus low stellar
density galaxy candidates in the Perseus cluster core, of the kind named ‘ultra-diffuse
galaxies’, with mean effective V-band surface brightnesses 24.8–27.1 mag arcsec−2
, total
V-band magnitudes −11.8 to −15.5 mag, and half-light radii 0.7–4.1 kpc. The candidates
have been identified in a deep mosaic covering 0.3 deg2
, based on wide-field
imaging data obtained with the William Herschel Telescope. We find that the LSB
galaxy population is depleted in the cluster centre and only very few LSB candidates
have half-light radii larger than 3 kpc. This appears consistent with an estimate of
their tidal radius, which does not reach beyond the stellar extent even if we assume
a high dark matter content (M/L = 100). In fact, three of our candidates seem to
be associated with tidal streams, which points to their current disruption. Given that
published data on faint LSB candidates in the Coma cluster – with its comparable central
density to Perseus – show the same dearth of large objects in the core region, we
conclude that these cannot survive the strong tides in the centres of massive clusters.
Hydrogen Column Density Variability in a Sample of Local Compton-Thin AGNSérgio Sacani
We present the analysis of multiepoch observations of a set of 12 variable, Compton-thin, local (z<0.1) active galactic nuclei (AGN) selected from the 100-month BAT catalog. We analyze all available X-ray data from Chandra, XMMNewton, and NuSTAR, adding up to a total of 53 individual observations. This corresponds to between 3 and 7 observations per source, probing variability timescales between a few days and ∼ 20 yr. All sources have at least one NuSTAR observation, ensuring high-energy coverage, which allows us to disentangle the line-of-sight and reflection components in the X-ray spectra. For each source, we model all available spectra simultaneously, using the physical torus models MYTorus, borus02, and UXCLUMPY. The simultaneous fitting, along with the high-energy coverage, allows us to place tight constraints on torus parameters such as the torus covering factor, inclination angle, and torus average column density. We also estimate the line-of-sight column density (NH) for each individual observation. Within the 12 sources, we detect clear line-of-sight NH variability in 5, non-variability in 5, and for 2 of them it is not possible to fully disentangle intrinsic-luminosity and NH variability. We observe large differences between the average values of line-ofsight NH (or NH of the obscurer) and the average NH of the torus (or NH of the reflector), for each source, by a factor between ∼ 2 to > 100. This behavior, which suggests a physical disconnect between the absorber and the reflector, is more extreme in sources that present NH variability. NH-variable AGN also tend to present larger obscuration and broader cloud distributions than their non-variable counterparts. We observe that large changes in obscuration only occur at long timescales, and use this to place tentative lower limits on torus cloud sizes.
Artigo descreve estudo feito com o Hubble que mostra o elo entre os buracos negros que apresentam os poderosos jatos relativísticos e galáxias massivas em fusão.
Exploring Proxies for the Supermassive Black Hole Mass Function: Implications...Sérgio Sacani
Supermassive black holes (SMBHs) reside at the center of every massive galaxy in the local universe with masses
that closely correlate with observations of their host galaxy, implying a connected evolutionary history. The
population of binary SMBHs, which form following galaxy mergers, is expected to produce a gravitational-wave
background (GWB) detectable by pulsar timing arrays (PTAs). PTAs are starting to see hints of what may be a
GWB, and the amplitude of the emerging signal is toward the higher end of model predictions. Simulated
populations of binary SMBHs can be constructed from observations of galaxies and are used to make predictions
about the nature of the GWB. The greatest source of uncertainty in these observation-based models comes from the
inference of the SMBH mass function, which is derived from observed host galaxy properties. In this paper, I
undertake a new approach for inferring the SMBH mass function, starting from a velocity dispersion function
rather than a galaxy stellar mass function. I argue that this method allows for a more direct inference by relying on
a larger suite of individual galaxy observations as well as relying on a more “fundamental” SMBH mass relation. I
find that the resulting binary SMBH population contains more massive systems at higher redshifts than previous
models. Additionally, I explore the implications for the detection of individually resolvable sources in PTA data.
Stellar-mass black holes in the Hyades star cluster?Sérgio Sacani
Astrophysical models of binary-black hole mergers in the Universe require a significant fraction of stellar-mass black holes (BHs)
to receive negligible natal kicks to explain the gravitational wave detections. This implies that BHs should be retained even in
open clusters with low escape velocities (≲ 1 km/s). We search for signatures of the presence of BHs in the nearest open cluster
to the Sun – the Hyades – by comparing density profiles of direct 𝑁-body models to data from Gaia. The observations are best
reproduced by models with 2−3 BHs at present. Models that never possessed BHs have an half-mass radius ∼ 30% smaller than
the observed value, while those where the last BHs were ejected recently (≲ 150 Myr ago) can still reproduce the density profile.
In 50% of the models hosting BHs, we find BHs with stellar companion(s). Their period distribution peaks at ∼ 103 yr, making
them unlikely to be found through velocity variations. We look for potential BH companions through large Gaia astrometric and
spectroscopic errors, identifying 56 binary candidates - none of which consistent with a massive compact companion. Models
with 2 − 3 BHs have an elevated central velocity dispersion, but observations can not yet discriminate. We conclude that the
present-day structure of the Hyades requires a significant fraction of BHs to receive natal kicks smaller than the escape velocity
of ∼ 3 km s−1
at the time of BH formation and that the nearest BHs to the Sun are in, or near, Hyades.
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.
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.
The physical conditions_in_a_pre_super_star_cluster_molecular_cloud_in_the_an...Sérgio Sacani
Artigo descreve estudo feitos pelos astrônomos utilizando o ALMA para descobrir um proto-aglomerado globular de estrelas gigantes se formando no interior das galáxias Antenas, o famoso par de galáxias em interação. É a primeira vez que os astrônomos conseguem observar um objeto desse tipo nos seus estágios iniciais de vida e com o ambiente ao redor inalterado.
Similar to Dwarf galaxies with_optical_signatures_of_active_massive_black_holes (20)
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
The solar dynamo begins near the surfaceSérgio Sacani
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
closely shadow sunspot migration, undoubtedly sharing a common cause2. Contrary
to theories suggesting deep origins of these phenomena, helioseismology pinpoints
low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface
shear layer3,4. Within this zone, inwardly increasing differential rotation coupled with
a poloidal magnetic field strongly implicates the magneto-rotational instability5,6,
prominent in accretion-disk theory and observed in laboratory experiments7.
Together, these two facts prompt the general question: whether the solar dynamo is
possibly a near-surface instability. Here we report strong affirmative evidence in stark
contrast to traditional models8 focusing on the deeper tachocline. Simple analytic
estimates show that the near-surface magneto-rotational instability better explains
the spatiotemporal scales of the torsional oscillations and inferred subsurface
magnetic field amplitudes9. State-of-the-art numerical simulations corroborate these
estimates and reproduce hemispherical magnetic current helicity laws10. The dynamo
resulting from a well-understood near-surface phenomenon improves prospects
for accurate predictions of full magnetic cycles and space weather, affecting the
electromagnetic infrastructure of Earth.
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Sérgio Sacani
The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy
was the construction of an observatory capable of characterizing habitable worlds. In this paper series
we explore the detectability of and interference from exomoons and exorings serendipitously observed
with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting
in this manuscript with Earth-Moon analog mutual events. Unlike transits, which only occur in systems
viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every
star-planet-moon system. The cadence of these events can vary widely from ∼yearly to multiple events
per day, as was the case in our younger Earth-Moon system. Leveraging previous space-based (EPOXI)
lightcurves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive
the detectability of Moon analogs with HWO. We determine that Earth-Moon analogs are detectable
with observation of ∼2-20 mutual events for systems within 10 pc, and larger moons should remain
detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet
features and weather. We find that HWO wavelength coverage in the near-IR, specifically in the 1.4 µm
water band where large moons can outshine their host planet, will aid in differentiating exomoon signals
from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin
to our Moon are more likely to be detected in younger systems, where shorter orbital periods and
favorable geometry enhance the probability and frequency of mutual events.
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...Sérgio Sacani
Mars is a particularly attractive candidate among known astronomical objects
to potentially host life. Results from space exploration missions have provided
insights into Martian geochemistry that indicate oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to
its toxicity. However, it can also provide potential benefits, such as producing
brines by deliquescence, like those thought to exist on present-day Mars. Here
we show perchlorate brines support folding and catalysis of functional RNAs,
while inactivating representative protein enzymes. Additionally, we show
perchlorate and other oxychlorine species enable ribozyme functions,
including homeostasis-like regulatory behavior and ribozyme-catalyzed
chlorination of organic molecules. We suggest nucleic acids are uniquely wellsuited to hypersaline Martian environments. Furthermore, Martian near- or
subsurface oxychlorine brines, and brines found in potential lifeforms, could
provide a unique niche for biomolecular evolution.
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
WASP-69b’s Escaping Envelope Is Confined to a Tail Extending at Least 7 RpSérgio Sacani
Studying the escaping atmospheres of highly irradiated exoplanets is critical for understanding the physical
mechanisms that shape the demographics of close-in planets. A number of planetary outflows have been observed
as excess H/He absorption during/after transit. Such an outflow has been observed for WASP-69b by multiple
groups that disagree on the geometry and velocity structure of the outflow. Here, we report the detection of this
planet’s outflow using Keck/NIRSPEC for the first time. We observed the outflow 1.28 hr after egress until the
target set, demonstrating the outflow extends at least 5.8 × 105 km or 7.5 Rp This detection is significantly longer
than previous observations, which report an outflow extending ∼2.2 planet radii just 1 yr prior. The outflow is
blueshifted by −23 km s−1 in the planetary rest frame. We estimate a current mass-loss rate of 1 M⊕ Gyr−1
. Our
observations are most consistent with an outflow that is strongly sculpted by ram pressure from the stellar wind.
However, potential variability in the outflow could be due to time-varying interactions with the stellar wind or
differences in instrumental precision.
X-rays from a Central “Exhaust Vent” of the Galactic Center ChimneySérgio Sacani
Using deep archival observations from the Chandra X-ray Observatory, we present an analysis of
linear X-ray-emitting features located within the southern portion of the Galactic center chimney,
and oriented orthogonal to the Galactic plane, centered at coordinates l = 0.08◦
, b = −1.42◦
. The
surface brightness and hardness ratio patterns are suggestive of a cylindrical morphology which may
have been produced by a plasma outflow channel extending from the Galactic center. Our fits of the
feature’s spectra favor a complex two-component model consisting of thermal and recombining plasma
components, possibly a sign of shock compression or heating of the interstellar medium by outflowing
material. Assuming a recombining plasma scenario, we further estimate the cooling timescale of this
plasma to be on the order of a few hundred to thousands of years, leading us to speculate that a
sequence of accretion events onto the Galactic Black Hole may be a plausible quasi-continuous energy
source to sustain the observed morphology
Let's dive deeper into the world of ODC! Ricardo Alves (OutSystems) will join us to tell all about the new Data Fabric. After that, Sezen de Bruijn (OutSystems) will get into the details on how to best design a sturdy architecture within ODC.
Neuro-symbolic is not enough, we need neuro-*semantic*Frank van Harmelen
Neuro-symbolic (NeSy) AI is on the rise. However, simply machine learning on just any symbolic structure is not sufficient to really harvest the gains of NeSy. These will only be gained when the symbolic structures have an actual semantics. I give an operational definition of semantics as “predictable inference”.
All of this illustrated with link prediction over knowledge graphs, but the argument is general.
Accelerate your Kubernetes clusters with Varnish CachingThijs Feryn
A presentation about the usage and availability of Varnish on Kubernetes. This talk explores the capabilities of Varnish caching and shows how to use the Varnish Helm chart to deploy it to Kubernetes.
This presentation was delivered at K8SUG Singapore. See https://feryn.eu/presentations/accelerate-your-kubernetes-clusters-with-varnish-caching-k8sug-singapore-28-2024 for more details.
Connector Corner: Automate dynamic content and events by pushing a buttonDianaGray10
Here is something new! In our next Connector Corner webinar, we will demonstrate how you can use a single workflow to:
Create a campaign using Mailchimp with merge tags/fields
Send an interactive Slack channel message (using buttons)
Have the message received by managers and peers along with a test email for review
But there’s more:
In a second workflow supporting the same use case, you’ll see:
Your campaign sent to target colleagues for approval
If the “Approve” button is clicked, a Jira/Zendesk ticket is created for the marketing design team
But—if the “Reject” button is pushed, colleagues will be alerted via Slack message
Join us to learn more about this new, human-in-the-loop capability, brought to you by Integration Service connectors.
And...
Speakers:
Akshay Agnihotri, Product Manager
Charlie Greenberg, Host
UiPath Test Automation using UiPath Test Suite series, part 3DianaGray10
Welcome to UiPath Test Automation using UiPath Test Suite series part 3. In this session, we will cover desktop automation along with UI automation.
