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.
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.
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.
The habitability of Proxima Centauri b - I. Irradiation, rotation and volatil...Sérgio Sacani
Proxima b is a planet with a minimum mass of 1.3 M⊕ orbiting within the habitable zone (HZ) of Proxima Centauri, a very low-mass,
active star and the Sun’s closest neighbor. Here we investigate a number of factors related to the potential habitability of Proxima b
and its ability to maintain liquid water on its surface. We set the stage by estimating the current high-energy irradiance of the planet
and show that the planet currently receives 30 times more EUV radiation than Earth and 250 times more X-rays. We compute the time
evolution of the star’s spectrum, which is essential for modeling the flux received over Proxima b’s lifetime. We also show that Proxima
b’s obliquity is likely null and its spin is either synchronous or in a 3:2 spin-orbit resonance, depending on the planet’s eccentricity and
level of triaxiality. Next we consider the evolution of Proxima b’s water inventory. We use our spectral energy distribution to compute
the hydrogen loss from the planet with an improved energy-limited escape formalism. Despite the high level of stellar activity we find
that Proxima b is likely to have lost less than an Earth ocean’s worth of hydrogen (EOH) before it reached the HZ 100–200 Myr after
its formation. The largest uncertainty in our work is the initial water budget, which is not constrained by planet formation models. We
conclude that Proxima b is a viable candidate habitable planet.
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.
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.
Radial velocity monitoring has found the signature of a Msin i = 1:3 M planet located within the Habitable Zone of Proxima
Centauri, the Sun’s closest neighbor (Anglada-Escudé et al. 2016). Despite a hotter past and an active host star the planet Proxima b
could have retained enough volatiles to sustain surface habitability (Ribas et al. 2016). Here we use a 3D Global Climate Model (GCM)
to simulate Proxima b’s atmosphere and water cycle for its two likely rotation modes (the 1:1 and 3:2 spin-orbit resonances) while
varying the unconstrained surface water inventory and atmospheric greenhouse eect (represented here with a CO2-N2 atmosphere.)
We find that a broad range of atmospheric compositions can allow surface liquid water. On a tidally-locked planet with a surface water
inventory larger than 0.6 Earth ocean, liquid water is always present (assuming 1 bar of N2), at least in the substellar region. Liquid
water covers the whole planet for CO2 partial pressures & 1 bar. For smaller water inventories, water can be trapped on the night side,
forming either glaciers or lakes, depending on the amount of greenhouse gases. With a non-synchronous rotation, a minimum CO2
pressure of 10 mbar (assuming 1 bar of N2) is required to avoid falling into a completely frozen snowball state if water is abundant.
If the planet is dryer, 0.5 bar of CO2 would suce to prevent the trapping of any arbitrary small water inventory into polar ice
caps. More generally, any low-obliquity planet within the classical habitable zone of its star should be in one of the climate regimes
discussed here.
We use our GCM to produce reflection/emission spectra and phase curves for the dierent rotations and surface volatile inventories.
We find that atmospheric characterization will be possible by direct imaging with forthcoming large telescopes thanks to an angular
separation of 7=D at 1 m (with the E-ELT) and a contrast of 10 7. The magnitude of the planet will allow for high-resolution
spectroscopy and the search for molecular signatures, including H2O, O2, and CO2.
The observation of thermal phase curves, although challenging, can be attempted with JWST, thanks to a contrast of 210 5 at 10 m.
Proxima b will also be an exceptional target for future IR interferometers. Within a decade it will be possible to image Proxima b and
possibly determine whether this exoplanet’s surface is habitable.
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.
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.
The habitability of Proxima Centauri b - I. Irradiation, rotation and volatil...Sérgio Sacani
Proxima b is a planet with a minimum mass of 1.3 M⊕ orbiting within the habitable zone (HZ) of Proxima Centauri, a very low-mass,
active star and the Sun’s closest neighbor. Here we investigate a number of factors related to the potential habitability of Proxima b
and its ability to maintain liquid water on its surface. We set the stage by estimating the current high-energy irradiance of the planet
and show that the planet currently receives 30 times more EUV radiation than Earth and 250 times more X-rays. We compute the time
evolution of the star’s spectrum, which is essential for modeling the flux received over Proxima b’s lifetime. We also show that Proxima
b’s obliquity is likely null and its spin is either synchronous or in a 3:2 spin-orbit resonance, depending on the planet’s eccentricity and
level of triaxiality. Next we consider the evolution of Proxima b’s water inventory. We use our spectral energy distribution to compute
the hydrogen loss from the planet with an improved energy-limited escape formalism. Despite the high level of stellar activity we find
that Proxima b is likely to have lost less than an Earth ocean’s worth of hydrogen (EOH) before it reached the HZ 100–200 Myr after
its formation. The largest uncertainty in our work is the initial water budget, which is not constrained by planet formation models. We
conclude that Proxima b is a viable candidate habitable planet.
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.
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.
Radial velocity monitoring has found the signature of a Msin i = 1:3 M planet located within the Habitable Zone of Proxima
Centauri, the Sun’s closest neighbor (Anglada-Escudé et al. 2016). Despite a hotter past and an active host star the planet Proxima b
could have retained enough volatiles to sustain surface habitability (Ribas et al. 2016). Here we use a 3D Global Climate Model (GCM)
to simulate Proxima b’s atmosphere and water cycle for its two likely rotation modes (the 1:1 and 3:2 spin-orbit resonances) while
varying the unconstrained surface water inventory and atmospheric greenhouse eect (represented here with a CO2-N2 atmosphere.)
We find that a broad range of atmospheric compositions can allow surface liquid water. On a tidally-locked planet with a surface water
inventory larger than 0.6 Earth ocean, liquid water is always present (assuming 1 bar of N2), at least in the substellar region. Liquid
water covers the whole planet for CO2 partial pressures & 1 bar. For smaller water inventories, water can be trapped on the night side,
forming either glaciers or lakes, depending on the amount of greenhouse gases. With a non-synchronous rotation, a minimum CO2
pressure of 10 mbar (assuming 1 bar of N2) is required to avoid falling into a completely frozen snowball state if water is abundant.
If the planet is dryer, 0.5 bar of CO2 would suce to prevent the trapping of any arbitrary small water inventory into polar ice
caps. More generally, any low-obliquity planet within the classical habitable zone of its star should be in one of the climate regimes
discussed here.
We use our GCM to produce reflection/emission spectra and phase curves for the dierent rotations and surface volatile inventories.
We find that atmospheric characterization will be possible by direct imaging with forthcoming large telescopes thanks to an angular
separation of 7=D at 1 m (with the E-ELT) and a contrast of 10 7. The magnitude of the planet will allow for high-resolution
spectroscopy and the search for molecular signatures, including H2O, O2, and CO2.
The observation of thermal phase curves, although challenging, can be attempted with JWST, thanks to a contrast of 210 5 at 10 m.
Proxima b will also be an exceptional target for future IR interferometers. Within a decade it will be possible to image Proxima b and
possibly determine whether this exoplanet’s surface is habitable.
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
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.
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.
T he effect_of_orbital_configuration)_on_the_possible_climates_and_habitabili...Sérgio Sacani
As lower-mass stars often host multiple rocky planets, gravitational interactions among planets can have significant
effects on climate and habitability over long timescales. Here we explore a specific case, Kepler-62f (Borucki et al.,
2013), a potentially habitable planet in a five-planet system with a K2V host star. N-body integrations reveal the
stable range of initial eccentricities for Kepler-62f is 0.00 £ e £ 0.32, absent the effect of additional, undetected
planets. We simulate the tidal evolution of Kepler-62f in this range and find that, for certain assumptions, the planet
can be locked in a synchronous rotation state. Simulations using the 3-D Laboratoire de Me´te´orologie Dynamique
(LMD) Generic global climate model (GCM) indicate that the surface habitability of this planet is sensitive to
orbital configuration.With 3 bar of CO2 in its atmosphere, we find that Kepler-62f would only be warm enough for
surface liquid water at the upper limit of this eccentricity range, providing it has a high planetary obliquity
(between 60 and 90). A climate similar to that of modern-day Earth is possible for the entire range of stable
eccentricities if atmospheric CO2 is increased to 5 bar levels. In a low-CO2 case (Earth-like levels), simulations
with version 4 of the Community Climate System Model (CCSM4) GCM and LMD Generic GCM indicate that
increases in planetary obliquity and orbital eccentricity coupled with an orbital configuration that places the
summer solstice at or near pericenter permit regions of the planet with above-freezing surface temperatures. This
may melt ice sheets formed during colder seasons. If Kepler-62f is synchronously rotating and has an ocean, CO2
levels above 3 bar would be required to distribute enough heat to the nightside of the planet to avoid atmospheric
freeze-out and permit a large enough region of open water at the planet’s substellar point to remain stable. Overall,
we find multiple plausible combinations of orbital and atmospheric properties that permit surface liquid water on
Kepler-62f. Key Words: Extrasolar planets—Habitability—Planetary environments. Astrobiology 16, xxx–xxx.
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
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,
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.
Evidence for a_distant_giant_planet_in_the_solar_systemSérgio Sacani
A descoberta de um novo planeta, atualmente não é uma manchete que chama tanto assim a atenção das pessoas. Muito disso, graças ao Telescópio Espacial Kepler, que já descobriu quase 2000 exoplanetas e todo instante uma nova descoberta é anunciada, certo? Mais ou menos, a descoberta anunciada hoje, dia 20 de Janeiro de 2016, é um pouco diferente, pois não se trata de um exoplaneta, e sim de um novo planeta no Sistema Solar, e esse é um fato que intriga os astrônomos a muitos e muitos anos.