Topics covered:
UI automation Introduction,
UI automation Sample
Desktop automation flow
Pradeep Chinnala, Senior Consultant Automation Developer @WonderBotz and UiPath MVP
Deepak Rai, Automation Practice Lead, Boundaryless Group and UiPath MVP
Essentials of Automations: Optimizing FME Workflows with ParametersSafe Software
Are you looking to streamline your workflows and boost your projects’ efficiency? Do you find yourself searching for ways to add flexibility and control over your FME workflows? If so, you’re in the right place.
Join us for an insightful dive into the world of FME parameters, a critical element in optimizing workflow efficiency. This webinar marks the beginning of our three-part “Essentials of Automation” series. This first webinar is designed to equip you with the knowledge and skills to utilize parameters effectively: enhancing the flexibility, maintainability, and user control of your FME projects.
Here’s what you’ll gain:
- Essentials of FME Parameters: Understand the pivotal role of parameters, including Reader/Writer, Transformer, User, and FME Flow categories. Discover how they are the key to unlocking automation and optimization within your workflows.
- Practical Applications in FME Form: Delve into key user parameter types including choice, connections, and file URLs. Allow users to control how a workflow runs, making your workflows more reusable. Learn to import values and deliver the best user experience for your workflows while enhancing accuracy.
- Optimization Strategies in FME Flow: Explore the creation and strategic deployment of parameters in FME Flow, including the use of deployment and geometry parameters, to maximize workflow efficiency.
- Pro Tips for Success: Gain insights on parameterizing connections and leveraging new features like Conditional Visibility for clarity and simplicity.
We’ll wrap up with a glimpse into future webinars, followed by a Q&A session to address your specific questions surrounding this topic.
Don’t miss this opportunity to elevate your FME expertise and drive your projects to new heights of efficiency.
UiPath Test Automation using UiPath Test Suite series, part 4DianaGray10
Welcome to UiPath Test Automation using UiPath Test Suite series part 4. In this session, we will cover Test Manager overview along with SAP heatmap.
The UiPath Test Manager overview with SAP heatmap webinar offers a concise yet comprehensive exploration of the role of a Test Manager within SAP environments, coupled with the utilization of heatmaps for effective testing strategies.
Participants will gain insights into the responsibilities, challenges, and best practices associated with test management in SAP projects. Additionally, the webinar delves into the significance of heatmaps as a visual aid for identifying testing priorities, areas of risk, and resource allocation within SAP landscapes. Through this session, attendees can expect to enhance their understanding of test management principles while learning practical approaches to optimize testing processes in SAP environments using heatmap visualization techniques
What will you get from this session?
1. Insights into SAP testing best practices
2. Heatmap utilization for testing
3. Optimization of testing processes
4. Demo
Topics covered:
Execution from the test manager
Orchestrator execution result
Defect reporting
SAP heatmap example with demo
Speaker:
Deepak Rai, Automation Practice Lead, Boundaryless Group and UiPath MVP
Kubernetes & AI - Beauty and the Beast !?! @KCD Istanbul 2024Tobias Schneck
As AI technology is pushing into IT I was wondering myself, as an “infrastructure container kubernetes guy”, how get this fancy AI technology get managed from an infrastructure operational view? Is it possible to apply our lovely cloud native principals as well? What benefit’s both technologies could bring to each other?
Let me take this questions and provide you a short journey through existing deployment models and use cases for AI software. On practical examples, we discuss what cloud/on-premise strategy we may need for applying it to our own infrastructure to get it to work from an enterprise perspective. I want to give an overview about infrastructure requirements and technologies, what could be beneficial or limiting your AI use cases in an enterprise environment. An interactive Demo will give you some insides, what approaches I got already working for real.
Dev Dives: Train smarter, not harder – active learning and UiPath LLMs for do...UiPathCommunity
💥 Speed, accuracy, and scaling – discover the superpowers of GenAI in action with UiPath Document Understanding and Communications Mining™:
See how to accelerate model training and optimize model performance with active learning
Learn about the latest enhancements to out-of-the-box document processing – with little to no training required
Get an exclusive demo of the new family of UiPath LLMs – GenAI models specialized for processing different types of documents and messages
This is a hands-on session specifically designed for automation developers and AI enthusiasts seeking to enhance their knowledge in leveraging the latest intelligent document processing capabilities offered by UiPath.
Speakers:
👨🏫 Andras Palfi, Senior Product Manager, UiPath
👩🏫 Lenka Dulovicova, Product Program Manager, UiPath
JMeter webinar - integration with InfluxDB and GrafanaRTTS
Watch this recorded webinar about real-time monitoring of application performance. See how to integrate Apache JMeter, the open-source leader in performance testing, with InfluxDB, the open-source time-series database, and Grafana, the open-source analytics and visualization application.
In this webinar, we will review the benefits of leveraging InfluxDB and Grafana when executing load tests and demonstrate how these tools are used to visualize performance metrics.
Length: 30 minutes
Session Overview
-------------------------------------------
During this webinar, we will cover the following topics while demonstrating the integrations of JMeter, InfluxDB and Grafana:
- What out-of-the-box solutions are available for real-time monitoring JMeter tests?
- What are the benefits of integrating InfluxDB and Grafana into the load testing stack?
- Which features are provided by Grafana?
- Demonstration of InfluxDB and Grafana using a practice web application
To view the webinar recording, go to:
https://www.rttsweb.com/jmeter-integration-webinar
LF Energy Webinar: Electrical Grid Modelling and Simulation Through PowSyBl -...DanBrown980551
Do you want to learn how to model and simulate an electrical network from scratch in under an hour?
Then welcome to this PowSyBl workshop, hosted by Rte, the French Transmission System Operator (TSO)!
During the webinar, you will discover the PowSyBl ecosystem as well as handle and study an electrical network through an interactive Python notebook.
PowSyBl is an open source project hosted by LF Energy, which offers a comprehensive set of features for electrical grid modelling and simulation. Among other advanced features, PowSyBl provides:
- A fully editable and extendable library for grid component modelling;
- Visualization tools to display your network;
- Grid simulation tools, such as power flows, security analyses (with or without remedial actions) and sensitivity analyses;
The framework is mostly written in Java, with a Python binding so that Python developers can access PowSyBl functionalities as well.
What you will learn during the webinar:
- For beginners: discover PowSyBl's functionalities through a quick general presentation and the notebook, without needing any expert coding skills;
- For advanced developers: master the skills to efficiently apply PowSyBl functionalities to your real-world scenarios.
1. Draft version August 13, 2013
A
Preprint typeset using L TEX style emulateapj v. 5/2/11
DWARF GALAXIES WITH OPTICAL SIGNATURES OF ACTIVE MASSIVE BLACK HOLES
Amy E. Reines1
National Radio Astronomy Observatory, Charlottesville, VA 22903, USA
Jenny E. Greene
arXiv:1308.0328v2 [astro-ph.CO] 12 Aug 2013
Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
and
Marla Geha
Department of Astronomy, Yale University, New Haven, CT 06520, USA
Draft version August 13, 2013
ABSTRACT
We present a sample of 151 dwarf galaxies (108.5
M
109.5 M ) that exhibit optical spectroscopic signatures of accreting massive black holes (BHs), increasing the number of known active
galaxies in this stellar mass range by more than an order of magnitude. Utilizing data from the Sloan
Digital Sky Survey Data Release 8 and stellar masses from the NASA-Sloan Atlas, we have systematically searched for active BHs in ∼25,000 emission-line galaxies with stellar masses comparable to
the Magellanic Clouds and redshifts z < 0.055. Using the narrow-line [O III]/Hβ versus [N II]/Hα
diagnostic diagram, we find photoionization signatures of BH accretion in 136 galaxies, a small fraction of which also exhibit broad Hα emission. For these broad-line AGN candidates, we estimate BH
masses using standard virial techniques and find a range of 105
MBH
106 M and a median of
5
MBH ∼ 2 × 10 M . We also detect broad Hα in 15 galaxies that have narrow-line ratios consistent
with star-forming galaxies. Follow-up observations are required to determine if these are true type 1
AGN or if the broad Hα is from stellar processes. The median absolute magnitude of the host galaxies
in our active sample is Mg = −18.1 mag, which is ∼1–2 magnitudes fainter than previous samples of
AGN hosts with low-mass BHs. This work constrains the smallest galaxies that can form a massive
BH, with implications for BH feedback in low-mass galaxies and the origin of the first supermassive
BH seeds.
Subject headings: galaxies: active — galaxies: dwarf — galaxies: nuclei— galaxies: Seyfert
1. INTRODUCTION
Over the past decade we have come to appreciate that
nuclear black holes (BHs) with MBH ∼ 106 − 109 M
are a ubiquitous component of massive galaxies in the
modern Universe (e.g., Kormendy & Richstone 1995; Kormendy & Ho 2013), yet the origin of the first highredshift supermassive BH “seeds” is far from understood.
Observations of quasars with billion solar-mass BHs at a
time when the Universe was less than a Gyr old (e.g., Fan
et al. 2001; Mortlock et al. 2011) demonstrate that supermassive BHs almost certainly started out with masses
considerably in excess of normal stellar-mass BHs. However, we do not know how these initial seed BHs formed
in the early Universe, how massive they were originally,
or in what types of galaxies they formed. While direct
observations of distant seed BHs and their host galaxies in the infant Universe are unobtainable with current
capabilities, nearby dwarf galaxies are within observational reach and can provide important constraints on
the formation path, masses and hosts of BH seeds (e.g.,
Volonteri 2010; Greene 2012). The goal of this work is
to systematically search for optical AGN signatures in
dwarf galaxies (M
3 × 109 M ), where very few mas-
areines@nrao.edu
1 Einstein Fellow
sive BHs2 have hitherto been found.
The growth of supermassive BHs appears to be linked
to the evolution of their hosts, with more massive galaxies generally harboring more massive BHs (e.g., Gebhardt et al. 2000a; Ferrarese & Merritt 2000; Marconi
& Hunt 2003; G¨ltekin et al. 2009; McConnell & Ma
u
2013). Therefore, unlike today’s massive galaxies, lowmass dwarf galaxies with relatively quiet merger histories may host BHs with masses not so different from the
first seed BHs (Bellovary et al. 2011). Models of BH
growth in a cosmological context (Volonteri et al. 2008)
indicate that if we can determine the BH occupation fraction and mass distribution in present-day dwarf galaxies,
we will gain insight into whether seed BHs formed primarily as the end-product of Population III stars (e.g.,
Bromm & Yoshida 2011), in a direct collapse scenario
(e.g., Haehnelt & Rees 1993; Lodato & Natarajan 2006;
Begelman et al. 2006), or in a runaway accretion event at
the center of a dense star cluster (e.g., Portegies Zwart
et al. 2004; Miller & Davies 2012). Studying the scaling relations between BHs and galaxies at low-mass may
provide further clues (e.g., Volonteri & Natarajan 2009).
There are additional reasons to search for and study
2 We use the term “massive BH” to refer to BHs larger than
normal stellar-mass BHs. BHs with masses in the range ∼ 104 −
106 M are also sometimes referred to as “low-mass BHs” (meaning relatively low-mass supermassive BHs) or “intermediate-mass
BHs (IMBHs).”
2. 2
Reines et al.
massive BHs in dwarf galaxies. Understanding the radiative properties of BHs in this mass range is important
for models of the impact of mini-quasars on reionization
and the formation of the first galaxies (e.g., Milosavljevi´ et al. 2009). Moreover, the study of BH accrec
tion and star formation in low-mass dwarfs today may
prove a good laboratory for understanding their interplay at early times (e.g., Reines et al. 2011; Jia et al.
2011; Alexandroff et al. 2012) and the apparent contribution of obscured AGNs in blue low-mass galaxies to the
cosmic X-ray background (Xue et al. 2012). Determining
the presence of AGN in low-mass galaxies will also help
constrain BH feedback and galaxy formation models at
all mass scales. For instance, while BH feedback is often
invoked to explain star formation quenching in massive
galaxies (e.g., Croton et al. 2006; Kimm et al. 2009), the
quenched fraction of central galaxies decreases with stellar mass (Wetzel et al. 2012) and may become zero below a stellar mass near 109 M (Kauffmann et al. 2003a;
Geha et al. 2012). Finally, signatures of tidal disruptions
of stars are strongest for low-mass BHs (e.g., Strubbe &
Quataert 2009; Rosswog et al. 2009; Miller & G¨ltekin
u
2011) and ∼ 105 M BH mergers have the right frequency to provide a signal for future gravitational wave
experiments (e.g., Hughes 2002).