Porém, temos que ir com calma com esses anúncios. No artigo aceito para publicação no The Astronomical Journal (artigo no final do post), os autores, Mike Brown e Konstantin Batygin, do Instituto de Tecnologia da Califórnia, apresentaram o que eles dizem ser evidências circunstâncias fortes para a existência de um grande planeta ainda não descoberto, talvez, com uma massa 10 vezes a massa da Terra, orbitando os confins do nosso Sistema Solar, muito além da órbita de Plutão. Os cientistas inferiram sua presença, por meio de anomalias encontradas nas órbitas de seis objetos do chamado Cinturão de Kuiper.
O objeto, que os pesquisadores estão chamando de Planeta Nove, não chega muito perto do Sol, no ponto mais próximo da sua órbita ele fica a 30.5 bilhões de quilômetros, ou seja, cinco vezes a distância entre o Sol e Plutão. Apesar do seu grande tamanho, ele é muito apagado, e por isso ninguém até o momento conseguiu observá-lo.
Não existe ainda uma confirmação observacional da descoberta, mas as evidências são tão fortes que fizeram com que outros especialistas como Chad Trujilo do Observatório Gemini no Havaí e David Nesvorny, do Southwest Research Institute em Boulder no Colorado, ficassem impressionados e bem convencidos de que deve mesmo haver um grande planeta nas fronteiras da nossa vizinhança cósmica.
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.
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.
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⊙.
Evidence for reflected_lightfrom_the_most_eccentric_exoplanet_knownSérgio Sacani
Planets in highly eccentric orbits form a class of objects not seen within our Solar System. The most extreme case known amongst these objects is the planet orbiting HD 20782, with an orbital period of 597 days and an eccentricity of 0.96. Here we present new data and analysis for this system as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS). We obtained CHIRON spectra to perform an independent estimation of the fundamental stellar parameters. New radial velocities from AAT and PARAS observations during periastron passage greatly improve our knowledge of the eccentric nature of the orbit. The combined analysis of our Keplerian orbital and Hipparcos astrometry show that the inclination of the planetary orbit is > 1.22◦, ruling out stellar masses for the companion. Our long-term robotic photometry show that the star is extremely stable over long timescales. Photometric monitoring of the star during predicted transit and periastron times using MOST rule out a transit of the planet and reveal evidence of phase variations during periastron. These possible photometric phase variations may be caused by reflected light from the planet’s atmosphere and the dramatic change in star–planet separation surrounding the periastron passage.
The 19 Feb. 2016 Outburst of Comet 67P/CG: An ESA Rosetta Multi-Instrument StudySérgio Sacani
On 19 Feb. 2016 nine Rosetta instruments serendipitously observed an outburst of gas and dust
from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras
and spectrometers ranging from UV over visible to microwave wavelengths, in-situ gas, dust and
plasma instruments, and one dust collector. At 9:40 a dust cloud developed at the edge of an image
in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature
of the outburst that signicantly exceeded the background. The enhancement ranged from 50% of
the neutral gas density at Rosetta to factors >100 of the brightness of the coma near the nucleus.
Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest
enhancements (factors >10). However, even the electron density at Rosetta increased by a factor 3
and consequently the spacecraft potential changed from 16V to 20V during the outburst. A
clear sequence of events was observed at the distance of Rosetta (34 km from the nucleus): within 15
minutes the Star Tracker camera detected fast particles ( 25 ms 1) while 100 m radius particles
were detected by the GIADA dust instrument 1 hour later at a speed of 6 ms 1. The slowest
were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst
originated just outside the FOV of the instruments, the source region and the magnitude of the
outburst could be determined.
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
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.
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.
T he effect_of_orbital_configuration)_on_the_possible_climates_and_habitabili...Sérgio Sacani
As lower-mass stars often host multiple rocky planets, gravitational interactions among planets can have significant
effects on climate and habitability over long timescales. Here we explore a specific case, Kepler-62f (Borucki et al.,
2013), a potentially habitable planet in a five-planet system with a K2V host star. N-body integrations reveal the
stable range of initial eccentricities for Kepler-62f is 0.00 £ e £ 0.32, absent the effect of additional, undetected
planets. We simulate the tidal evolution of Kepler-62f in this range and find that, for certain assumptions, the planet
can be locked in a synchronous rotation state. Simulations using the 3-D Laboratoire de Me´te´orologie Dynamique
(LMD) Generic global climate model (GCM) indicate that the surface habitability of this planet is sensitive to
orbital configuration.With 3 bar of CO2 in its atmosphere, we find that Kepler-62f would only be warm enough for
surface liquid water at the upper limit of this eccentricity range, providing it has a high planetary obliquity
(between 60 and 90). A climate similar to that of modern-day Earth is possible for the entire range of stable
eccentricities if atmospheric CO2 is increased to 5 bar levels. In a low-CO2 case (Earth-like levels), simulations
with version 4 of the Community Climate System Model (CCSM4) GCM and LMD Generic GCM indicate that
increases in planetary obliquity and orbital eccentricity coupled with an orbital configuration that places the
summer solstice at or near pericenter permit regions of the planet with above-freezing surface temperatures. This
may melt ice sheets formed during colder seasons. If Kepler-62f is synchronously rotating and has an ocean, CO2
levels above 3 bar would be required to distribute enough heat to the nightside of the planet to avoid atmospheric
freeze-out and permit a large enough region of open water at the planet’s substellar point to remain stable. Overall,
we find multiple plausible combinations of orbital and atmospheric properties that permit surface liquid water on
Kepler-62f. Key Words: Extrasolar planets—Habitability—Planetary environments. Astrobiology 16, xxx–xxx.
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
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,
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.
Evidence for a_distant_giant_planet_in_the_solar_systemSérgio Sacani
A descoberta de um novo planeta, atualmente não é uma manchete que chama tanto assim a atenção das pessoas. Muito disso, graças ao Telescópio Espacial Kepler, que já descobriu quase 2000 exoplanetas e todo instante uma nova descoberta é anunciada, certo? Mais ou menos, a descoberta anunciada hoje, dia 20 de Janeiro de 2016, é um pouco diferente, pois não se trata de um exoplaneta, e sim de um novo planeta no Sistema Solar, e esse é um fato que intriga os astrônomos a muitos e muitos anos.
Porém, temos que ir com calma com esses anúncios. No artigo aceito para publicação no The Astronomical Journal (artigo no final do post), os autores, Mike Brown e Konstantin Batygin, do Instituto de Tecnologia da Califórnia, apresentaram o que eles dizem ser evidências circunstâncias fortes para a existência de um grande planeta ainda não descoberto, talvez, com uma massa 10 vezes a massa da Terra, orbitando os confins do nosso Sistema Solar, muito além da órbita de Plutão. Os cientistas inferiram sua presença, por meio de anomalias encontradas nas órbitas de seis objetos do chamado Cinturão de Kuiper.
O objeto, que os pesquisadores estão chamando de Planeta Nove, não chega muito perto do Sol, no ponto mais próximo da sua órbita ele fica a 30.5 bilhões de quilômetros, ou seja, cinco vezes a distância entre o Sol e Plutão. Apesar do seu grande tamanho, ele é muito apagado, e por isso ninguém até o momento conseguiu observá-lo.
Não existe ainda uma confirmação observacional da descoberta, mas as evidências são tão fortes que fizeram com que outros especialistas como Chad Trujilo do Observatório Gemini no Havaí e David Nesvorny, do Southwest Research Institute em Boulder no Colorado, ficassem impressionados e bem convencidos de que deve mesmo haver um grande planeta nas fronteiras da nossa vizinhança cósmica.
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.
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.
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⊙.
Evidence for reflected_lightfrom_the_most_eccentric_exoplanet_knownSérgio Sacani
Planets in highly eccentric orbits form a class of objects not seen within our Solar System. The most extreme case known amongst these objects is the planet orbiting HD 20782, with an orbital period of 597 days and an eccentricity of 0.96. Here we present new data and analysis for this system as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS). We obtained CHIRON spectra to perform an independent estimation of the fundamental stellar parameters. New radial velocities from AAT and PARAS observations during periastron passage greatly improve our knowledge of the eccentric nature of the orbit. The combined analysis of our Keplerian orbital and Hipparcos astrometry show that the inclination of the planetary orbit is > 1.22◦, ruling out stellar masses for the companion. Our long-term robotic photometry show that the star is extremely stable over long timescales. Photometric monitoring of the star during predicted transit and periastron times using MOST rule out a transit of the planet and reveal evidence of phase variations during periastron. These possible photometric phase variations may be caused by reflected light from the planet’s atmosphere and the dramatic change in star–planet separation surrounding the periastron passage.
The 19 Feb. 2016 Outburst of Comet 67P/CG: An ESA Rosetta Multi-Instrument StudySérgio Sacani
On 19 Feb. 2016 nine Rosetta instruments serendipitously observed an outburst of gas and dust
from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras
and spectrometers ranging from UV over visible to microwave wavelengths, in-situ gas, dust and
plasma instruments, and one dust collector. At 9:40 a dust cloud developed at the edge of an image
in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature
of the outburst that signicantly exceeded the background. The enhancement ranged from 50% of
the neutral gas density at Rosetta to factors >100 of the brightness of the coma near the nucleus.
Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest
enhancements (factors >10). However, even the electron density at Rosetta increased by a factor 3
and consequently the spacecraft potential changed from 16V to 20V during the outburst. A
clear sequence of events was observed at the distance of Rosetta (34 km from the nucleus): within 15
minutes the Star Tracker camera detected fast particles ( 25 ms 1) while 100 m radius particles
were detected by the GIADA dust instrument 1 hour later at a speed of 6 ms 1. The slowest
were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst
originated just outside the FOV of the instruments, the source region and the magnitude of the
outburst could be determined.