The most secure method of discovering supermassive
BHs uses stellar or gas dynamics to weigh the central BH (see review in Kormendy 2004). However, the
gravitational sphere of influence cannot be resolved for
low-mass BHs in small galaxies much beyond the Local
Group. For example, rinfl = GMBH /σ 2 ∼ 0.5 pc assuming MBH ∼ 105 M and a stellar velocity dispersion of
σ ∼ 30 km s−1 . Even with the resolution afforded by
the Hubble Space Telescope (HST) or adaptive optics on
large ground-based telescopes, such a small radius of influence can only be resolved out to a distance of ∼ 1 Mpc.
Nevertheless, there are limits on dynamical BH masses
and a couple of detections in nearby low-mass galaxies.
The Local Group galaxies NGC 205 (a bright early-type
dwarf satellite of Andromeda), Ursa Minor, and Fornax
(both classical dwarf spheroidals around the Milky Way)
all have upper limits of MBH
a few ×104 M from
stellar dynamics (Valluri et al. 2005; Lora et al. 2009;
Jardel & Gebhardt 2012). In contrast, the low-mass elliptical M32 has a BH with MBH ∼ a few ×106 M
(e.g., Dressler & Richstone 1988; van der Marel et al.
1998). NGC 404, a low-mass S0 just beyond the Local
Group, also has a likely BH with MBH ∼ 5 × 105 M
derived from molecular hydrogen gas kinematics (Seth
et al. 2010). A number of very late-type spiral galaxies have dynamical BH mass limits, including M33 with
MBH a few ×103 M (Gebhardt et al. 2001). Outside
the Local Group, Barth et al. (2009) find a conservative
upper limit of MBH
3 × 106 M on the active BH in
NGC 3621, while Neumayer & Walcher (2012) find upper
limits of ∼ 106 M for nine more late-type spirals.
In more distant systems, and in particular those with
low-mass BHs, obtaining dynamical evidence for a BH is
not feasible and we must rely on radiative signatures of
AGN powered by BH accretion. The dwarf spiral galaxy
NGC 4395 (M ∼ 1.3 × 109 M ), for example, has clear
and unambiguous evidence for a central BH from highionization narrow emission lines and broad permitted
lines in the optical (Filippenko & Sargent 1989), a compact radio jet (Wrobel & Ho 2006), and extreme variability in the X-ray (Vaughan et al. 2005; Moran et al. 2005).
NGC 4395 is not just a fluke; POX 52 is dwarf elliptical
(M ∼ 1.2×109 M ; Thornton et al. 2008) with an AGN
that is very similar in optical properties to NGC 4395
(Kunth et al. 1987; Barth et al. 2004). These two dwarf
galaxies have BH mass estimates of MBH ∼ 3 × 105 M
(Filippenko & Ho 2003; Peterson et al. 2005; Thornton
et al. 2008).
Reines et al. (2011) present multi-wavelength evidence
for the first example of a massive BH in a dwarf starburst galaxy, Henize 2-10, which has an irregular central
morphology and no discernible bulge. The evidence for
an accreting massive BH includes Very Large Array radio and Chandra hard X-ray point sources at the center
of the galaxy and clearly separated from the bright H II
regions. Follow-up Very Long Baseline Interferometry
(VLBI) observations reveal parsec-scale non-thermal radio continuum from the precise location of the putative
active nucleus (Reines & Deller 2012) and no star clusters
are seen at this location in HST observations. The source
lies at the center of a ∼250-pc-long ionized gas structure
that is suggestive of bipolar flow and the position of the
central source is consistent with the dynamical center of
the galaxy. Reines et al. (2011) estimate a BH mass of
log (MBH /M ) = 6.3 ± 1.1 using the radio–X-ray–MBH
fundamental plane (Merloni et al. 2003), and Kormendy
& Ho (2013) estimate that Henize 2-10 has a stellar mass
of M ∼ 1.4 × 109 M with an uncertainty of a factor of
3. To determine the frequency of objects like NGC 4395,
Pox 52, and Henize 2-10 requires large surveys for AGN
signatures in low-mass galaxies.
In an effort to find AGNs with low-mass BHs, Greene
& Ho (2004, 2007a), and Dong et al. (2012) searched systematically through the Sloan Digital Sky Survey (SDSS;
York et al. 2000) for broad Hα, as a signature that an
accreting BH is present. They present samples of > 200
galaxies with MBH 106.5 M and median BH masses of
MBH ∼ 1 × 106 M . In a complementary search, Barth
et al. (2008) present a sample of narrow-line AGN in
host galaxies with relatively low stellar velocity dispersions, suggesting the presence of low-mass BHs. However, the vast majority of galaxies in all of these samples are more massive than M ∼ 109 M , and thus do
not probe the dwarf galaxy regime (Barth et al. 2008;
Greene et al. 2008; Jiang et al. 2011). Determining the
true space densities of low-mass BHs from the SDSS surveys is very difficult because of the joint bias towards
luminous galaxies (for spectroscopic targeting) and luminous AGNs (for spectroscopic identification; Greene &
Ho 2007b). Searches based on mid-infrared (e.g., Spitzer
spectroscopy; Satyapal et al. 2007, 2008, 2009; Goulding
et al. 2010) or X-ray observations (Ghosh et al. 2008;
Desroches & Ho 2009; Gallo et al. 2008, 2010; Kamizasa
et al. 2012; Miller et al. 2012; Schramm et al. 2013) have
so far covered only small volumes, often with heterogeneous selection.
So far there has been no systematic look at the AGN
population in dwarf galaxies. Previous AGN studies have
looked at galaxies with stellar masses typically larger
than ∼ 1010 M . Here we undertake the first systematic search for active massive BHs in dwarf galaxies with
3. Dwarf Galaxies with Active Massive Black Holes
stellar masses comparable to or less than the Large Magellanic Cloud (LMC). Starting with a sample of ∼ 25, 000
emission-line galaxies in the SDSS Data Release 8 (DR8)
spectroscopic catalog (Aihara et al. 2011) with stellar
masses M
3 × 109 M and redshifts z < 0.055, we
identify dwarf galaxies with narrow-line photoionization
signatures of an accreting massive BH. In addition, we
search for broad Hα emission that may indicate gas orbiting in the deep potential well of a massive BH. Collectively, the galaxies presented here are the smallest and
least-massive known to contain massive BHs.
2. DATA AND DWARF GALAXY SAMPLE
We have selected our sample of dwarf galaxies from
the NASA-Sloan Atlas3 (NSA), which in turn is based on
the SDSS DR8 spectroscopic catalog (York et al. 2000;
Aihara et al. 2011). We use the NSA for selecting our
parent sample of galaxies and investigating galaxy properties, but analyze the SDSS spectra with our own customized software to search for signatures of BH accretion (Section 3). The SDSS uses the dedicated 2.5-meter
wide-field Sloan Foundation Telescope and a 640-fiber
double spectrograph at Apache Point Observatory in
New Mexico (Gunn et al. 2006). The instrumental fiber
diameter is 3 and the spectrophotometrically calibrated
spectra cover a wavelength range from 3800 − 9200 ˚,
A
with a instrumental dispersion of 69 km s−1 per pixel.
The NSA provides a re-analysis of the SDSS imaging and spectroscopic data for all galaxies with redshifts
z < 0.055. Photometry is improved over the standard
SDSS DR8 photometric catalog as described in Blanton et al. (2011) and results in a cleaner sample of
dwarf galaxies compared to previous catalogs that include many fragmented pieces of extended massive galaxies. The spectroscopic data is re-analyzed using the
methods of Yan & Blanton (2012) and Yan (2011). We
only use the emission line measurements in the NSA for
quality cuts in signal-to-noise and equivalent width as
described below. In addition to a variety of galaxy parameters, estimates of stellar masses are provided in the
NSA. Stellar masses are derived from the kcorrect code
of Blanton & Roweis (2007), which fits broadband fluxes
using templates based on the stellar population synthesis models of Bruzual & Charlot (2003) and the nebular
emission-line models of Kewley et al. (2001). Masses are
given in units of M h−2 and we have assumed h = 0.73.
Since our goal is to search for dwarf galaxies hosting
active massive BHs, we first select sources in the NSA
with stellar masses M ≤ 3 × 109 M and obtain 44,594
objects. Our mass threshold, while somewhat arbitrary,
is approximately equal to the stellar mass of the LMC
(van der Marel et al. 2002), which is the most massive
dwarf galaxy satellite around the Milky Way. While we
do not apply a minimum stellar mass limit, nearly all of
the galaxies in our parent sample have M
107 M due
to the SDSS spectroscopic apparent magnitude limit of
r < 17.7. Therefore, while we can probe dwarf galaxies
with stellar masses comparable to the Magellanic Clouds,
we are not sensitive to galaxies with lower stellar mass
such as the Fornax dwarf spheroidal (2×107 M ) around
the Milky Way (e.g., McConnachie 2012; Mateo 1998).
We also impose modest requirements on emission line
3
http://www.nsatlas.org
3
flux measurements reported in the NSA: a signal-to-noise
ratio S/N ≥ 3 and an equivalent width EW > 1 for Hα,
[N II] λ6584, and [O III] λ5007 and S/N ≥ 2 for Hβ. This
reduces the number of sources to 25,974.
We use stellar mass as our primary selection criterion rather than absolute magnitude since galaxies of a
given mass can span a wide range in absolute magnitude
due to differences in stellar populations. Younger, bluer,
star-forming galaxies will be brighter than older, redder, quenched galaxies for a given mass (e.g., Bell et al.
2003). Additionally, strong emission lines (and even nebular continuum) can boost broad-band fluxes, especially
in the SDSS g- and r-bands (e.g., Reines et al. 2010; Anders & Fritze-v. Alvensleben 2003). Therefore, imposing
an absolute magnitude cut would preferentially exclude
line-emitting galaxies compared to equivalent galaxies
that do not have strong emission lines. The derived stellar masses are less sensitive to these effects since multiple bands are fit and the SED templates of Blanton &
Roweis (2007) include emission lines. However, imposing
a stellar mass cut introduces a bias such that blue/starforming galaxies will be detected over a larger volume
than red/quenched galaxies with the same stellar mass
(e.g., Geha et al. 2012).
3. ANALYSIS AND RESULTS
There are many ways to identify the presence of an accreting supermassive BH (see the review in Ho 2008). In
this work, we search for two signatures of active BHs in
the optical spectra of galaxies: 1) narrow emission-line
ratios indicating photoionization by an accreting BH, and
2) broad Hα emission signifying dense gas orbiting a massive BH. After selecting dwarf emission-line galaxies from
the NSA (§2), we retrieve the SDSS spectra for the entire
sample and analyze them with customized software as described below. All code was developed in the Interactive
Data Language (IDL) and our fitting routines make use
of the non-linear least squares curve fitting package MPFIT (Markwardt 2009). Individual sources flagged by
our automated algorithms are subsequently inspected by
eye.
3.1. Continuum and Absorption Line Subtraction
Before we can look for any signature of an AGN, we
need to model and remove stellar continuum from the
host galaxy, that in almost all cases dominates the total
continuum. The spectra also contain stellar absorption
lines. Balmer absorption is of particular concern since we
aim to detect potentially weak broad Hα emission from
nuclear activity in the galaxies. Our general approach
for modeling the continuum and absorption lines is based
on that presented in Tremonti et al. (2004). We fit the
galaxy spectra with a non-negative linear combination of
simple stellar population (SSP) models spanning a range
of ages for a given metallicity. The model templates are
the same as those used in Tremonti et al. (2004) and come
from the stellar population synthesis code of Bruzual &
Charlot (2003)4 . The templates include model spectra
for 10 different ages (0.005, 0.025, 0.1, 0.29, 0.64, 0.9,
1.4, 2.5, 5, and 11 Gyr) and 3 different metallicities (Z
= 0.008, 0.02, 0.05). Each galaxy spectrum is modeled as
4 We retrieved the templates from the corresponding website
http://www2.iap.fr/users/charlot/bc2003/.
4. 4
Reines et al.
a combination of SSP templates with a single metallicity
and we select the metallicity yielding the best-fit. In the
fitting process, we allow for reddening from dust using
the Galactic extinction curve of Cardelli et al. (1989) and
Gaussian smoothing to match the absorption line widths.
Our algorithm for modeling the continuum and absorption lines in each spectrum is an iterative process. The
SSP models do not contain emission lines and so we begin by masking out pixels 5σ above the continuum in
the observed spectra to remove both strong and weak
lines. We then apply a redshift-correction using the redshift derived from emission lines provided in the NSA
catalog. A preliminary model is fit to the resulting spectrum and the two are cross-correlated to determine any
redshift offset between the absorption and emission lines.
After correcting for the redshift offset, we find the best fit
model for each of the 3 model metallicities. The singlemetallicity model with the smallest χ2 value is selected
and used to improve the masking of emission lines. Pixels more than 5σ above the difference spectrum (data −
model) are excluded in the last round of fitting. Again,
we find the best-fit model for each metallicity and select
the single-metallicity model with the smallest χ2 for our
final model of the continuum and absorption line spectrum. The vast majority of the galaxy spectra are best
fit by the sub-solar metallicity model (Z = 0.008), which
is consistent with studies demonstrating that low-mass
galaxies generally have low metallicities (e.g. Tremonti
et al. 2004). In the small fraction of cases where absorption lines are either extremely weak or absent, a thirdorder polynomial is fit to the continuum. We subtract
this model from the data to produce a pure-emission line
spectrum.
3.2. Emission Line Measurements
In order to identify the spectral signatures of active
massive BHs, we model the emission lines of interest as
Gaussians. We are especially interested in detecting any
possible broad Hα component. Luminous unobscured
AGN powered by supermassive BHs in massive galaxies
often exhibit bright, broad Hα emission that is clearly
visible even by eye. However, the broad Hα signatures
from AGNs with lower-mass BHs hosted by dwarf galaxies will be less pronounced, generally having narrower
widths and lower luminosities than their higher mass
counterparts. Moreover, any potential broad Hα feature
will be blended with narrow Hα emission and the surrounding [N II] λλ6548, 6583 doublet. Therefore, it is
vital to carefully model the narrow emission line profile
in order to detect any potential broad Hα emission.
We base our model of the narrow emission line profile
on the [S II] λλ6713, 6731 doublet, which has been shown
to be generally well-matched to the line profiles of the
[N II] λλ6548, 6583 doublet and narrow Hα (Filippenko
& Sargent 1988, 1989; Ho et al. 1997; Greene & Ho 2004).
The [S II] doublet is first fit with a single Gaussian model
with the width of the two lines assumed to be equal and
the relative separation between the two lines held fixed by
their laboratory wavelengths. The [S II] doublet is also fit
with a two-component Gaussian model, with the added
constraint that the height ratio of the two components
must be equal for each line. If the reduced χ2 value from
the two-component model is at least 10% lower than that
of the single Gaussian model, the two-component model
is selected. Nearly all of the galaxies in our dwarf sample
only require a single Gaussian to model the [S II] doublet,
with only 15 sources preferring a two-component model
(8 of which turn out to be classified as either a BPT AGN
or composite, see Section 3.3).
Once we have constructed a suitable model of the [S II]
doublet, we use it as a template for fitting the narrow
lines in the Hα + [N II] complex. The relative separations between the centroids of the narrow Gaussian components are held fixed using laboratory wavelengths and
the flux of [N II] λ6584 to [N II] λ6548 is fixed at the
theoretical value of 2.96. We assume the [N II] lines have
the same width (in velocity) as the [S II] lines, but generously allow the width of the narrow Hα component to increase by as much as 25% for the vast majority of cases in
which a single Gaussian is used to model the narrow line
profile. For the small number of sources (15/25974) with
two-component Gaussian models for the narrow lines, the
profiles are strictly scaled from the [S II] lines. The Hα +
[N II] complex is fit and the reduced χ2 computed. The
Hα + [N II] complex is fit a second time, allowing for an
additional broad Hα component. If the resulting reduced
χ2 is improved by at least 20% and the FWHM of the
broad Hα component is at least 500 km s−1 after correcting for the fiber-dependent instrumental resolution,
we select the model including broad Hα. Our choice of
20% improvement in reduced χ2 , while somewhat arbitrary, has been used successfully in previous studies (e.g.,
Hao et al. 2005) and empirically works here. The modest
FWHM requirement is imposed to avoid severe contamination from galaxies undergoing intense star formation
that have moderately broadened bases on Hα. The procedures described thus far yields a sample of 51 sources
flagged as having a broad Hα component, not all of which
make it into our final sample of broad-line AGN candidates as described in Section 3.4.
We also measure the Hβ, [O III] λ5007 and [O I] 6300
emission lines. The narrow-line profile derived from the
[S II] doublet is used as a template for fitting Hβ, using
the same approach as that for Hα. The Hβ line is fit
twice, with and without a broad component. If statistically justified (reduced χ2 is improved by at least 20%),
we accept the model with a broad component. Since the
[O III] profile commonly exhibits a broad, blue shoulder
(e.g., Heckman et al. 1981; Whittle 1985) and does not
typically match the profile of the other narrow lines measured in this work (Greene & Ho 2005a), we do not use
the model derived from the [S II] doublet. Instead, we fit
the [O III] (and [O I]) line independently allowing for up
to two Gaussian components (χ2 must be reduced by at
least 20% to use the two-component model).
Emission-line fluxes are calculated using the Gaussian
model parameters. Uncertainties in the model parameters are provided by MPFIT, which accounts for the
SDSS error spectrum. We use standard propagation of
errors to determine the errors in the line fluxes.
3.3. BPT AGN and Composites
When an accreting BH is present in a galaxy, the ISM is
photoionized by a much harder continuum than is emitted by hot stars. AGNs and H II regions separate cleanly
in two-dimensional strong line diagnostic diagrams that
take pairs of lines close together in frequency to mitigate
5. Dwarf Galaxies with Active Massive Black Holes
5
Figure 1. Left: BPT [O III]/Hβ versus [N II]/Hα narrow-line diagnostic diagram for all ∼ 25, 000 dwarf emission-line galaxies analyzed
in this work. Galaxies with spectra dominated by an AGN are plotted as red points and galaxies with spectra dominated by star formation
are plotted as blue points. Composite galaxies with significant contributions from both an AGN and star formation are plotted as purple
points. The typical error is shown in the lower right corner (individual flux errors are given in Tables 2 and 4). The dashed line is an
empirical separation of pure star-forming galaxies and those with some contribution from an AGN from Kauffmann et al. (2003b). The
solid line is from Kewley et al. (2001), indicating the ‘maximum starburst line’ given by pure stellar photoionization models. We note
that the red point falling to the far left of the diagram and just above the dividing line is unusual in a number of ways and rather suspect
(see footnote in text). Right: BPT diagram for broad-line AGN candidates only (§3.4). We consider the sources falling in the AGN and
composite regions of the diagram the most secure broad-line candidates. Significant contamination from luminous Type II supernovae is
likely in the star-forming region of the diagram.
the effects of reddening (Baldwin et al. 1981; Veilleux &
Osterbrock 1987; Kewley et al. 2001; Kauffmann et al.
2003b; Kewley et al. 2006). The two-dimensional linediagnostic diagrams (also known as BPT diagrams after
the Baldwin et al. paper) are routinely used to separate
line-emitting galaxies by their primary excitation source.
Here we employ the most widely used BPT diagram
as our primary diagnostic, which takes [O III]/Hβ vs.
[N II]/Hα (Figure 1). In this diagram, line-emitting
galaxies separate into a V -shape (e.g., Kewley et al.
2006; Groves et al. 2006). Star-forming galaxies with
H II-region-like spectra occupy the left-most plume of
galaxies, with lower-metallicity systems having higher
[O III]/Hβ ratios and lower [N II]/Hα ratios (e.g., Moustakas et al. 2006). AGNs occupy the right branch of
galaxies with high-ionization Seyferts found in the upper right. Low-metallicity AGNs are found to the left
of the main Seyfert region and can overlap with lowmetallicity starburst galaxies (Groves et al. 2006; Ludwig et al. 2012). The most contentious region of the
diagram sits directly below the Seyfert galaxies: galaxies with very high low-ionization lines, named Low Ionization Nuclear Emission Region galaxies by Heckman
(LINERs; 1980). LINER emission can be generated both
by shocks and very hard AGN spectra, and disentangling
the primary origin in any given case can be complicated
and aperture dependent (e.g., Kewley et al. 2006; Sarzi
et al. 2006; Ho 2008; Eracleous et al. 2010; Yan & Blanton 2012). Finally, composites objects fall in the region
delineated by the empirical dividing line of Kauffmann
et al. (2003b) separating pure star-forming galaxies from
those with some contribution from an AGN, and the theoretical ‘maximum starburst line’ of Kewley et al. (2001)
given by pure stellar photoionization models. Composite
objects are thought to contain significant contributions
from both AGN and star formation (e.g., Panessa et al.
2005; Kewley et al. 2006; Trouille et al. 2011, but also
see Liu et al. (2008)).
Using the [O III]/Hβ vs. [N II]/Hα diagnostic diagram
and our narrow emission-line measurements, we have
identified 136 galaxies with photoionization signatures
of an active massive BH (Figure 1, Tables 1 and 2).
There are 35 galaxies with narrow-line ratios falling in
the AGN-dominated region of the BPT diagram and 101
galaxies with composite spectra. While we consider the
BPT-AGN more secure5 , the composite spectra likely indicate at least some contribution from an AGN (Trouille
et al. 2011; Jia et al. 2011), which for our purposes
is sufficient for tentatively identifying the presence of
a massive BH. Even with our inclusive approach, only
∼ 0.5% (136/25974) of dwarf emission-line galaxies in
our parent sample exhibit optical narrow-line signatures
of photoionization from an accreting BH (although see
the discussion in Section 5 for a number of caveats).
We also investigate the positions of AGNs and composite galaxies according to the [O III]/Hβ vs. [N II]/Hα diagram in two secondary diagnostic diagrams, [O III]/Hβ
vs. [S II]/Hα and [O III]/Hβ vs. [O I]/Hα (Figure 2).
[O I]/Hα is particularly useful as it is sensitive to the
hardness of the ionizing radiation field (e.g., Kewley et al.
5 The left-most red point in Figure 1 corresponds to a bright offnuclear source in a blue late-type irregular dwarf galaxy, that may
in fact be an extreme H II region. While we cannot exclude the
possibility that this source is a low-metallicity active massive BH,
we consider it rather suspect in the absence of other supporting
evidence.
8. 8
Reines et al.
2006), although [O I] is relatively weak and not detected
in ∼50% of the AGNs + composites (Table 2). Figure
2 shows that nearly all of the [N II]/Hα AGN fall in the
Seyfert region of the secondary diagnostic diagrams, with
at most 3 falling in the LINER part of the diagrams. The
[N II]/Hα composites fall throughout the [S II]/Hα and
[O I]/Hα diagrams.
The SDSS spectra of the BPT-AGN are shown in Figures 3 and 4 with the continuum and absorption line
models over-plotted in blue. Our sample of BPT-AGN
includes NGC 4395 and 2 galaxies from the low-mass
Seyfert 2 sample of Barth et al. (2008). The remaining
galaxies in Barth et al. (2008) do not meet the selection
criteria to be included in our parent dwarf galaxy sample (§2). Due to the large number of composites, we do
not show their spectra here. However, we have inspected
all of the individual spectra flagged as composites by eye
and cut sources with unreliable emission line measurements due to low signal-to-noise. Twenty objects were
excluded, leaving a final sample of 101 composites.
3.4. Broad-Line AGN Candidates
We also search for broad Hα emission in our parent
sample of galaxies, which may indicate dense gas orbiting a BH within the broad-line region (BLR), only
light-days from the central BH (e.g., Peterson et al. 2004,
2005; Bentz et al. 2009b). Unobscured quasars powered
by ∼ 108 M BHs have typical line-widths of ∼3000 km
s−1 (e.g., Shen et al. 2008). However, in AGNs with lowmass BHs (MBH 106.5 M ), the line-widths can be just
hundreds of km s−1 (e.g., Filippenko & Ho 2003; Greene
& Ho 2007a). While in principle broad emission lines
provide clear evidence that gas is moving in the potential of a compact massive object (e.g., Ho et al. 1997),
there are a few complications, particularly in this lowmass regime. First, Hα absorption from young stars can
mask or mimic the broad Hα, and thus accurate galaxy
continuum subtraction is required (Section 3.1; also see
Greene & Ho 2004). Second, some varieties of supernovae
(SNe) can masquerade as AGNs at low-luminosities (see
below).
Out of the 51 sources flagged as having a broad Hα
component in their spectra with a FWHM ≥ 500 km
s−1 (see §3.2), 25 make it into our final sample of broadline AGN candidates after a more careful examination of
each individual source. We detect broad Hβ, in addition
to broad Hα in 36% (9/25) of these sources (Tables 2
and 4). We have excluded 9 likely Type II SNe (most
having characteristic P Cygni profiles), 3 non-nuclear
star-forming knots in nearby galaxies (with low broad
Hα luminosities), 1 Luminous Blue Variable star identified by Izotov & Thuan (2009b, NSAID 5109), and 13
sources in the star-forming region of the BPT diagram
with marginal detections of broad Hα that are unconvincing by eye. Figure 5 shows the spectral fits for one
of our broad-line AGN candidates. Plots for the other
broad-line AGN candidates are shown in the Appendix.