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
The galaxy morphology–density relation in the EAGLE simulationSérgio Sacani
The optical morphology of galaxies is strongly related to galactic environment, with the fraction of early-type galaxies
increasing with local galaxy density. In this work, we present the first analysis of the galaxy morphology–density relation
in a cosmological hydrodynamical simulation. We use a convolutional neural network, trained on observed galaxies, to perform
visual morphological classification of galaxies with stellar masses M∗ > 1010 M in the EAGLE simulation into elliptical,
lenticular and late-type (spiral/irregular) classes. We find that EAGLE reproduces both the galaxy morphology–density and
morphology–mass relations. Using the simulations, we find three key processes that result in the observed morphology–density
relation: (i) transformation of disc-dominated galaxies from late-type (spiral) to lenticular galaxies through gas stripping in highdensity environments, (ii) formation of lenticular galaxies by merger-induced black hole feedback in low-density environments,
and (iii) an increasing fraction of high-mass galaxies, which are more often elliptical galaxies, at higher galactic densities.
The ALMA Survey of Star Formation and Evolution in Massive Protoclusters with...Sérgio Sacani
The ALMA Survey of Star Formation and Evolution in Massive Protoclusters with Blue Profiles
(ASSEMBLE) aims to investigate the process of mass assembly and its connection to high-mass star
formation theories in protoclusters in a dynamic view. We observed 11 massive (Mclump ≳ 103 M⊙),
luminous (Lbol ≳ 104 L⊙), and blue-profile (infall signature) clumps by ALMA with resolution of
∼2200–5500 au (median value of 3500 au) at 350 GHz (870 µm). 248 dense cores were identified, including 106 cores showing protostellar signatures and 142 prestellar core candidates. Compared to
early-stage infrared dark clouds (IRDCs) by ASHES, the core mass and surface density within the
ASSEMBLE clumps exhibited significant increment, suggesting concurrent core accretion during the
evolution of the clumps. The maximum mass of prestellar cores was found to be 2 times larger than
that in IRDCs, indicating that evolved protoclusters have the potential to harbor massive prestellar
cores. The mass relation between clumps and their most massive core (MMCs) is observed in ASSEMBLE but not in IRDCs, which is suggested to be regulated by multiscale mass accretion. The
mass correlation between the core clusters and their MMCs has a steeper slope compared to that
observed in stellar clusters, which can be due to fragmentation of the MMC and stellar multiplicity.
We observe a decrease in core separation and an increase in central concentration as protoclusters
evolve. We confirm primordial mass segregation in the ASSEMBLE protoclusters, possibly resulting
from gravitational concentration and/or gas accretion.
The SAMI Galaxy Sur v ey: galaxy spin is more strongly correlated with stella...Sérgio Sacani
We use the SAMI Galaxy Surv e y to examine the drivers of galaxy spin, λR e , in a multidimensional parameter space including stellar mass, stellar population age (or specific star formation rate), and various environmental metrics (local density, halo mass, satellite versus central). Using a partial correlation analysis, we consistently find that age or specific star formation rate is the primary parameter correlating with spin. Light-weighted age and specific star formation rate are more strongly correlated with spin than mass-weighted age. In fact, across our sample, once the relation between light-weighted age and spin is accounted for, there is no significant residual correlation between spin and mass, or spin and environment. This result is strongly suggestive that the present-day environment only indirectly influences spin, via the removal of gas and star formation quenching. That is, environment affects age, then age affects spin. Older galaxies then have lower spin, either due to stars being born dynamically hotter at high redshift, or due to secular heating. Our results appear to rule out environmentally dependent dynamical heating (e.g. g alaxy–g alaxy interactions) being important, at least within 1 R e where our kinematic measurements are made. The picture is more complex when we only consider high-mass galaxies ( M ∗ ≳ 10 11 M ). While the age-spin relation is still strong for these high-mass galaxies, there is a residual environmental trend with central galaxies preferentially having lower spin, compared to satellites of the same age and mass. We argue that this trend is likely due to central galaxies being a preferred location for mergers.
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.
HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxiesSérgio Sacani
Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
restframe, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong
ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
different timescales. We consider clumps located in galaxy disks, in the stripped tails and those
formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 Hα-selected
clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3750 UV-selected clumps (2026
disk clumps, 825 extraplanar clumps and 899 tail clumps). Only ∼ 15% of star-forming clumps are
spatially resolved, meaning that most are smaller than ∼ 140 pc. We study the luminosity and size
distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average
LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. Results suggest the star formation
to be turbulence driven and scale-free, as in main-sequence galaxies. All the clumps, whether they are
in the disks or in the tails, have an enhanced Hα luminosity at a given size, compared to the clumps in
main-sequence galaxies. Indeed, their Hα luminosity is closer to that of clumps in starburst galaxies,
indicating that ram pressure is able to enhance the luminosity. No striking differences are found among
disk and tail clumps, suggesting that the different environments in which they are embedded play a
minor role in influencing the star formation.
HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxiesSérgio Sacani
Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
restframe, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong
ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
different timescales. We consider clumps located in galaxy disks, in the stripped tails and those
formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 Hα-selected
clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3750 UV-selected clumps (2026
disk clumps, 825 extraplanar clumps and 899 tail clumps). Only ∼ 15% of star-forming clumps are
spatially resolved, meaning that most are smaller than ∼ 140 pc. We study the luminosity and size
distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average
LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. Results suggest the star formation
to be turbulence driven and scale-free, as in main-sequence galaxies. All the clumps, whether they are
in the disks or in the tails, have an enhanced Hα luminosity at a given size, compared to the clumps in
main-sequence galaxies. Indeed, their Hα luminosity is closer to that of clumps in starburst galaxies,
indicating that ram pressure is able to enhance the luminosity. No striking differences are found among
disk and tail clumps, suggesting that the different environments in which they are embedded play a
minor role in influencing the star formation.
HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxiesSérgio Sacani
Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
restframe, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong
ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
different timescales. We consider clumps located in galaxy disks, in the stripped tails and those
formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 Hα-selected
clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3750 UV-selected clumps (2026
disk clumps, 825 extraplanar clumps and 899 tail clumps). Only ∼ 15% of star-forming clumps are
spatially resolved, meaning that most are smaller than ∼ 140 pc. We study the luminosity and size
distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average
LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. Results suggest the star formation
to be turbulence driven and scale-free, as in main-sequence galaxies. All the clumps, whether they are
in the disks or in the tails, have an enhanced Hα luminosity at a given size, compared to the clumps in
main-sequence galaxies. Indeed, their Hα luminosity is closer to that of clumps in starburst galaxies,
indicating that ram pressure is able to enhance the luminosity. No striking differences are found among
disk and tail clumps, suggesting that the different environments in which they are embedded play a
minor role in influencing the star formation.
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.
Identification of Superclusters and Their Properties in the Sloan Digital Sky...Sérgio Sacani
Superclusters are the largest massive structures in the cosmic web, on tens to hundreds of megaparsec scales. They
are the largest assembly of galaxy clusters in the Universe. Apart from a few detailed studies of such structures,
their evolutionary mechanism is still an open question. In order to address and answer the relevant questions, a
statistically significant, large catalog of superclusters covering a wide range of redshifts and sky areas is essential.
Here, we present a large catalog of 662 superclusters identified using a modified friends-of-friends algorithm
applied on the WHL (Wen–Han–Liu) cluster catalog within a redshift range of 0.05 z 0.42. We name the most
massive supercluster at z ∼ 0.25 as the Einasto Supercluster. We find that the median mass of superclusters is
∼5.8 × 10 15 Me and the median size ∼65 Mpc. We find that the supercluster environment slightly affects the
growth of clusters. We compare the properties of the observed superclusters with the mock superclusters extracted
from the Horizon Run 4 cosmological simulation. The properties of the superclusters in the mocks and
observations are in broad agreement. We find that the density contrast of a supercluster is correlated with its
maximum extent with a power-law index, α ∼ −2. The phase-space distribution of mock superclusters shows that,
on average, ∼90% of part of a supercluster has a gravitational influence on its constituents. We also show the mock
halos’ average number density and peculiar velocity profiles in and around the superclusters.
An extreme starburst_in_the_core_of_a_rich_galaxy_cluster_at_z_1_7Sérgio Sacani
Os astrônomos descobriram um raro tipo de aglomerado de galáxias que tem seu coração repleto de novas estrelas. A descoberta inesperada, aconteceu com a ajuda dos telescópios espaciais da NASA Spitzer e Hubble, e sugere que galáxias gigantescas no núcleo desses aglomerados massivos podem crescer de maneira significante se alimentando de gás roubado de outras galáxias.
“Normalmente, as estrelas no centro dos aglomerados de galáxias, são velhas e mortas, essencialmente fósseis estelares”, disse Tracy Webb da Universidade McGill, em Montreal, no Canadá, principal autor do artigo que descreve as descobertas publicado na edição de 20 de Agosto do Teh Astrophysical Journal. “Mas nós acreditamos que a gigantesca galáxia no centro desse aglomerado está gerando novas estrelas de maneira furiosa depois de realizar uma fusão com uma galáxia menor”.
Os aglomerados de galáxias são grandes famílias de galáxias unidas e agrupadas pela gravidade. A nossa Via Láctea reside em um pequeno grupo de galáxias, chamado de Grupo Local, que por sua vez reside na periferia do gigantesco superaglomerado de galáxias Lanikea com 100000 galáxias (Lanikea signifiva “céu imensurável” em havaiano).
O aglomerado nesse novo estudo, é chamado pelos astrônomos de SpARCS1049+56, e tem no mínimo 27 galáxias, e uma massa combinada equivalente a 400 trilhões sóis. Ele está localizado a cerca de 9.8 bilhões de anos-luz na direção da constelação de Ursa Major. O objeto foi inicialmente descoberto usando o Spitzer e o Telescópio Canadá-França-Havaí, localizado no monte Mauna Kea no Havaí, e confirmado, usando o Observatório W.M. Keck, também no Mauna Kea.