Our broad-line sample includes NGC 4395, the dwarf
disk galaxy presented in Dong et al. (2007), and 4 galaxies from the samples of Greene & Ho (2007a) and Dong
et al. (2012). The remaining samples of low-mass BHs
in the latter two works are hosted in galaxies that do
not meet the selection criteria to be included in our
Figure 2. BPT narrow-line diagnostic diagrams for our sam-
ple of active galaxies. Regions are delineated according to the
classification scheme outlined in Kewley et al. (2006). Top:
[O III]/Hβ versus [N II]/Hα diagram. There are 35 galaxies
in the AGN part of the diagram (6 with broad Hα emission)
and 101 galaxies in the composite region of the diagram (4
with broad Hα emission). An additional 15 galaxies have
broad Hα emission, yet have HII-region-like narrow-line ratios. Middle: [O III]/Hβ versus [S II]/Hα diagram. Colors
indicate classification based on the OIII/Hβ versus [N II]/Hα
diagram. Bottom: [O III]/Hβ versus [O I]/Hα diagram for
galaxies in which we detect the [O I] emission line (Tables 2
and 4). Colors indicate classification based on the OIII/Hβ
versus [N II]/Hα diagram.
9. Dwarf Galaxies with Active Massive Black Holes
9
Figure 3. SDSS redshift-corrected spectra of galaxies falling in the AGN region of the [O III]/Hβ versus [N II]/Hα diagram. Continuum
and absorption-line fits are shown in blue (see Section 3.1). An identification number (Table 1) is given in the upper left corner of each
plot.
10. 10
Reines et al.
Figure 4. Same as Figure 3.
parent dwarf catalog (§2). The same is true of the
four candidate metal-poor AGN presented in Izotov &
Thuan (2008). Our broad-line sample also includes
HS 0837+4717 (source B), which has narrow-line ratios consistent with a low-metallicity starburst or a low-
metallicity AGN, and exhibits persistent broad emission
lines (Kniazev et al. 2000; Izotov et al. 2007).
For each of our broad-line candidates, we check if the
broad Hα component could be an artifact from oversubtracting the Hα absorption line. We fit a single Gaus-
11. Dwarf Galaxies with Active Massive Black Holes
11
Figure 5. Example of a broad-line AGN candidate (ID 119). The narrow-line ratios of this source place it in the composite section of
the [O III]/Hβ versus [N II]/Hα diagram. Top: The redshift-corrected spectrum with the continuum and absorption-line fit plotted in
blue. Bottom: Chunks of the emission-line spectrum (after continuum and absorption-line subtraction). Best-fitting models are plotted in
red and the individual narrow Gaussian components are plotted in yellow. The broad Hα and Hβ components are plotted in dark blue.
Residuals are plotted in gray with a vertical offset for clarity. Reduced χ2 values are shown in the upper left-hand corner of the Hα +
[N II] and Hβ chunks. For comparison, the reduced χ2 values from the fits not including a broad component are shown in parenthesis.
Spectra of the other 24 broad-line AGN candidates are shown in the Appendix.
sian to the Hα absorption line in the model fit (Section
3.1), measure the corresponding equivalent width (EW)
and FWHM, and compare these values to the broad Hα
emission component. As shown in Figure 6, the EWs
of the broad emission features are ∼ 3 to 36 times the
EWs of the absorption features and the FWHMs of the
broad Hα components are ∼ 2 to 11 times the FWHMs
of the absorption lines. Moreover, in all but 1 case, the
FWHMs of the Hα absorption lines are less than 500 km
s−1 , our minimum threshold for the width of any broad
Hα emission. Thus, our broad Hα detections appear to
be robust and not a result of over-subtracting an absorption feature.
Figure 6. Ratios of the EWs and FWHMs of the broad components of Hα emission to the Hα absorption lines for the broad-line
AGN candidates (Section 3.4). Points are color-coded according
to their position in the [O III]/Hβ versus [N II]/Hα BPT diagram.
Dashed lines indicate ratios equal to 1. This plot demonstrates that
the broad Hα emission features are not a result of over-subtracting
the Hα absorption features. Absorption lines were not detected in
4 of the 25 broad-line AGN candidates and they are excluded here.
The broad-line AGN candidates are found throughout the BPT diagrams (Figures 1 and 2), as is the case
for other samples of Type 1 AGN (Greene & Ho 2007a;
Stern & Laor 2013). Ten of the galaxies fall in either the
AGN or composite region of the [O III]/Hβ vs. [N II]/Hα
diagram and we consider these the most secure broadline AGN candidates, half of which are new identifications6 . Accounting for just the BPT-AGN, the fraction of sources with a detectable broad Hα component
(i.e., the Type 1 fraction) is ∼17% (6/35). The other 15
broad-line sources fall in the star-forming region of the
[O III]/Hβ vs. [N II]/Hα diagram (Tables 3 and 4), 2 of
which fall in the Seyfert (and 2 in the LINER) region of
the [O III]/Hβ vs. [O I]/Hα diagram. While models of
low-metallicity AGNs overlap with low-metallicity starbursts (Groves et al. 2006), only one of the broad-line
sources in the star-forming part of the [O III]/Hβ vs.
[N II]/Hα diagram also has narrow-line ratios consistent
with a low-metallicity AGN (source B). For the majority
of cases, the narrow-lines are likely dominated by star
formation. Bona fide broad-line AGN falling in the starforming part of the diagnostic diagram can naturally be
explained by star-formation dominating the narrow-line
emission within the 3 SDSS aperture, which can cover
a substantial fraction of the host galaxy for these dwarfs.
It is also possible, however, that the broad Hα seen in objects lying in the star-forming region of the BPT diagram
is in fact from stellar phenomena.
Broad Hα from galaxies in the star-forming region of
the BPT diagram may well be from luminous Type II
SNe that happened to be detectable when the SDSS spectra were taken and fell within the spectroscopic aperture. Type II SNe can exhibit broad Hα emission with
luminosities upwards of ∼ 1040 erg s−1 , which is comparable to the luminosities of our broad-line sources and
other examples of AGNs with low-mass BHs (Filippenko
& Ho 2003; Greene & Ho 2007a). Some Type II SNe
also exhibit broad P Cygni profiles in Hα and we have
already excluded these sources from our broad-line sam6 Barth et al. (2008) identify a tentative broad component in ID
32 (Table 1).
12. 12
Reines et al.
Table 3
BPT Star-Forming Galaxies with Broad Hα: Galaxy Properties
ID
(1)
NSAID
(2)
SDSS Name
(3)
Plate-MJD-Fiber
(4)
z
(5)
log M
(6)
Mg
(7)
g−r
(8)
r50
(9)
S´rsic n
e
(10)
Aa
Bb
C
D
E
F
G
H
I
Ja
K
L
M
N
O
22083
15952
109990
76788
109016
12793
13496
74914
112250
41331
91579
33207
119311
88972
104565
J004042.10−110957.7
J084029.91+470710.4
J090019.66+171736.9
J091122.24+615245.5
J101440.21+192448.9
J105100.64+655940.7
J105447.88+025652.4
J111548.27+150017.7
J112315.75+240205.1
J114343.77+550019.4
J120325.66+330846.1
J130724.64+523715.5
J131503.77+223522.7
J131603.91+292254.0
J134332.09+253157.7
655-52162-89
549-51981-621
2432-54052-524
1786-54450-514
2373-53768-148
490-51929-279
507-52353-619
1752-53379-532
2497-54154-221
1015-52734-596
2089-53498-283
887-52376-454
2651-54507-488
2009-53904-640
2246-53767-49
0.0274
0.0421
0.0288
0.0266
0.0289
0.0325
0.0222
0.0501
0.0250
0.0272
0.0349
0.0262
0.0230
0.0378
0.0287
9.45
8.11
9.30
8.79
8.75
9.11
8.90
8.82
9.01
9.01
9.01
9.09
9.14
8.93
9.35
−18.14
−18.89
−19.08
−18.56
−17.90
−19.05
−18.56
−18.93
−18.33
−17.97
−17.44
−19.14
−18.90
−19.72
−18.58
0.56
−0.85
0.26
0.26
0.23
0.11
0.20
0.19
0.44
0.22
0.92
0.19
0.29
−0.14
0.37
1.0
0.9
2.3
2.2
0.9
0.8
0.9
1.5
0.8
1.1
1.1
1.2
1.7
1.4
3.3
2.3
6.0
1.1
0.6
1.9
6.0
2.9
5.3
6.0
0.9
5.9
1.3
3.9
3.1
0.9
Note. — Col.(1): Identification assigned in this paper. Col.(2): NSA identification number. Col.(3): SDSS name. Col.(4): Plate-MJDFiber of analyzed spectra. Col.(5): Redshift. Col.(6): Log galaxy stellar mass in units of M . Col.(7): Absolute g-band magnitude. Col.(8):
g − r color. Col.(9): Petrosian 50% light radius in units of kpc. Col.(10): S´rsic index, n. All values are from the NSA and assume h = 0.73.
e
Magnitudes are K-corrected to rest-frame values using kcorrect v4 2 and corrected for foreground Galactic extinction.
a Galaxies in Greene & Ho (2007) and Dong et al. (2012)
b HS 0837+4717 (Izotov et al. 2007). The [O III]/Hβ and [N II]/Hα ratios for this source are also consistent with a low-metallicity AGN.
Table 4
BPT Star-Forming Galaxies with Broad Hα: Emission Line Fluxes
ID
(1)
(Hβ)n
(2)
(Hβ)b
(3)
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
42(5)
2287(47)
340(6)
180(6)
408(10)
917(79)
1058(19)
164(6)
576(14)
227(9)
183(5)
685(16)
495(11)
3524(44)
34(4)
···
195(20)
···
···
···
311(13)
···
···
···
80(18)
···
···
···
···
···
[O III]λ5007
(4)
[O I]λ6300
(5)
[N II]λ6548
(6)
52(6)
14521(202)
560(9)
450(10)
1218(24)
1241(39)
1782(167)
394(10)
664(15)
299(10)
330(6)
1405(26)
441(20)
14615(162)
27(4)
21(5)
46(4)
29(3)
16(4)
32(5)
38(5)
54(6)
28(5)
62(7)
17(5)
30(3)
63(7)
15(5)
302(16)
9(2)
9(1)
54(2)
53(1)
16(1)
44(1)
361(31)
237(4)
23(1)
215(4)
39(2)
39(1)
111(3)
154(4)
365(4)
8(1)
(Hα)n
(7)
(Hα)b
(8)
113(6)
8066(82)
1155(14)
571(9)
1348(20)
3764(323)
3567(45)
549(10)
2264(30)
1065(31)
655(9)
2174(31)
1690(22)
11905(129)
106(3)
218(17)
1292(23)
749(21)
251(26)
107(17)
582(28)
365(27)
183(22)
196(27)
648(22)
155(10)
236(35)
521(30)
907(55)
46(8)
[N II]λ6583
(9)
[S II]λ6716
(10)
[S II]λ6731
(11)
26(3)
161(5)
157(3)
48(3)
129(4)
1069(77)
702(12)
68(4)
638(12)
116(5)
114(3)
329(8)
457(10)
1080(13)
23(2)
44(4)
115(4)
190(4)
99(4)
170(6)
293(57)
518(11)
86(4)
392(10)
135(6)
133(4)
371(10)
229(7)
981(15)
36(3)
32(3)
107(3)
141(3)
66(3)
125(4)
263(89)
373(7)
64(3)
305(7)
90(4)
95(2)
288(7)
169(5)
727(10)
22(2)
Note. — Col.(1): Identification assigned in this paper. Col.(2)-(11): Emission line fluxes with units of 10−17 erg s−1 cm−2 . Errors are shown in parenthesis. No
extinction correction has been applied. The subscripts n and b refer to the narrow and broad components of the line, respectively. A three-dot ellipsis indicates that no
broad component of Hβ is detected.
ple. We identified 9 such objects by eye (Table 5), and
these were subsequently confirmed by the automated SNe
detection code used in Graur & Maoz (2013) (O.Graur,
private communication). Two objects, NSAID 119259
and NSAID 69982, have also been identified as Type II
SNe by Izotov & Thuan (2009a) and Izotov et al. (2007),
respectively. Figure 7 shows the spectral region around
Hα for the SNe candidates. In some cases, the P Cygni
profile is very subtle with only slight blue-shifted absorption indicated by an asymmetric emission line profile.
Another way we can identify SNe in our broad-line sample is to examine the temporal evolution of the broad Hα
emission. We would expect the broad line to persist for
an AGN, whereas it should significantly decrease or disappear over a timespan of several years for SNe. Therefore, we are currently obtaining follow-up spectroscopy
of the broad-line sources, the results of which will be
presented in a forthcoming paper.
We also consider stellar winds from evolving massive
stars undergoing mass loss, such as those from WolfRayet (WR) stars and Luminous Blue Variables (LBVs).
WR stars are identified in the integrated spectra of galaxies by the blended emission from helium, carbon and nitrogen at λ4650 − 4690 known as the “WR bump” and
this feature is only detected in four of our broad-line
AGN candidates by Brinchmann et al. (2008)7 . Two are
BPT-AGN, including NGC 4395 and one of the galaxies from the Barth et al. (2008) sample (IDs 21 and
32), and two are BPT-star-forming galaxies (IDs B and
F). We note that broad He II λ4686 can also be produced by AGN and thus the identifications of WR fea7 The work of Brinchmann et al. (2008) makes use of DR6,
whereas we use DR8. 18 of our 25 broad-line AGN candidates
are found in DR6.
13. Dwarf Galaxies with Active Massive Black Holes
13
Table 5
Supernova Candidates
NSAID
(1)
SDSS Name
(2)
Plate-MJD-Fiber
(3)
z
(4)
log M
(5)
Mg
(6)
12271
47648
61339
69671
69982a
75038
117522
119259b
160073
J093313.94+015858.7
J082449.94+293644.1
J131307.11+460554.3
J162244.78+323933.0
J164402.63+273405.4
J113913.54+150215.7
J103134.64+190407.1
J132053.66+215510.2
J113322.89+550420.0
475-51965-626
1207-52672-512
1459-53117-22
1684-53239-484
1690-53475-360
1755-53386-516
2593-54175-334
2651-54507-31
1014-52707-463
0.0311
0.0404
0.0296
0.0410
0.0232
0.0140
0.0342
0.0224
0.0091
8.94
9.45
9.46
9.41
8.93
8.51
8.89
8.55
8.65
−17.81
−19.06
−18.40
−19.74
−17.80
−17.08
−17.92
−16.97
−18.16
Note. — Col.(1): NSA identification number. Col.(2): SDSS name. Col(3): Plate-MJD-Fiber of
analyzed spectra. Col.(4): Redshift from NSA. Col.(5): Galaxy stellar mass from NSA corrected for
h = 0.73. Col.(6): Absolute g-band magnitude from NSA corrected for h = 0.73 and foreground
Galactic extinction.
a Possible Type IIp SNe identified by Izotov et al. (2007)
b Type IIn SNe identified by Izotov & Thuan (2009)
LBVs are sources of Balmer emission and can exhibit
broad Hα with velocities as large as ∼ 1500 km s−1 , yet
they are generally less luminous than Type II SNe (Smith
et al. 2011) and we therefore consider them a less likely
source of possible contamination in the broad-line sample. Nevertheless, like SNe, LBVs are transient events
that we can eliminate from our broad-line AGN candidates with our follow-up spectroscopic campaign.
In the spectra of some broad-line AGN candidates, the
broad Hα components are rather offset from the narrow
components. If a given broad Hα line is indeed from
gas orbiting a massive BH, this may suggest the AGN is
physically offset from the center of the galaxy (perhaps
due to a relatively shallow potential well in a low-mass
galaxy). Alternatively, the broad-line could be due to a
SNe offset from the galaxy center, which is more likely for
objects in the star-forming region of the BPT diagrams
with exceptionally broad Ha (e.g, object C). Our followup observations will help discern the origin of the offset
lines.
3.5. Black Hole Masses
Figure 7. The 9 supernovae candidates excluded from our broadline AGN candidates. The spectral region around Hα is shown with
the continuum and absorption line fits plotted in blue.
tures in these galaxies (especially the BPT-AGN) are suspect. Moreover, WR stars do not exhibit strong, if any,
hydrogen lines (e.g. Schaerer & Vacca 1998; Crowther
2007; Crowther & Walborn 2011). Therefore, we do not
consider WR stars a likely possibility for producing the
observed broad Hα in the broad-line AGN candidates.
For the objects with broad Hα emission, we can estimate indirect BH masses using scaling relations. If the
BLR gas is virialized, for which there is some evidence
(Peterson et al. 2004), then we can use the BLR kinematics as a dynamical tracer of the BH mass (MBH ∝
R∆V 2 /G). The average gas velocity is inferred from the
emission-line width. The BLR size has been measured
only for ∼ 50 active galaxies using reverberation mapping (e.g., Peterson et al. 2004; Bentz et al. 2009b; Denney et al. 2010; Barth et al. 2011; Bentz et al. 2013), in
which the time lag between continuum and BLR variability establishes a size scale for the BLR. In general, the
geometry of the BLR (and the proportionality constant)
is not known, and so the virial product alone (R∆V 2 /G)
does not establish the absolute BH mass. Instead, the ensemble of reverberation-based BH masses are calibrated
using the MBH − σ relation (Gebhardt et al. 2000b; Ferrarese et al. 2001; Nelson et al. 2004; Onken et al. 2004;
Greene & Ho 2006; Park et al. 2012; Grier et al. 2013),
although for some caveats see Greene et al. (2010).
For all other broad-line AGNs, the BLR size is unknown, and is indirectly estimated using a correlation
between AGN luminosity and BLR size (the radius-
14. 14
Reines et al.
luminosity relation) that is measured using Hβ timelag measurements from the reverberation-mapped sample (e.g., Kaspi et al. 2005; Bentz et al. 2009a, 2013).
Since the AGN continuum luminosity is virtually impossible to measure in these low-luminosity galaxies with
ongoing star formation, we use the broad Balmer line luminosity as a proxy for the AGN luminosity (e.g., Yee
1980).
We follow the approach outlined in Greene & Ho
(2005b) to estimate virial BH masses using the FWHM
and luminosity of broad Hα, but with the modified
radius-luminosity relationship of Bentz et al. (2013). Using the results from the “clean” fit in Bentz et al. (2013),
the RBLR − L relationship is given by
log
RBLR
lt − days
L5100
erg s−1
= 1.555 + 0.542 log
1044
.
(1)
Greene & Ho (2005b) present well-defined empirical correlations between broad Hα luminosity and continuum
luminosity, L5100 , and the line-widths (FWHM) of Hα
and Hβ:
LHα = 5.25 × 1042
L5100
1044 erg s−1
FWHMHβ = 1.07 × 103
1.157
FWHMHα
103 km s−1
erg s−1
(2)
km s−1 . (3)
RBLR FWHMHβ 2
G
,
(4)
gives
log
MBH
M
ID
(1)
1
9
11
20
21
32
48
119
123
127
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
log L(Hα)b
(2)
FWHM(Hα)b
(3)
BPT AGNs
39.38
1577
40.15
703
39.41
636
40.13
1526
38.15
1288
39.73
747
BPT Composites
39.67
894
40.16
1043
39.82
634
39.45
792
BPT Star-Forming
39.52
1782
40.67
1245
40.10
3690
39.56
4124
39.26
935
40.09
598
39.56
2027
39.97
3014
39.39
994
39.99
1521
39.58
774
39.51
3126
39.75
3563
40.42
645
38.88
1563
log MBH
(4)
5.7
5.4
4.9
6.1
5.0
5.2
5.4
5.7
5.1
5.2
5.9
6.1
6.8
6.7
5.2
5.2
6.1
6.6
5.3
6.0
5.2
6.4
6.6
5.4
5.5
1.03
Inserting the previous three equations into the virial relationship:
MBH =
Table 6
Broad-line AGN Candidates: BH Masses
LHα
(5)
1042 erg s−1
FWHMHα
.
+2.06 log
103 km s−1
= log + 6.57 + 0.47 log
Several values of the scale factor, , are found in the
literature8 , spanning a range of ∼ 0.75 − 1.4 (e.g., Onken
et al. 2004; Greene & Ho 2007a; Grier et al. 2013). Here
we assume = 1.
Table 6 lists the broad Hα luminosities, widths, and
virial BH masses for our sample of broad-line AGN candidates. The most secure broad-line AGN candidates (i.e.
those that lie in the AGN or composite region of the BPT
diagram) have broad Hα luminosities of ∼ 1039 − 1040
erg s−1 , with the exception of the nearby dwarf Seyfert
NGC 4395 that has a broad Hα luminosity of ∼ 1038
erg s−1 . For these sources, the widths (FWHM) of the
broad Hα components span a range of ∼ 600 − 1600
km s−1 . The virial BH masses calculated using Equation 6 are in the range ∼ 105 − 106 with a median of
8 We follow Onken et al. (2004) and denote the scale factor as
when using the FWHM of the line, as opposed to f when using
the second moment of the line profile, σ.
Note. — Col.(1): Identification assigned in this paper.
Col.(2): Luminosity of the broad component of Hα in units
of erg s−1 . Col.(3): FWHM of the broad component of
Hα, corrected for instrumental resolution, in units of km
s−1 . Col.(4): Virial mass estimate of the BH in units of
M , assuming the broad Hα emission is due to accretion.
As described in the text, the origin of the broad emission
for the BPT star-forming galaxies is unclear at present.
∼ 2×105 M . For comparison, the median BH masses in
the Greene & Ho (2007a) and Dong et al. (2012) samples
are ∼ 1 × 106 M . The less secure broad-line sources (in
the star-forming region of the BPT diagram) have broad
Hα luminosities comparable to the more secure broadline AGN candidates. However, the widths reach values
of a few thousand km s−1 , leading to anomalously large
BH mass estimates and possibly indicating a different
origin for the broad Hα emission at least in the most
extreme cases (Figure 8a, also see Section 3.4).
The virial BH mass measurements for the broad-line
AGN candidates are obviously extremely indirect, and
are subject to a number of systematic uncertainties. For
one thing, the BLR geometry clearly varies considerably
from object to object (Kollatschny 2003; Bentz et al.
2009b; Denney et al. 2010; Barth et al. 2011), making
a single geometric scaling factor suspect. Whether the
geometry depends on fundamental parameters of the BH
remains uncertain (Collin et al. 2006). Then there is
the danger that we are not measuring the velocities at
the same radius as probed with reverberation mapping
(Krolik 2001). At present, there simply are not enough
measurements to search for such systematics directly,
although progress with velocity-resolved reverberation
mapping is promising (Gaskell 1988; Kollatschny 2003;
Bentz et al. 2008; Denney et al. 2009; Barth et al. 2011).
Finally, reverberation mapping has been achieved in only
a few low-mass AGNs (Peterson et al. 2005; Rafter et al.
2011) and we therefore strongly caution that the BH
15. Dwarf Galaxies with Active Massive Black Holes
masses presented here are based on an extrapolation from
more luminous AGNs powered by more massive BHs and
living in very different environments.
3.6. Broad Hα Detection Limits
For the BPT AGN and composites that do not have
detectable broad Hα emission in their spectra, we determine upper limits on any potential broad Hα flux. We
add fake broad Hα components represented by Gaussians
to the emission-line spectra and measure the emission
lines with the code described in Section 3.2. The input
FWHM is held fixed at 500 km s−1 to match our selection criteria and we incrementally increase the height of
the Gaussian until our code flags the source as having a
broad Hα component. The minimum detectable flux is
∼ 10−15 erg s−1 cm−2 within a factor of ∼3 for nearly all
of the sources. This corresponds to a broad Hα luminosity of ∼ 2 × 1039 erg s−1 at a median redshift of z ∼ 0.03.
We note that all of the BPT AGN and composites with
detected broad Hα are above this threshhold, with the
exception of NGC 4395 that is only ∼4 Mpc away.
We estimate the bolometric luminosity of an AGN
corresponding to our minimum detectable broad Hα
luminosity using the conversion between L(Hα) and
L(5100˚) in Equation 2 (Greene & Ho 2005b) and
A
Lbol = 10.3L(5100˚) (Richards et al. 2006). We caution
A
that these relationships come from studies of more luminous Seyfert 1 galaxies and quasars. Nevertheless, we use
these relationships and estimate that an AGN must have
a minimum bolometric luminosity of Lbol 1042 erg s−1
for us to detect broad Hα emission (modulo obscuration
from dust).
In principle, we could detect broad Hα from a BH with
a mass as low as ∼ 8 × 103 M if it was accreting at its
Eddington limit, where LEdd = 1.3 × 1038 (MBH /M )
erg s−1 . Since maximally accreting BHs are very rare
(Schulze & Wisotzki 2010), it is not surprising that we do
not detect such low-mass BHs (if they exist) in the limited volume of our sample (z < 0.055). In other words,
we cannot rule out the existence of ∼ 104 M BHs. We
just cannot detect them via broad Hα if they are radiating much below their Eddington luminosity. A 105 M
BH, on the other hand, only needs to be radiating at
∼8% of its Eddington luminosity to produce detectable
broad Hα within our survey volume.
4. HOST GALAXIES
The NSA, from which we have drawn our parent sample of dwarfs (Section 2), provides a number of galaxy
parameters. In Figure 8b–f, we plot the distributions of
various properties for the 136 galaxies that exhibit ionization signatures of BH accretion in their spectra (i.e.,
those galaxies with narrow-line ratios falling in the AGN
and composite region of the BPT diagram). We do not
include the 15 broad-line AGN candidates falling in the
star-forming region of the BPT diagram for the reasons
discussed in Section 3.4. For comparison, we also show
the distributions for our parent sample of emission-line
galaxies normalized to the same number sources (136),
as well as the 35 BPT-AGNs alone.