The fornax deep_survey_with_vst_i_the_extended_and_diffuse_stellar_halo_of_ng...Sérgio Sacani
We have started a new deep, multi-imaging survey of the Fornax cluster, dubbed Fornax Deep
Survey (FDS), at the VLT Survey Telescope. In this paper we present the deep photometry inside
two square degrees around the bright galaxy NGC 1399 in the core of the cluster. We found that
the core of the Fornax cluster is characterised by a very extended and diffuse envelope surrounding
the luminous galaxy NGC 1399: we map the surface brightness out to 33 arcmin (∼ 192 kpc)
from the galaxy center and down to μg ∼ 31 mag arcsec−2 in the g band. The deep photometry
allows us to detect a faint stellar bridge in the intracluster region on the west side of NGC 1399
and towards NGC 1387. By analyzing the integrated colors of this feature, we argue that it
could be due to the ongoing interaction between the two galaxies, where the outer envelope of
NGC 1387 on its east side is stripped away. By fitting the light profile, we found that exists a
physical break radius in the total light distribution at R = 10 arcmin (∼ 58 kpc) that sets the
transition region between the bright central galaxy and the outer exponential halo, and that the
stellar halo contributes for 60% of the total light of the galaxy (Sec. 3.5). We discuss the main
implications of this work on the build-up of the stellar halo at the center of the Fornax cluster.
By comparing with the numerical simulations of the stellar halo formation for the most massive
BCGs (i.e. 13 < logM200/M⊙ < 14), we find that the observed stellar halo mass fraction is
consistent with a halo formed through the multiple accretion of progenitors with stellar mass in
the range 108 − 1011 M⊙. This might suggest that the halo of NGC 1399 has also gone through
a major merging event. The absence of a significant number of luminous stellar streams and
tidal tails out to 192 kpc suggests that the epoch of this strong interaction goes back to an early
formation epoch. Therefore, differently from the Virgo cluster, the extended stellar halo around
NGC 1399 is characterised by a more diffuse and well-mixed component, including the ICL.
Similar to DISCOVERY OF A GALAXY CLUSTER WITH A VIOLENTLY STARBURSTING CORE AT z = 2:506 (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.
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
Efficient spin-up of Earth System Models usingsequence accelerationSérgio Sacani
Marine and terrestrial biogeochemical models are key components of the Earth System Models (ESMs) used toproject future environmental changes. However, their slow adjustment time also hinders effective use of ESMsbecause of the enormous computational resources required to integrate them to a pre-industrial equilibrium. Here,a solution to this "spin-up" problem based on "sequence acceleration", is shown to accelerate equilibration of state-of-the-art marine biogeochemical models by over an order of magnitude. The technique can be applied in a "blackbox" fashion to existing models. Even under the challenging spin-up protocols used for Intergovernmental Panelon Climate Change (IPCC) simulations, this algorithm is 5 times faster. Preliminary results suggest that terrestrialmodels can be similarly accelerated, enabling a quantification of major parametric uncertainties in ESMs, improvedestimates of metrics such as climate sensitivity, and higher model resolution than currently feasible.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
Nutraceutical market, scope and growth: Herbal drug technologyLokesh Patil
As consumer awareness of health and wellness rises, the nutraceutical market—which includes goods like functional meals, drinks, and dietary supplements that provide health advantages beyond basic nutrition—is growing significantly. As healthcare expenses rise, the population ages, and people want natural and preventative health solutions more and more, this industry is increasing quickly. Further driving market expansion are product formulation innovations and the use of cutting-edge technology for customized nutrition. With its worldwide reach, the nutraceutical industry is expected to keep growing and provide significant chances for research and investment in a number of categories, including vitamins, minerals, probiotics, and herbal supplements.
The increased availability of biomedical data, particularly in the public domain, offers the opportunity to better understand human health and to develop effective therapeutics for a wide range of unmet medical needs. However, data scientists remain stymied by the fact that data remain hard to find and to productively reuse because data and their metadata i) are wholly inaccessible, ii) are in non-standard or incompatible representations, iii) do not conform to community standards, and iv) have unclear or highly restricted terms and conditions that preclude legitimate reuse. These limitations require a rethink on data can be made machine and AI-ready - the key motivation behind the FAIR Guiding Principles. Concurrently, while recent efforts have explored the use of deep learning to fuse disparate data into predictive models for a wide range of biomedical applications, these models often fail even when the correct answer is already known, and fail to explain individual predictions in terms that data scientists can appreciate. These limitations suggest that new methods to produce practical artificial intelligence are still needed.
In this talk, I will discuss our work in (1) building an integrative knowledge infrastructure to prepare FAIR and "AI-ready" data and services along with (2) neurosymbolic AI methods to improve the quality of predictions and to generate plausible explanations. Attention is given to standards, platforms, and methods to wrangle knowledge into simple, but effective semantic and latent representations, and to make these available into standards-compliant and discoverable interfaces that can be used in model building, validation, and explanation. Our work, and those of others in the field, creates a baseline for building trustworthy and easy to deploy AI models in biomedicine.
Bio
Dr. Michel Dumontier is the Distinguished Professor of Data Science at Maastricht University, founder and executive director of the Institute of Data Science, and co-founder of the FAIR (Findable, Accessible, Interoperable and Reusable) data principles. His research explores socio-technological approaches for responsible discovery science, which includes collaborative multi-modal knowledge graphs, privacy-preserving distributed data mining, and AI methods for drug discovery and personalized medicine. His work is supported through the Dutch National Research Agenda, the Netherlands Organisation for Scientific Research, Horizon Europe, the European Open Science Cloud, the US National Institutes of Health, and a Marie-Curie Innovative Training Network. He is the editor-in-chief for the journal Data Science and is internationally recognized for his contributions in bioinformatics, biomedical informatics, and semantic technologies including ontologies and linked data.
A brief information about the SCOP protein database used in bioinformatics.
The Structural Classification of Proteins (SCOP) database is a comprehensive and authoritative resource for the structural and evolutionary relationships of proteins. It provides a detailed and curated classification of protein structures, grouping them into families, superfamilies, and folds based on their structural and sequence similarities.
This pdf is about the Schizophrenia.
For more details visit on YouTube; @SELF-EXPLANATORY;
https://www.youtube.com/channel/UCAiarMZDNhe1A3Rnpr_WkzA/videos
Thanks...!
Lateral Ventricles.pdf very easy good diagrams comprehensive
DISCOVERY OF A GALAXY CLUSTER WITH A VIOLENTLY STARBURSTING CORE AT z = 2:506
1. Draft version August 31, 2016
Preprint typeset using LATEX style emulateapj v. 5/2/11
DISCOVERY OF A GALAXY CLUSTER WITH A VIOLENTLY STARBURSTING CORE AT z = 2.506
Tao Wang1,2
, David Elbaz1
, Emanuele Daddi1
, Alexis Finoguenov3
, Daizhong Liu4
, Corentin Schreiber5
,
Sergio Mart´ın6,7,8
, Veronica Strazzullo9
, Francesco Valentino1
, Remco van der Burg1
, Anita Zanella1
,
Laure Ciesla1
, Raphael Gobat10
, Amandine Le Brun1
, Maurilio Pannella9
, Mark Sargent11
, Xinwen Shu12
,
Qinghua Tan4
, Nico Cappelluti13
, Yanxia Li14
Draft version August 31, 2016
ABSTRACT
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∗ 1011
M ) galaxies in the central 80kpc
region (11.6σ overdensity). We have spectroscopically confirmed 17 member galaxies with 11 from CO
and the remaining ones from Hα. The X-ray luminosity, stellar mass content and velocity dispersion
all point to a collapsed, cluster-sized dark matter halo with mass M200c = 1013.9±0.2
M , 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 classified 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 field). 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.
Subject headings: galaxies: clusters — galaxies: formation — galaxies: high-redshift — cosmology
1. INTRODUCTION
Clusters of galaxies represent the densest environments
and trace the most massive dark matter (DM) halos in
the universe. Studying the formation and evolution of
galaxy clusters and their member galaxies is fundamen-
tal to our understanding of both galaxy formation and
cosmology (Kravtsov & Borgani 2012). Massive galaxy
tao.wang@cea.fr
1 Laboratoire AIM-Paris-Saclay, CEA/DSM/Irfu, CNRS, Uni-
versit´e Paris Diderot, Saclay, pt courrier 131, 91191 Gif-sur-
Yvette, France
2 Key Laboratory of Modern Astronomy and Astrophysics in
Ministry of Education, School of Astronomy and Space Sciences,
Nanjing University, Nanjing, 210093, China
3 Department of Physics, University of Helsinki, Gustaf
H¨allstr¨omin katu 2a, FI-0014 Helsinki, Finland
4 Purple Mountain Observatory, Chinese Academy of Sciences,
2 West Beijing Road, Nanjing 210008, China
5 Leiden Observatory, Leiden University, NL-2300 RA Leiden,
The Netherlands
6 European Southern Observatory, Alonso de C´ordova 3107,
Vitacura, Santiago, Chile
7 Joint ALMA Observatory, Alonso de C´ordova 3107, Vi-
tacura, Santiago, Chile
8 Institut de Radio Astronomie Millim´etrique, 300 rue de la
Piscine, Dom. Univ., F-38406, St. Martin d’H`eres, France
9 Department of Physics, Ludwig-Maximilians-Universit¨at,
Scheinerstr. 1, D-81679 M¨unchen, Germany
10 School of Physics, Korea Institute for Advanced Study, Hoe-
giro 85, Dongdaemun-gu, Seoul 130-722, Republic of Korea
11 Department of Physics and Astronomy, University of Sus-
sex, Brighton BN1 9QH, UK
12 Department of Physics, Anhui Normal University, Wuhu,
Anhui, 241000, China
13 Department of Astronomy, Yale University, New Haven, CT
06511, USA
14 Institute for Astronomy, University of Hawaii, 2680 Wood-
lawn Drive, Honolulu, HI 96822, USA
clusters in the local universe are characterized by a sig-
nificant population of massive, passive ellipticals in their
cores. Galaxy cluster archeology and numerical simula-
tions suggest that these massive clusters and their mem-
ber galaxies have experienced a rapid formation phase at
z > 2, when the bulk of the stars in central cluster galax-
ies was formed (Thomas et al. 2005; De Lucia & Blaizot
2007), and the first collapsed, cluster-sized halos (pro-
genitors of today’s most massive galaxy clusters) with
masses M200c 1014
M were assembled (Chiang et al.
2013). Observations of galaxy structures in this rapid
formation phase are critical to map the full path of galaxy
cluster formation and to answer fundamental questions
about the effect of dense environments on galaxy forma-
tion and evolution. Such structures, however, have been
so far difficult to detect due to their rareness and dis-
tance.
Extensive efforts have been made to search for high-
redshift structures during the last decade with a variety
of techniques, and a number of galaxy (proto)clusters
at z 1.5 − 2 have been discovered. A few of these
structures found up to z ∼ 2 already show evidence of
a collapsed, cluster-sized halo and exhibit a high con-
centration of quiescent galaxies in the core (with a well-
defined red sequence, Papovich et al. 2010; Gobat et al.
2011; Stanford et al. 2012; Andreon et al. 2014; Newman
et al. 2014), hence they can be classified as bona fide
mature clusters. Some of them still contain a substantial
number of star-forming galaxies (SFGs) (Brodwin et al.
2013; Gobat et al. 2013; Strazzullo et al. 2013; Clements
et al. 2014; Webb et al. 2015; Valentino et al. 2015), and a
few of them show clear evidence of a reversal of the star
arXiv:1604.07404v4[astro-ph.GA]30Aug2016
2. 2 Wang et al.
formation-density relation (Elbaz et al. 2007) with en-
hanced star formation in cluster members with respect
to field galaxies (Tran et al. 2010; Santos et al. 2015).
However, most of these clusters are already dominated
by quiescent galaxies in the core, at least at the massive
end (M∗ 1011
M ), with a significantly higher quies-
cent fraction compared to the field. Hence to probe the
main formation epoch of the most massive cluster galax-
ies, we need to explore even higher redshifts, i.e., z > 2.
Most currently known z 2 structures exhibit lower
galaxy number densities and are spread in multiple, less
massive, and not collapsed halos compared to mature
clusters (Steidel et al. 1998; Kurk et al. 2000; Venemans
et al. 2007; Chapman et al. 2009; Miley & De Breuck
2008; Daddi et al. 2009; Tanaka et al. 2011; Capak et al.
2011; Trenti et al. 2012; Hayashi et al. 2012; Spitler et al.
2012; Diener et al. 2013; Chiang et al. 2013; Koyama
et al. 2013; Lemaux et al. 2014; Yuan et al. 2014; Mei
et al. 2015; Casey et al. 2015; Kubo et al. 2016). These
structures are believed to be in various early evolutionary
stages of cluster formation, and are usually called “pro-
toclusters.” Although there is no consensus on the dis-
tinction between protoclusters and clusters, recent works
suggest that the lack of a collapsed, cluster-sized halo
(M200c 1014
M ) is a key feature to differentiate proto-
clusters from clusters (Diener et al. 2015; Muldrew et al.
2015). This distinction could be important since the
dominating environmental process that shapes galaxy
evolution depends on the mass of the host DM halo, such
as ram pressure stripping (Gunn & Gott 1972) and stran-
gulation (Larson et al. 1980). Moreover, in contrast to
mature galaxy clusters, most of the galaxies in proto-
clusters are found to be star-forming, with no clear evi-
dence of an elevated quiescent fraction compared to field
galaxies. Hence the transition between protoclusters and
mature clusters requires both the collapse of a massive,
cluster-sized halo and the formation and quenching of
a significant population of massive galaxies. Clear ev-
idence for galaxy structures in such a rapid transition
phase, however, is lacking from current observations.
From a theoretical perspective, the halo assembly his-
tory of today’s massive clusters is relatively well un-
derstood. Numerical simulations suggest that the pro-
genitor of a present day “Coma”-type galaxy cluster
(M200c > 1015
M ) exhibits overdensities of galaxies over
an extended area, 25 Mpc at z > 2, and consists of
many separated halos (Chiang et al. 2013; Muldrew et al.
2015; Contini et al. 2016). Among these halos, the most
massive one could reach a few times 1013
to 1014
M ,
and should be detected as a cluster. These results are
in good agreement with observations. However, details
on the build-up of the stellar mass content of massive
clusters and the physical mechanisms leading to the dis-
tinct galaxy population in clusters and the field are still
under active debate. Much of these debates focus on the
relative importance of different environmental effects on
massive galaxy evolution. For instance, it remains un-
clear whether the bulk population of central cluster el-
lipticals are formed after galaxies have become part of a
cluster (due to, e.g., ram pressure stripping and frequent
mergers), or whether they are already established due to
“pre-processing” in grouplike environment before their
accretion onto a cluster-sized halo (due to, e.g., stran-
gulation). A few recent theoretical studies provide some
insights into this issue, however, reaching different con-
clusions (Balogh et al. 2009; Berrier et al. 2009; McGee
et al. 2009; De Lucia et al. 2012; Granato et al. 2015;
Contini et al. 2016). The major difficulty in constraining
these theoretical models comes form the lack of compre-
hensive understanding of star formation and quenching
(quiescent fraction) in halos with different masses at high
redshifts. The fact that most galaxy clusters up to z ∼ 2
are already dominated by quiescent galaxies in the core
suggests that we need to explore structures at even higher
redshift to put observational constraints on this issue.
In this paper we report the discovery of CL
J1001+0220 (CL J1001, hereafter), a remarkable con-
centration of massive SFGs at z = 2.506 with 17 spec-
troscopic members. The detection of extended X-ray
emission and the velocity dispersion of its member galax-
ies are suggestive of a virialized, cluster-sized halo with
M200c ∼ 1013.9
M , making it the most distant X-ray-
detected galaxy cluster known to date. However, unlike
any clusters detected so far, the core of this structure
is dominated by SFGs with a star formation rate (SFR)
density of ∼ 3400M yr−1
in the central 80 kpc region,
suggesting that most of the ellipticals in this cluster will
form after galaxies accrete onto the cluster core. This
provides one of the first observational constraints on the
role of “pre-processing” in the early formation of massive
clusters.
This paper is organized as follows. We describe the
target selection and multiwavelength imaging of CL
J1001 in Section 2. Spectroscopic follow-up observa-
tions and redshift determinations are shown in Section 3.
We present the X-ray observations of the cluster from
Chandra and XMM − Newton in Section 4. In Sec-
tion 5, we discuss the global properties of the cluster.
In Section 6, we explore physical properties of its mem-
ber galaxies. We then discuss the implications of this
cluster on galaxy and cluster formation, as well as on
cosmology, in Section 7. Section 8 summarizes our main
results. Unless specified otherwise, all magnitudes are in
the AB system, and we assume cosmological parameters
of H0 = 70 km s−1
Mpc−1
, ΩM = 0.3, and ΩΛ = 0.7. A
Salpeter (1955) initial mass function (IMF) is adopted to
derive stellar masses and SFRs. When necessary, we con-
verted literature values of stellar masses and SFRs based
on the Chabrier (2003) IMF to Salpeter by multiplying
by a factor of 1.74 (0.24 dex). Throughout this paper,
we define M200c as the total halo mass contained within
R200c, the radius from the cluster center within which
the average density is 200 times the critical density at
the cluster redshift.
2. TARGET SELECTION AND MULTWAVELENGTH
IMAGING
Searching for overdensities of massive galaxies rep-
resents a relatively unbiased way of identifying galaxy
(proto)clusters at high redshifts. A number of
(proto)clusters have been identified based on overdensi-
ties of color-selected massive galaxies (Papovich et al.
2010). In particular, the distant red galaxy (DRGs,
Franx et al. (2003)) population has been shown to be
quite efficient at selecting massive galaxies (including
both quiescent and star-forming ones) at z > 2 (van
Dokkum et al. 2003). To search for galaxy clusters at
3. A galaxy cluster at z = 2.506 3
Figure 1. Left: A smoothed map of Σ10 for the whole sample of DRGs in COSMOS. The parts of the map that are affected by image
borders or bad areas are masked out. The white circle with a radius of 2 denotes the overdensity region studied in this paper, which has
the highest Σ10 value. Right: the distribution of log Σ10 values in the map and its Gaussian fit (white and orange lines, respectively). The
grayed-out part of the distribution is not considered in the fit to avoid overdensities affecting the fitting results. The white arrow shows
the peak Σ10 value of the overdensity.
z > 2, We have performed a systematic study of overden-
sities of DRGs with J − Ks > 1.3 in the COSMOS field
using a Ks-band selected catalog (Ks < 23.4, 90% com-
pleteness, McCracken et al. 2012; Muzzin et al. 2013).
Overdensities of DRGs have been shown to be good trac-
ers of potential massive structures at z > 2 (Uchimoto
et al. 2012). We constructed a galaxy surface density
map using a local galaxy density indicator, Σ10, which
is 10/(πr2
10) with r10 the distance to the 10th nearest
neighbor on a grid (Fig 1). We then fitted the distri-
bution of log(Σ10) values in the map with a gaussian
function, as shown in the right panel of Fig 1. The most
significant outlier (centered at R.A.=10:00:57.13, decl.