By design, the galaxies in our sample have stellar
masses M
3 × 109 M , which is approximately the
stellar mass of the LMC (van der Marel et al. 2002).
15
While active BHs are preferentially found in more massive galaxies within our parent sample, we do detect
active BHs in galaxies 10 times less massive than our
threshold with stellar masses comparable to the Small
Magellanic Cloud (SMC, M ∼ 3×108 M ; Stanimirovi´
c
et al. 2004). Stellar masses in the NSA are derived from
kcorrect (Blanton & Roweis 2007) using Galaxy Evolution Explorer (GALEX) UV and SDSS ugriz bands
combined, and while they do not account for any possible AGN contribution, we do not expect the active BHs
in our sample to significantly impact stellar mass estimates of the host galaxies. The use of many broadband
filters should help mitigate the contribution from strong
emission lines, and the vast majority of sources are type 2
AGN that are known to contribute very little continuum
emission (e.g., Schmitt et al. 1999). For the small fraction
of type 1 AGN candidates, the host galaxy stellar masses
could in principle be artificially elevated by a boost in
flux from the AGN continuum. However, HST I-band
imaging of two of our broad-line AGN candidates (IDs
20 and 123; Jiang et al. 2011) that are also in the sample
of low-mass BHs presented by Greene & Ho (2007a) reveals that the AGNs in these galaxies contribute 10%
of the total flux.
The active galaxies in our sample have a total (host
+ AGN) median absolute g-band magnitude of Mg =
LMC
∼
−18.1 mag, which is comparable to the LMC (Mg
−18.2 mag; Tollerud et al. 2011) and ∼1–2 magnitudes
fainter than previous samples of low-mass AGN. Correcting the median absolute magnitudes to our adopted cosmology (h = 0.73), the Barth et al. (2008) sample of lowmass Seyfert 2 galaxies has Mg = −19.0, and the lowmass Seyfert 1 samples of Greene & Ho (2007a) and Dong
et al. (2012) have Mg = −19.4 mag and Mg = −20.3
mag, respectively, after removing the AGN contribution.
The colors of our sample of dwarfs hosting active BHs
tend to be redder compared to our parent sample of
dwarfs. The distribution of colors remains essentially the
same for the parent sample even when applying a mass
cut of log M > 9.25, and therefore the color difference
between the active sample and parent sample is not a
mass effect. The AV ’s of the active galaxies derived from
our continuum and absorption line fits are similar to the
parent sample (∼0 to 1 with a median of ∼ 0.3), suggesting the redder colors are not due to differences in dust
properties. More likely, the color difference is a selection effect such that the optical diagnostics we are using
are not sensitive to accreting BHs in blue galaxies with
ongoing star-formation that dominates the emission-line
spectra.
In addition to being low-mass, the active galaxies in
our sample are physically small, with typical half-light
radii r50
2 kpc. The distribution of BPT-AGN and
composites is skewed towards smaller sizes relative to
our parent sample of dwarf galaxies. A similar trend
is seen in the distribution of 90%-light radii, suggesting
the galaxies hosting active BHs are indeed preferentially
compact and this result is not due to the presence of a
bright central point source.
Single-component two-dimensional S´rsic fits are also
e
provided in the NSA and the galaxies in our sample span
a large range of S´rsic index, n. Relative to our parent
e
sample, a larger fraction of the active galaxies have high-
16. 16
Reines et al.
Figure 8. Panel a): Virial BH mass distribution for broad-line AGN candidates. BPT AGNs and composites are shown in orange. BPT
star-forming galaxies, for which the origin of the broad-line emission is somewhat ambiguous, are shown in blue. Panels b–f ): Distributions
of host galaxy properties provided in the NSA for the 136 galaxies with narrow-line ionization signatures of BH accretion. BPT AGNs and
composites are shown in the orange hashed histograms, and the distributions of BPT-AGNs only are shown in red. Our parent sample of
dwarf emission-line galaxies is shown in black, normalized to the number of galaxies in the orange histogram (136 BPT AGN + composites).
We show the distributions of galaxy stellar masses (with stellar masses of the Magellanic Clouds indicated in blue), total absolute g-band
magnitude, g − r color, Petrosian 50% light radius, and S´rsic index. All magnitudes are K-corrected to rest-frame values using kcorrect
e
v4 2 and corrected for foreground Galactic extinction. NSA values have been modified assuming h = 0.73.
n values, although BHs are also found in low-n disky
galaxies. Figure 9 shows the SDSS images of a selection
of galaxies in our sample with BH accretion signatures.
5. DEMOGRAPHICS
The fraction of optically-selected, active BHs in our
parent sample of dwarf galaxies is ∼0.5% (136/25974)9 .
However, there are a number of obstacles preventing us
from determining the true occupation fraction and BH
mass function in this low-mass regime. First of all, our
optical diagnostics are only sensitive to actively accreting BHs, and even at their Eddington limit low-mass BHs
are relatively faint. Furthermore, small galaxies generally have ongoing star formation, gas, and dust that can
mask or extinguish the optical signatures of BH accretion. Therefore, while there may an accreting BH present
9 Including the additional 15 broad-line AGN candidates in the
star-forming region of the BPT diagram does not have a significant
impact on the active fraction, increasing it to ∼0.6%.
at the center of a galaxy, the total observed line emission
in the SDSS aperture may be dominated by star formation. Indeed, the SDSS aperture of 3 is comparable to
the median half-light radius of our dwarf galaxy sample. Even without significant ongoing star formation,
AGN signatures may be heavily diluted by host galaxy
light such that the emission lines are effectively hidden
(Moran et al. 2002). Additionally, low-metallicty AGN,
which may be expected in lower-mass galaxies, can fall
(and hide) in the upper left region of the star-forming
plume of galaxies in the [O III]/Hβ versus [N II]/Hα diagnostic diagram (Groves et al. 2006). Therefore, while
we can identify bona-fide AGNs based on their location in
the BPT diagram, the selection of massive BHs is likely
highly incomplete. Even if we understand our incompleteness from these effects, to derive a true space density requires that we know the distribution of Eddington
ratios in these low-mass systems as compared to more
massive galaxies (e.g., Heckman et al. 2004; Gallo et al.
17. Dwarf Galaxies with Active Massive Black Holes
17
Figure 9. A selection of galaxies from our sample of dwarfs hosting active massive BHs. The SDSS color composite images have a size
of 50 × 50 . The identification numbers assigned in this work are in the upper left corners of the images, with the SDSS name below.
2010; Aird et al. 2012) where we believe the occupation
fraction is close to unity. It is interesting to note, however, that our active fraction is quite similar to that of
∼ 107 M BHs radiating at ∼10% of their Eddington
limit (Heckman et al. 2004; Greene & Ho 2007b).
Using broad emission lines to identify AGN in dwarf
galaxies poses a different set of problems. The broadline signature is weaker for low-mass BHs and can be
difficult to detect in galaxy-dominated spectra. There is
also the possibility that the broad-line region disappears
altogether below some critical luminosity or Eddington
ratio (e.g., Nicastro 2000; Laor 2003; Elitzur & Ho 2009;
Trump et al. 2011; Marinucci et al. 2012). There are
a number of candidate “true” Type 2 AGNs (e.g., Tran
2003; Bianchi et al. 2008) that show no sign of a broadline region in direct or polarized light, and no clear signs
of obscuration in X-rays. It is thus possible that the
Type 1 fraction drops towards lower luminosity, which
could add significant complications in attempting to use
these AGN as a tracer of the demographics of BHs in
dwarf galaxies.
6. CONCLUSIONS
Using optical spectroscopy from the SDSS, we have
systematically assembled the largest sample of dwarf
galaxies (108.5
M
109.5 M ) hosting massive BHs
to date. These dwarf galaxies have stellar masses comparable to the Magellanic Clouds and contain some of
the least-massive supermassive BHs known. Contrary to
common lore, low-mass, physically small dwarf galaxies
can indeed form massive BHs.
We find photoionization signatures of BH accretion
in 136 galaxies using the narrow-line [O III]/Hβ versus [N II]/Hα diagram as our primary diagnostic. Of
these, 35 have AGN-dominated spectra and 101 have
composite spectra suggesting ionization from both an
AGN and massive stars. For the small fraction of these
active galaxies with detectable broad Hα emission, we
estimate a median virial BH mass of MBH ∼ 2 × 105 M .
Our sensitivity to broad Hα emission limits our ability
to detect broad-line AGN with BH masses much below
∼ 105 M radiating at less than ∼10% of their Eddington luminosity. We find broad Hα in an additional 15
galaxies, yet their spectra exhibit narrow-line ratios consistent with star-forming galaxies. We caution that at
these low-luminosities and low-metallicities, particularly
for galaxies with high star formation rates, we are susceptible to contamination from stellar processes.
Ultimately, we need a complete census of massive
BHs in dwarf galaxies to place stringent constraints on
theories for the formation of supermassive BH seeds.
While optical diagnostics certainly have a role to play,
we need to move towards using alternative search techniques and observations at other wavelengths to make
further progress (e.g., radio and X-ray; Reines et al. 2011;
Reines & Deller 2012; Gallo et al. 2010; Miller et al. 2012;
Kamizasa et al. 2012).
We are grateful to the entire SDSS collaboration for
providing the data that made this work possible, to
Michael Blanton and all those involved in creating the
NASA-Sloan Atlas, and to Craig Markwardt for making
his MPFIT code publicly available. We thank the referee for a very helpful review that improved the paper.
A.E.R. appreciates helpful discussions with Mark Whittle, Jong-Hak Woo and Marta Volonteri. Support for
A.E.R. was provided by NASA through the Einstein Fellowship Program, grant PF1-120086. J.E.G. is partially
supported by an Alfred P. Sloan fellowship.
23. Dwarf Galaxies with Active Massive Black Holes
Figure 15. Same as Figure 5.
23
24. 24
Reines et al.