= +02:20:11.83) of the best-fit gaussian distribution ex-
hibits a Σ10 ∼ 11.6σ higher than the mean. We have also
tried to use different density estimators, e.g., Σ5, which is
5/(πr2
5) with r5 the distance to the 5th nearest neighbor,
yielding similar significance for this overdensity. This
overdensity includes 11 DRGs and 2 blue galaxies within
a 10” radius, or 80 kpc at z = 2.5. The photometric
redshift distribution of these 13 galaxies shows a promi-
nent peak at z ∼ 2.5 with one of them identified as a
Lyman-α emitter at z ∼ 2.5±0.1 based on intermediate-
band data (IA427 filter) in the Subaru COSMOS 20 sur-
vey (Taniguchi et al. 2015).
The same overdensity also corresponds to the bright-
est Herschel/SPIRE source (unresolved) in the region
covered by the CANDELS-Herschel survey (PI: Mark
Dickinson) in the COSMOS field (Fig. 2), with flux den-
sities of ∼ 61, 77, and 66 mJy at SPIRE 250, 350, and
500 µm, respectively. With a peak at 350 µm, the far-
infrared spectral energy distribution (SED) of this over-
density provides further evidence that most of its mem-
ber galaxies are likely at z ∼ 2.5. This overdensity was
also detected at 850 µm with SCUBA-2 (Casey et al.
2013) and 1.1mm with Aztec (Aretxaga et al. 2011) with
flux densities 14.8 and 8.9 mJy, respectively. The same
region was also observed as a candidate of lensed sources
with ALMA at band-7 (870 µm) as described in Buss-
mann et al. (2015). ALMA resolves 5 out of the 11 DRGs
in the core down to S870 µm > 1.6 mJy (Fig 3). These ob-
servations suggest that vigorous star formation is taking
place in the member galaxies of this structure. Motivated
by its high far-infrared and millimeter flux densities, we
have performed a series of follow-up observations from
near-infrared to millimeter to explore properties of this
overdensity and its member galaxies.
3. SPECTROSCOPIC OBSERVATIONS AND REDSHIFT
DETERMINATION
3.1. IRAM-NOEMA
We first conducted observations with IRAM-NOEMA
to resolve the millimeter emission and measure the red-
shift of this overdensity through the CO(5-4) line. Ob-
servations were carried out as part of a DDT program
at NOEMA between 2014 November 7th, 2014 and 2015
March 5th. Aiming at the detection of CO(5-4), we per-
formed a frequency scan between 161.1 and 171.5 GHz,
which corresponds to a redshift range of 2.36 < z < 2.58
sampled by the CO(5-4) line. We used the 3.6 GHz
instantaneous bandwidth of the WideX correlator in
three frequency setups centered at 162.9, 166.1, and
169.7 GHz. Between 1 and 1.5 hours were devoted to
each setup, reaching an rms of ∼ 13 mJy at the orig-
inal resolution, or ∼ 0.3 − 0.4 mJy over an integrated
1000 km s−1
band. Following up a preliminary detection,
we further integrated 1.8 extra hours at 164.45 GHz, and
2.4 hr at 98.68 GHz to detect the CO(3-2) transition.
Gain calibration was performed on the nearby quasars
1055+018 and 0906+015, which were also used for reg-
ular pointing and focus measurements. Calibration was
carried out with GILDAS 15
.
In total, we detected three sources in CO(5-4) down
to integrated line fluxes of ∼0.6 Jy km s−1
(5σ) in the
central 10 region, two of which were also detected in
CO(3-2). The spectroscopic redshifts of the three sources
(zspec = 2.494, 2.503, 2.513) are all consistent with being
at the same structure at z = 2.50. The CO(5-4) spectra
and intensity map are shown in Fig 4.
3.2. VLT/K-band Multi-object Spectrograph (KMOS)
15 http://www.iram.fr/IRAMFR/GILDAS
4. 4 Wang et al.
Figure 2. RGB Herschel/SPIRE composite color image of the
COSMOS field covered by the CANDELS-Herschel survey. The
R, G and B channels correspond to SPIRE 500, 350 and 250 µm,
respectively. Only sources brighter than 20 mJy at one or more
of the three SPIRE wavelengths are shown. Sources with redder
colors tend to be at higher redshifts. The large white circle with a
radius of 2 indicates the position of the galaxy overdensity, which
is the brightest SPIRE source in the whole field.
Further near-infrared spectroscopic observation with
the KMOS (Sharples et al. 2004, 2013)) on the VLT
was performed during P96 under ESO program 096.A-
0891(A) (PI: Tao Wang) in 2015 December. KMOS
is a multiplexed near-infrared integral-field spectroscopy
(IFS) system with 24 deployable integral field units over
a 7.2 diameter field. The K-band filter was used to
target the Hα emission line for candidate members at
2 < zphot < 3 in and around the overdensity. The K-
band filter covers the wavelength range 1.9 − 2.4 µm,
which corresponds to Hα at z ∼ 1.9 − 2.6. The spectral
resolution in the K-band filter is around R ∼ 4200.
The observations were prepared with the KMOS Arm
Allocator (KARMA; Wegner & Muschielok 2008) and
each pointing was observed for 450 s using a standard
object-sky-object dither pattern. The observations were
taken in good conditions with a typical seeing of 0.6-0.8 .
The total on-source exposure time for each target is ∼ 1.5
hr. Data were reduced using the ESO pipeline (version
1.3.14) in combination with custom scripts developed by
ourselves16
. We detected 11 galaxies with signal-to-noise
ratio (S/N) above 4 in Hα at z > 2 down to fHα ∼
3 × 10−17
erg s−1
cm−2
. Seven of them are at 2.494 ≤
zspec ≤ 2.512, which are consistent with being cluster
members. The spectra of these seven galaxies are shown
in Fig. 5.
3.3. VLA
Although our KMOS observation successfully detected
a number of member galaxies, none of them are located in
the core. This is likely caused by the fact that the DRGs
in the core are severely attenuated. To obtain spectro-
16 Detailed procedure and related codes are fully described here:
https://github.com/cschreib/kmos-scripts
scopic redshifts for these massive and dusty sources and
also constrain their molecular gas content, we performed
CO(1-0) Karl G. Jansky Very Large Array (JVLA) obser-
vations of the cluster core in 2015 December under VLA
program 15B-290 (PI: Tao Wang). Observations were
carried out in the D array at the Ka band. The WIDAR
correlation was configured with four spectral windows
(SPWs) of 64 channels and 2 MHz per channel resolu-
tion. The effective frequency coverage is 32.2-33.59 GHz,
corresponding to z ∼ 2.43 − 2.58 for CO(1-0).
The nearby quasar J1024-0052 was used for gain and
pointing calibration and the source 3C147 was used as
flux calibrator. The effective integration time is ∼ 10
hr. The data were reduced using the Common Astron-
omy Software Application (CASA) package (McMullin
et al. 2007), and were imaged using the CLEAN algo-
rithm in CASA with a natural weighting scheme. More
details on data reduction and molecular gas content of
individual galaxies will be presented in a future work
(T. Wang et al. 2016, in preparation). Eleven galaxies
were detected in CO(1-0) down to integrated line fluxes
0.05 Jy km s−1
, including all the 3 CO(5-4) detections
by IRAM/NOEMA and 1 Hα detection by VLT/KMOS.
Example CO(1-0) spectra of ALMA-detected galaxies in
the cluster core are shown in Fig. 6. Combining spec-
troscopic redshifts determined from IRAM-NOEMA and
VLT/KMOS, we have in total spectroscopic redshifts for
21 galaxies extending up to ∼ 1 Mpc from the over-
density. Fig 7 shows the redshift distribution of these
galaxies, which reveals a prominent spike at z ∼ 2.50.
The biweight mean of the redshifts of these 21 galaxies
yields zmean = 2.506 with 17 galaxies falling in the range
zspec = 2.506 ± 0.012. The other five galaxies deviates
from the mean by > 3σ. The redshift histogram distri-
bution around the biweight mean is well described by a
Gaussian profile. A maximum likelihood estimation of
the dispersion with the 17 galaxies yielded σz = 0.006,
and all the 17 galaxies fall in zmean ± 3 ∗ σz, hence are
classified as cluster members. Spectroscopic redshifts of
these 17 galaxies are listed in Table. 1.
4. XMM − NEWTON AND CHANDRA IMAGING
We combined the latest Chandra and XMM−Newton
surveys of the COSMOS field (Cappelluti et al. 2009;
Elvis et al. 2009; Civano et al. 2016) to search for ex-
tended emission at a 16” spatial scale with wavelet-based
detection techniques in the whole field. The depth of the
Chandra and XMM − Newton survey reaches ∼ 160
ks and ∼ 60 ks per pointing, respectively. We co-added
the XMM and Chandra background-subtracted count
images and computed the total exposure. The proce-
dure has been described in Finoguenov et al. (2009) and
shown to work even to much longer exposures such as
those of CDFS in Finoguenov et al. (2015). We used
detailed background modeling developed and verified in
previous works (Cappelluti et al. 2013; Erfanianfar et al.
2013; Finoguenov et al. 2015). A number of significant
detections (> 4σ) associated with galaxy overdensities at
high redshift were discovered (A. Finoguenov et al. 2016,
in prep). The cluster reported in this paper exhibits the
most prominent galaxy overdensity which is also in the
most advanced stage of follow-up observations.
At the position of the cluster we did not detect any
significant emission on scales smaller than 16 (Fig 8),
5. A galaxy cluster at z = 2.506 5
a b
Figure 3. RGB composite color image of the region around the cluster core. The R, G and B channel correspond to the Ks, J and
Y bands from the UltraVISTA survey, respectively. The left panel (a) corresponds to a 4 × 4 region while the right panel (b) is an
enlarged image of the central 30 × 30 region around the cluster core. Red arrows indicate distant red galaxies (DRGs) outside the core
with zphot = 2.5 ± 0.5 while white arrows indicate spectroscopically confirmed members within 3σ of the peak of the redshift distribution
(zspec = 2.506 ± 0.018), including 7 galaxies in the core (indicated in the right panel) and 10 galaxies in the outskirts. Extended X-ray
emission (0.5-2 keV) and ALMA 870 µm continuum are overlaid, respectively, with yellow and white contours in the right panel. There
are 11 DRGs (5 detected with ALMA at 870 µm) and 2 blue galaxies within the central 10 region, or 80 kpc at z = 2.5.
z=2.500
Figure 4. ALMA and IRAM-NOEMA observations of the cluster core. ALMA 870 µm continuum map of the cluster core (20 × 20 ),
overlaid with CO(5-4) emission line detections from IRAM-NOEMA. In total, five sources in the cluster are detected with ALMA, three of
which are also detected in CO(5-4) with NOEMA. The ALMA and NOEMA beams are denoted by the small and large ellipses, respectively.
The CO(5-4) line spectra for the three sources are shown in the right panel. The zero velocity of all the spectra corresponds to CO(5-4) at
z = 2.5. The area filled with colors indicate the regions where positive emission is detected.
6. 6 Wang et al.
Figure 5. Extracted and smoothed one-dimensional K-band KMOS spectra (left) and the corresponding S/N plot (right) for cluster
members. The best-fit FWHM of each Hα line is indicated in the right panels, which was used to smooth the spectra. All the listed sources
are detected with a S/N > 5 except source 130359, which is detected at 4.9σ. Though in most cases we have only detected one line, given
the range of their photometric redshifts (Table. 1) we determined their redshifts assuming the line to be Hα. The position of the Hα line
is indicated by the solid line while dotted lines show the expected position of [NII] as well as the [SII] doublet.
7. A galaxy cluster at z = 2.506 7
Figure 6. Spectra of CO(1-0) emission for the four (out of five)
ALMA detections that were detected in CO(1-0) with S/N > 5.
The blue lines show the moving average of the spectra while the
red lines show the best-fitting Gaussian profile.
which eliminates the possibility of a point-source ori-
gin of the X-ray emission. With the selected detection
threshold of 4σ, the possibility of detecting such a source
by chance in the Chandra COSMOS survey can be re-
jected at 99.5% confidence. Roughly 90% of the 4σ de-
tections are associated with a galaxy overdensity (down
to Ks < 23.4), with the one discussed in this paper being
the most extreme case. The extended X-ray emission, to-
gether with the high number of matching spectroscopic
redshifts, safeguards the detection from being a mere pro-
jection on the sky.
In order to derive the X-ray flux of the cluster, we used
two apertures of radius 20 and 32 . The 20 aperture
matches the extent of the detection while the 32 aper-
ture matches the expected size (r500c) of the emission
of the cluster, albeit with lower S/N. After a standard
background subtraction, we measured the net counts in
the soft-band image (0.5−2 keV) for the small and large
apertures, which are 57±15 and 78±23, respectively. To
determine the total flux of the cluster, we started from
the flux encompassing these two apertures and iteratively
extrapolated them to r500c. This iterative procedure is
fully described in Finoguenov et al. (2007). In each step
a correction factor is applied to the aperture flux as-
suming a β-model of the cluster brightness profile and
an initial guess of r500c, then a new r500c is estimated
and a new correction factor is applied until it converges.
The final estimate of r500c of the cluster is 24 (or ∼185
kpc at z = 2.5), and the total flux within r500c deter-
Figure 7. Redshift distributions of the galaxies in and around the
overdensity. The histogram in red shows the redshift distribution
for all DRGs within 2 from the core of the structure. DRGs with
spectroscopic redshift are indicated by the line-filled histogram.
The inner panel shows the redshift distribution of all the galaxies
in and around the overdensity (including non-DRGs) with spectro-
scopic redshift 2.45 < zspec < 2.55 from our spectroscopic surveys.
mined based on the two apertures are 5.4 ± 1.4 × 10−16
and 6.9 ± 2.0 × 10−16
erg cm−2
s−1
, respectively. The
differences in the extrapolated estimates from the two
apertures are attributed to the systematic errors and are
small compared to the expected scatter in the LX −Mhalo
relation of ∼20% in mass for our method (Allevato et al.
2012). Since the 32 aperture is larger than the final esti-
mate of r500c, no flux extrapolation is needed. We hence
take the flux measured from the 32 aperture as our total
flux estimate. This flux translates to an X-ray luminos-
ity of L0.1−2.4 keV = 8.8 ± 2.6 × 1043
erg s−1
at z = 2.5
with a K-correction from 0.5 to 2 keV to rest-frame 0.1-
2.4 keV of 2.66. This X-ray luminosity measured in r500c
is also used for calibrating the X-ray luminosity, LX, to
weak lensing mass at redshifts up to 1 (Leauthaud et al.
2010).
While the non-detection at smaller scales suggests that
the X-ray flux does not originate from a single galaxy, we
investigate the possible contribution from combined star
formation activities of the member galaxies. The aggre-
gated infrared luminosity estimated from the combined
infrared flux in the core, 1013.2
L , translates to an X-
ray luminosity L0.5−2 kev = 1.26×1043
erg s−1
assuming
the calibrated LX − SFR relation (Ranalli et al. 2003).
Therefore we estimate that at most ∼14% of the X-ray
flux originates from star formation.
We also examine the possibility that the extended X-
ray emission originated from inverse Compton (IC) scat-
tering of the cosmic microwave background (CMB) pho-
tons by relativistic electrons in the central radio source.
We argue that this is unlikely to be the case. The
few structures/galaxies with extensive IC extended X-ray
emission are mostly strong and extended radio galaxies
(usually with strong jets, Fabian et al. 2003; Overzier
et al. 2005; Johnson et al. 2007), with radio fluxes one to
two orders of magnitudes higher than the central, point-
like radio source of this structure. If we assume that the
8. 8 Wang et al.
Figure 8. X-ray detections (> 4σ at 0.5 − 2 kev) in the combined Chandra and XMM-Newton images on the 16” (left and middle) and
1-8” scales (right). The left panel shows a larger region (0.4◦ × 0.4◦) while the middle and right panels show the central 2 × 2 region
around the cluster core. In the right panel, it is clear that the cluster does not have any significant detection at smaller scales. The blue
contours indicate the extended emission of the cluster detected on the 16 scale.
Table 1
Measured physical properties of spectroscopically confirmed members
IDa RA DEC zzpec zphot J − Ks logM∗ Redshift determination Type
(J2000) (J2000) [M ]
128484 150.22348 2.30719 2.495 2.55 0.70 10.82 Hα SF
129305 150.23940 2.31750 2.512 2.65 0.71 10.19 Hα SF
129444 150.24875 2.31921 2.510 2.57 1.59 10.77 Hα SF
131661 150.23584 2.34488 2.501 2.64 1.57 11.03 Hα SF
131864 150.23454 2.34770 2.511 2.64 0.53 10.38 Hα SF
132636 150.22505 2.35620 2.510 2.55 0.49 10.68 Hα SF
130359 150.22899 2.32978 2.507 2.47 1.93 11.26 Hα, CO(1-0) SF
130842 150.23746 2.33612 2.515 3.04 1.77 11.12 CO(1-0) SF
130891 150.23987 2.33645 2.513 2.68 2.09 11.06 CO(1-0), CO(5-4) SF
130901 150.23923 2.33637 2.508 2.20 1.74 11.58 CO(1-0) SF
130933 150.23869 2.33683 2.504 2.28 2.23 11.29 CO(1-0) SF (radio AGN)
130949 150.23701 2.33571 2.503 2.49 1.66 11.57 CO(1-0), CO(3-2), CO(5-4) SF
131077 150.23735 2.33814 2.494 2.82 1.39 11.16 CO(1-0), CO(3-2), CO(5-4) SF
131079 150.23695 2.33748 2.502 2.57 1.46 11.36 CO(1-0) SF
132044 150.23650 2.34881 2.504 2.35 1.47 11.13 CO(1-0) SF
132627 150.23421 2.35659 2.506 2.36 1.34 10.90 CO(1-0) SF
–b 150.23419 2.33647 2.504 – 0.7 11.0 CO(1-0) SF
aIDs are from the Ks-selected catalog (Muzzin et al. 2013)
bThis source is clearly detected in the ultraVista images, but is close to a low-redshift galaxy hence was not included in the Ks-selected
catalog.
extended X-ray emission is fully produced through IC
emission form the central radio source (ID 130933), we
find that the resulting magnetic field is ∼0.5 µG (Har-
ris & Grindlay 1979), assuming a spectral slope of −1
for the radio emission. This magnetic field strength is
significantly lower (radio emission is too weak compared
to the X-ray emission) than the estimates for IC-origin
structures in the literature, 30∼180 µG (Overzier et al.
2005). Although there is still a possibility that the X-ray
emission is due to an IC ghost/fossil jet of the central ra-
dio source (in this case, the source of the IC scattering is
an older population of electrons, with a steeper spectral
slope, from a previous outburst of the radio source), the
non-detection of this structure at 324 MHz (3σ upper
limit ∼ 1.5 mJy, Smolˇci´c et al. 2014) suggests that the
spectral index is less steep than ∼ −2. Further deeper
follow-up at low frequencies would be required to fully
exclude this hypothesis, which is quite challenging with
current facilities.
5. CL J1001: A YOUNG GALAXY CLUSTER AT Z = 2.506
The high density of massive galaxies, extended X-ray
emission and velocity dispersion of this overdensity sug-
gest that it is embedded in a collapsed, cluster-sized halo,
and hence a bona fide galaxy cluster. At a redshift of
z ∼ 2.506, it is the most distant, spectroscopically con-
firmed galaxy cluster, which pushes the formation time of
galaxy clusters ∼0.7 Gyr back in cosmic time compared
to previously discovered clusters (Gobat et al. 2011). In
this section we further explore the structure and mass of
CL J1001, and compare these properties to simulations.