REFERENCES
Aihara, H., Allende Prieto, C., An, D., et al. 2011, ApJS, 193, 29
Aird, J., Coil, A. L., Moustakas, J., et al. 2012, ApJ, 746, 90
Alexandroff, R., et al. 2012, MNRAS, 423, 1325
Anders, P., & Fritze-v. Alvensleben, U. 2003, A&A, 401, 1063
Baldwin, J. A., Phillips, M. M., & Terlevich, R. 1981, PASP, 93, 5
Barth, A. J., Greene, J. E., & Ho, L. C. 2008, AJ, 136, 1179
Barth, A. J., Ho, L. C., Rutledge, R. E., & Sargent, W. L. W. 2004, ApJ, 607, 90
Barth, A. J., Strigari, L. E., Bentz, M. C., Greene, J. E., & Ho, L. C. 2009, ApJ, 690, 1031
Barth, A. J., Pancoast, A., Thorman, S. J., et al. 2011, ApJ, 743, L4
Begelman, M. C., Volonteri, M., & Rees, M. J. 2006, MNRAS, 370, 289
Bell, E. F., McIntosh, D. H., Katz, N., & Weinberg, M. D. 2003, ApJS, 149, 289
Bellovary, J., Volonteri, M., Governato, F., et al. 2011, ApJ, 742, 13
Bentz, M. C., Peterson, B. M., Netzer, H., Pogge, R. W., & Vestergaard, M. 2009a, ApJ, 697, 160
Bentz, M. C., et al. 2008, ApJ, 689, L21
—. 2009b, ApJ, 705, 199
Bentz, M. C., Denney, K. D., Grier, C. J., et al. 2013, ApJ, 767, 149
Bianchi, S., Corral, A., Panessa, F., et al. 2008, MNRAS, 385, 195
Blanton, M. R., Kazin, E., Muna, D., Weaver, B. A., & Price-Whelan, A. 2011, AJ, 142, 31
Blanton, M. R., & Roweis, S. 2007, AJ, 133, 734
Brinchmann, J., Kunth, D., & Durret, F. 2008, A&A, 485, 657
Bromm, V., & Yoshida, N. 2011, ARA&A, 49, 373
Bruzual, G., & Charlot, S. 2003, MNRAS, 344, 1000
Cardelli, J. A., Clayton, G. C., & Mathis, J. S. 1989, ApJ, 345, 245
Collin, S., Kawaguchi, T., Peterson, B. M., & Vestergaard, M. 2006, A&A, 456, 75
Croton, D. J., Springel, V., White, S. D. M., et al. 2006, MNRAS, 365, 11
Crowther, P. A. 2007, ARA&A, 45, 177
Crowther, P. A., & Walborn, N. R. 2011, MNRAS, 416, 1311
Denney, K. D., Peterson, B. M., Pogge, R. W., et al. 2009, ApJ, 704, L80
—. 2010, ApJ, 721, 715
Desroches, L.-B., & Ho, L. C. 2009, ApJ, 690, 267
Dong, X., Wang, T., Yuan, W., et al. 2007, ApJ, 657, 700
Dong, X.-B., Ho, L. C., Yuan, W., et al. 2012, ApJ, 755, 167
Dressler, A., & Richstone, D. O. 1988, ApJ, 324, 701
Elitzur, M., & Ho, L. C. 2009, ApJ, 701, L91
Eracleous, M., Hwang, J. A., & Flohic, H. M. L. G. 2010, ApJ, 711, 796
Fan, X., et al. 2001, AJ, 122, 2833
Ferrarese, L., & Merritt, D. 2000, ApJ, 539, L9
Ferrarese, L., Pogge, R. W., Peterson, B. M., et al. 2001, ApJ, 555, L79
Filippenko, A. V., & Ho, L. C. 2003, ApJ, 588, L13
Filippenko, A. V., & Sargent, W. L. W. 1988, ApJ, 324, 134
—. 1989, ApJ, 342, L11
Gallo, E., Treu, T., Jacob, J., et al. 2008, ApJ, 680, 154
Gallo, E., Treu, T., Marshall, P. J., et al. 2010, ApJ, 714, 25
Gaskell, C. M. 1988, ApJ, 325, 114
Gebhardt, K., et al. 2000a, ApJ, 539, L13
—. 2000b, ApJ, 543, L5
—. 2001, AJ, 122, 2469
Geha, M., Blanton, M. R., Yan, R., & Tinker, J. L. 2012, ApJ, 757, 85
Ghosh, H., Mathur, S., Fiore, F., & Ferrarese, L. 2008, ApJ, 687, 216
Goulding, A. D., Alexander, D. M., Lehmer, B. D., & Mullaney, J. R. 2010, MNRAS, 406, 597
Graur, O., & Maoz, D. 2013, MNRAS, 430, 1746
Greene, J. E. 2012, Nature Communications, 3, arXiv:1211.7082
Greene, J. E., & Ho, L. C. 2004, ApJ, 610, 722
—. 2005a, ApJ, 627, 721
—. 2005b, ApJ, 630, 122
—. 2006, ApJ, 641, L21
—. 2007a, ApJ, 670, 92
—. 2007b, ApJ, 667, 131
Greene, J. E., Ho, L. C., & Barth, A. J. 2008, ApJ, 688, 159
Greene, J. E., et al. 2010, ApJ, 721, 26
Grier, C. J., Martini, P., Watson, L. C., et al. 2013, ArXiv e-prints, arXiv:1305.2447
Groves, B. A., Heckman, T. M., & Kauffmann, G. 2006, MNRAS, 371, 1559
G¨ltekin, K., Richstone, D. O., Gebhardt, K., et al. 2009, ApJ, 698, 198
u
Gunn, J. E., Siegmund, W. A., Mannery, E. J., et al. 2006, AJ, 131, 2332
Haehnelt, M. G., & Rees, M. J. 1993, MNRAS, 263, 168
Hao, L., Strauss, M. A., Tremonti, C. A., et al. 2005, AJ, 129, 1783
Heckman, T. M. 1980, A&A, 87, 152
Heckman, T. M., Kauffmann, G., Brinchmann, J., et al. 2004, ApJ, 613, 109
Heckman, T. M., Miley, G. K., van Breugel, W. J. M., & Butcher, H. R. 1981, ApJ, 247, 403
Ho, L. C. 2008, ARA&A, 46, 475
Ho, L. C., Filippenko, A. V., Sargent, W. L. W., & Peng, C. Y. 1997, ApJS, 112, 391
Hughes, S. A. 2002, MNRAS, 331, 805
Izotov, Y. I., & Thuan, T. X. 2008, ApJ, 687, 133
—. 2009a, ApJ, 707, 1560
25. Dwarf Galaxies with Active Massive Black Holes
—. 2009b, ApJ, 690, 1797
Izotov, Y. I., Thuan, T. X., & Guseva, N. G. 2007, ApJ, 671, 1297
Jardel, J. R., & Gebhardt, K. 2012, ApJ, 746, 89
Jia, J., Ptak, A., Heckman, T. M., et al. 2011, ApJ, 731, 55
Jiang, Y.-F., Greene, J. E., Ho, L. C., Xiao, T., & Barth, A. J. 2011, ApJ, 742, 68
Kamizasa, N., Terashima, Y., & Awaki, H. 2012, ApJ, 751, 39
Kaspi, S., Maoz, D., Netzer, H., et al. 2005, ApJ, 629, 61
Kauffmann, G., et al. 2003a, MNRAS, 341, 54
—. 2003b, MNRAS, 346, 1055
Kewley, L. J., Dopita, M. A., Sutherland, R. S., Heisler, C. A., & Trevena, J. 2001, ApJ, 556, 121
Kewley, L. J., Groves, B., Kauffmann, G., & Heckman, T. 2006, MNRAS, 372, 961
Kimm, T., Somerville, R. S., Yi, S. K., et al. 2009, MNRAS, 394, 1131
Kniazev, A. Y., Pustilnik, S. A., Ugryumov, A. V., & Kniazeva, T. F. 2000, Astronomy Letters, 26, 129
Kollatschny, W. 2003, A&A, 407, 461
Kormendy, J. 2004, in in Coevolution of Black Holes and Galaxies (Cambridge: Cambridge University Press), ed. L. C. Ho, 169
Kormendy, J., & Ho, L. C. 2013, ArXiv e-prints, arXiv:1304.7762
Kormendy, J., & Richstone, D. 1995, ARA&A, 33, 581
Krolik, J. H. 2001, ApJ, 551, 72
Kunth, D., Sargent, W. L. W., & Bothun, G. D. 1987, AJ, 93, 29
Laor, A. 2003, ApJ, 590, 86
Liu, X., Shapley, A. E., Coil, A. L., Brinchmann, J., & Ma, C.-P. 2008, ApJ, 678, 758
Lodato, G., & Natarajan, P. 2006, MNRAS, 371, 1813
Lora, V., S´nchez-Salcedo, F. J., Raga, A. C., & Esquivel, A. 2009, ApJ, 699, L113
a
Ludwig, R. R., Greene, J. E., Barth, A. J., & Ho, L. C. 2012, ApJ, 756, 51
Marconi, A., & Hunt, L. K. 2003, ApJ, 589, L21
Marinucci, A., Bianchi, S., Nicastro, F., Matt, G., & Goulding, A. D. 2012, ApJ, 748, 130
Markwardt, C. B. 2009, in Astronomical Society of the Pacific Conference Series, Vol. 411, Astronomical Data Analysis Software and
Systems XVIII, ed. D. A. Bohlender, D. Durand, & P. Dowler, 251
Mateo, M. L. 1998, ARA&A, 36, 435
McConnachie, A. W. 2012, AJ, 144, 4
McConnell, N. J., & Ma, C.-P. 2013, ApJ, 764, 184
Merloni, A., Heinz, S., & di Matteo, T. 2003, MNRAS, 345, 1057
Miller, B., Gallo, E., Treu, T., & Woo, J.-H. 2012, ApJ, 747, 57
M¨
ıller, J. M., & G¨ltekin, K. 2011, ApJ, 738, L13
u
Miller, M. C., & Davies, M. B. 2012, ApJ, 755, 81
Milosavljevi´, M., Bromm, V., Couch, S. M., & Oh, S. P. 2009, ApJ, 698, 766
c
Moran, E. C., Eracleous, M., Leighly, K. M., et al. 2005, AJ, 129, 2108
Moran, E. C., Filippenko, A. V., & Chornock, R. 2002, ApJ, 579, L71
Mortlock, D. J., Warren, S. J., Venemans, B. P., et al. 2011, Nature, 474, 616
Moustakas, J., Kennicutt, Jr., R. C., & Tremonti, C. A. 2006, ApJ, 642, 775
Nelson, C. H., Green, R. F., Bower, G., Gebhardt, K., & Weistrop, D. 2004, ApJ, 615, 652
Neumayer, N., & Walcher, C. J. 2012, Advances in Astronomy, 2012, arXiv:1201.4950
Nicastro, F. 2000, ApJ, 530, L65
Onken, C. A., Ferrarese, L., Merritt, D., et al. 2004, ApJ, 615, 645
Panessa, F., Wolter, A., Pellegrini, S., et al. 2005, ApJ, 631, 707
Park, D., Woo, J.-H., Treu, T., et al. 2012, ApJ, 747, 30
Peterson, B. M., et al. 2004, ApJ, 613, 682
—. 2005, ApJ, 632, 799
Portegies Zwart, S. F., Baumgardt, H., Hut, P., Makino, J., & McMillan, S. L. W. 2004, Nature, 428, 724
Rafter, S. E., Kaspi, S., Behar, E., Kollatschny, W., & Zetzl, M. 2011, ApJ, 741, 66
Reines, A. E., & Deller, A. T. 2012, ApJ, 750, L24
Reines, A. E., Nidever, D. L., Whelan, D. G., & Johnson, K. E. 2010, ApJ, 708, 26
Reines, A. E., Sivakoff, G. R., Johnson, K. E., & Brogan, C. L. 2011, Nature, 470, 66
Richards, G. T., et al. 2006, ApJS, 166, 470
Rosswog, S., Ramirez-Ruiz, E., & Hix, W. R. 2009, ApJ, 695, 404
Sarzi, M., et al. 2006, MNRAS, 366, 1151
Satyapal, S., B¨ker, T., Mcalpine, W., et al. 2009, ApJ, 704, 439
o
Satyapal, S., Vega, D., Dudik, R. P., Abel, N. P., & Heckman, T. 2008, ApJ, 677, 926
Satyapal, S., Vega, D., Heckman, T., O’Halloran, B., & Dudik, R. 2007, ApJ, 663, L9
Schaerer, D., & Vacca, W. D. 1998, ApJ, 497, 618
Schmitt, H. R., Storchi-Bergmann, T., & Fernandes, R. C. 1999, MNRAS, 303, 173
Schramm, M., Silverman, J. D., Greene, J. E., et al. 2013, ArXiv e-prints, arXiv:1305.3826
Schulze, A., & Wisotzki, L. 2010, A&A, accepted (astroph/1004.2671), arXiv:1004.2671
Seth, A. C., et al. 2010, ApJ, 714, 713
Shen, Y., Greene, J. E., Strauss, M. A., Richards, G. T., & Schneider, D. P. 2008, ApJ, 680, 169
Smith, N., Li, W., Silverman, J. M., Ganeshalingam, M., & Filippenko, A. V. 2011, MNRAS, 415, 773
Stanimirovi´, S., Staveley-Smith, L., & Jones, P. A. 2004, ApJ, 604, 176
c
Stern, J., & Laor, A. 2013, MNRAS, 431, 836
Strubbe, L. E., & Quataert, E. 2009, MNRAS, 400, 2070
Thornton, C. E., Barth, A. J., Ho, L. C., Rutledge, R. E., & Greene, J. E. 2008, ApJ, 686, 892
Tollerud, E. J., Boylan-Kolchin, M., Barton, E. J., Bullock, J. S., & Trinh, C. Q. 2011, ApJ, 738, 102
Tran, H. D. 2003, ApJ, 583, 632
Tremonti, C. A., Heckman, T. M., Kauffmann, G., et al. 2004, ApJ, 613, 898
Trouille, L., Barger, A. J., & Tremonti, C. 2011, ApJ, 742, 46
Trump, J. R., Impey, C. D., Kelly, B. C., et al. 2011, ApJ, 733, 60
Valluri, M., Ferrarese, L., Merritt, D., & Joseph, C. L. 2005, ApJ, 628, 137
van der Marel, R. P., Alves, D. R., Hardy, E., & Suntzeff, N. B. 2002, AJ, 124, 2639
25
26. 26
Reines et al.
van der Marel, R. P., Cretton, N., de Zeeuw, P. T., & Rix, H.-W. 1998, ApJ, 493, 613
Vaughan, S., Iwasawa, K., Fabian, A. C., & Hayashida, K. 2005, MNRAS, 356, 524
Veilleux, S., & Osterbrock, D. E. 1987, ApJS, 63, 295
Volonteri, M. 2010, A&A Rev., 18, 279
Volonteri, M., Lodato, G., & Natarajan, P. 2008, MNRAS, 383, 1079
Volonteri, M., & Natarajan, P. 2009, MNRAS, 400, 1911
Wetzel, A. R., Tinker, J. L., & Conroy, C. 2012, MNRAS, 424, 232
Whittle, M. 1985, MNRAS, 213, 1
Wrobel, J. M., & Ho, L. C. 2006, ApJ, 646, L95
Xue, Y. Q., Wang, S. X., Brandt, W. N., et al. 2012, ApJ, 758, 129
Yan, R. 2011, AJ, 142, 153
Yan, R., & Blanton, M. R. 2012, ApJ, 747, 61
Yee, H. K. C. 1980, ApJ, 241, 894
York, D. G., et al. 2000, AJ, 120, 1579