5.1. Structure and masses of CL J1001
On large scales, this dense galaxy concentration is sur-
rounded by a wider overdensity of DRGs at zphot ∼
9. A galaxy cluster at z = 2.506 9
Figure 9. Projected numbers (open circles) and mass densities
(filled circles) of DRGs extending to ∼ 2 Mpc from the overdensity.
The average number and mass densities of field DRGs, as denoted
by the gray and black horizontal lines, have been subtracted from
the data points. The best-fitting projected NFW profile, which has
a scale radius of Rs = 0+8
−0 kpc, is shown by the red line. The stellar
mass density profile of the mature X-ray cluster Cl J1449+0856 at
z = 2 (Gobat et al. 2011; Strazzullo et al. 2013) is shown as the
dashed line.
2.50 ± 0.35 extending up to ∼1 Mpc (Fig. 9). The mass
density profile of this structure, as calculated from these
DRGs, resembles that of CL J1449+0856, a mature X-
ray cluster with a total mass of M200c ∼ 6 × 1013
M
at z ∼ 2 (Strazzullo et al. 2013). The best-fitting pro-
jected NFW (Navarro et al. 1997) profile of this struc-
ture is consistent with a single logarithmic slope of −3,
suggesting that its host halo has a relatively high con-
centration, consistent with what has been observed in
z ∼ 1 clusters (van der Burg et al. 2014). This provides
further evidence of the existence of a virialized, cluster-
sized halo of this structure. The absolute normalization
of its mass density profile is most likely higher than Cl
J1449+0856, since our Ks-selected catalog is only com-
plete down to M∗ = 1011
M while the profile for Cl
J1449+0856 was derived using a galaxy catalog complete
down to 1010
M .
We estimated the total halo mass of CL J1001 with
three different methods, which are based on the X-ray
luminosity, velocity dispersion, and the stellar mass con-
tent, respectively. Using the established LX −Mhalo cor-
relation in Leauthaud et al. (2010), the total X-ray lumi-
nosity of CL J1001, L0.1−2.4keV = 8.8±2.6×1043
erg s−1
,
corresponds to a total halo mass M200c ∼ 1013.7±0.2
M ,
which is comparable to that of the mature galaxy cluster
CL J1449+0856 at z ∼ 2 (Gobat et al. 2011). While the
redshift evolution in the LX −Mhalo scaling relation used
here is based on studies of clusters at z < 1, similar stud-
ies including more distant clusters yield consistent red-
shift evolution up to z ∼ 1.5 (Reichert et al. 2011). The
same scaling relation was also shown to be valid at z ∼ 2
based on comparisons of the halo masses inferred from
clustering analysis and stacked X-ray signals (B´ethermin
et al. 2014). Moreover, most of the detected deviations
in the expected evolution in the LX − Mhalo relation is
driven by the evolution of the cool cores (Reichert et al.
2011). We assume 10% of the emission to come from the
cool core, which is typical for clusters studied in Leau-
thaud et al. (2010). Given the absence of the detection
on smaller scales, a dominant contribution of the cool
core to the total luminosity of this cluster can be ruled
out.
Galaxy cluster velocity dispersion provides another re-
liable tool for measuring cluster mass (Evrard et al. 2008;
Munari et al. 2013; Saro et al. 2013). But we also note
the large uncertainties in estimating mass for an individ-
ual cluster with velocity dispersion due to the influence
of large-scale structure in and around clusters (White
et al. 2010). The cluster redshift, z = 2.506, is deter-
mined by the biweight average of the 17 spectroscopic
members. The galaxy proper velocities vi are then de-
rived from their redshifts zi by vi = c(zi − z)/(1 + z)
(Danese et al. 1980). The line of sight velocity disper-
sion σv is the square root of the biweight sample variance
of proper velocities (Beers et al. 1990; Ruel et al. 2014),
which is estimated to be σv = 530 ± 120 km s−1
. Using
the relation between velocity dispersion and total mass
suggested in Evrard et al. (2008),
σDM(M, z) = σDM,15
h(z)M200c
1015M
α
, (1)
with σDM,15 the normalization at mass 1015
M and α
the logarithmic slope, we derived the total mass of CL
J1001 to be M200c ∼ 1013.7±0.2
M using the canonical
value of σDM,15 ∼ 1083 km s−1
and α ∼ 0.33617
. This
estimate of the total mass is in good agreement with that
derived from X-ray. We are aware that the sample used
to estimate the velocity dispersion only includes SFGs.
However, given that this cluster is dominated by SFGs
(at at least M∗ > 1011
M , where our sample is com-
plete), we do not expect that including quiescent galaxies
would change significantly the velocity dispersion estima-
tion. Nevertheless, we are planning to spectroscopically
confirm more member galaxies (including the quiescent
ones) with follow-up observations, which will further im-
prove the accuracy of the velocity dispersion estimation.
Studies of galaxy clusters at z ∼ 0 − 1.5 show that
the total stellar mass content is well correlated with the
halo mass (van der Burg et al. 2014), hence providing
another tool to infer the cluster mass. To calculate the
total stellar mass of the cluster we need to determine
which galaxies are actual cluster members. Since not all
the galaxies have spectroscopic redshifts, we have to rely
on photometric redshifts determined by Muzzin et al.
(2013). Based on the 20 galaxies with spectroscopic red-
shifts at 2 < z < 3, the normalized median absolute devi-
ation (σnmad
18
, Brammer et al. 2008) of ∆z = zphot−zspec
is σNMAD ∼ 0.033. Hence we define galaxies with red-
shifts with |z − 2.506|/ (1+2.506) < 3σnmad as candidate
members. We added stellar masses for all the DRGs
(∼ 50% have spectroscopic redshifts) with this redshift
range within R200c for a halo of M200c ∼ 1013.7
M to
determine the total stellar mass content. Field contami-
nation is further estimated and subtracted based on the
average surface number/mass density of DRGs in COS-
MOS at this redshift range.
17 We note that this relation is derived from DM-only simula-
tions, however, simulations including baryonic physics yield fully
consistent results (Munari et al. 2013).
18 σnmad = 1.48 × median
∆z−median(∆z)
1+zspec
10. 10 Wang et al.
The stellar mass of individual galaxies was derived
from SED fitting with FAST (Kriek et al. 2009). We
fit the UV to 4.5 µm photometry with the Bruzual &
Charlot (2003) stellar population synthesis models, as-
suming solar metallicity and exponentially declining star
formation histories with e-folding times τ ∼ 0.1 − 10
Gyr. We allowed the galaxies to be attenuated with
AV = 0 − 6 with the Calzetti (Calzetti et al. 2000)
attenuation law. The mass estimate is in good agree-
ment with those calculated by Muzzin et al. (2013) con-
sidering the small differences in the spectroscopic red-
shift used here and photometric redshifts used in their
work. The median stellar mass of the 11 DRGs in the
core is M∗ ∼ 1011.2
M with the two most massive
ones reaching M∗ ∼ 1011.6
M . As a reference, for
a DM halo of M200c ∼ 1013
M (with a virial radius
R200c ∼ 186 kpc) models expect only one galaxy as mas-
sive as M∗ ∼ 1011.2
M at z ∼ 2.5 (Behroozi et al. 2013),
suggesting that this overdensity resides in a very massive
halo.
We estimated the halo mass of this structure based on
the stellar mass-to-total halo mass relation calibrated for
z ∼ 1 clusters (van der Burg et al. 2014). If we add DRGs
with M∗ > 1011
M (where our sample is 90% complete),
and do not apply any correction for mass incompleteness,
we derive a combined stellar mass M∗ ∼ 2.1 × 1012
M
after correction for field contamination, which is < 10%.
If instead we correct for the incompleteness and extrap-
olate down to 109
M by assuming the same stellar mass
function as that in the field as determined from the CAN-
DELS fields (Grogin et al. 2011; Koekemoer et al. 2011;
Schreiber et al. 2015), we derived a total stellar mass
M∗ ∼ 4.3 × 1012
M , suggesting M200c ∼ 1014.6
M . The
true halo mass is most likely between the two estimates
considering that massive galaxies tend to be more abun-
dant in clusters than in the field (hence a smaller correc-
tion factor when extrapolated to lower stellar mass) as
shown at z ∼ 1 (van der Burg et al. 2013). Therefore, we
estimate that the total mass of the halo is in the range
of M200c ∼ 1013.7−14.6
M . Combined with the mass es-
timate based on X-ray and velocity dispersion, our best
estimate of the halo mass is M200c = 1013.9±0.2
M .
5.2. Comparison with simulations
We conclude that we have found a massive galaxy con-
centration embedded in a virialized, cluster-sized halo at
z = 2.506. Halos of similarly high masses at these red-
shifts are predicted to be very rare in the Λ-CDM frame-
work. The cumulative number of DM halos with z > 2.5
and M200c > 1(0.5) × 1014
M expected in the COSMOS
field is 0.01(0.3) with Planck cosmology (twice lower us-
ing WMAP 7 cosmology) (Murray et al. 2013; Planck
Collaboration et al. 2015). More accurate halo mass es-
timates and more similarly massive structures at high
redshifts are hence required to put stringent constraints
on our cosmological model.
To understand properties of this cluster in a cosmolog-
ical context, we have searched similar structures in mock
catalogs for light cones (Henriques et al. 2012, 2015)
constructed for the semi-analytic galaxy formation sim-
ulation of Guo et al. (2011), which were built on merger
trees from large DM simulations, the Millennium Simu-
lation (Springel et al. 2005) and Millennium-II (Boylan-
Figure 10. Stellar mass content versus total halo mass for massive
halos at z = 2.5±0.2 from mock catalogs. The total stellar masses
are calculated for galaxies with Ks < 23.4 mag and M∗ > 1011M
within R200c of the halo center, as defined as the most massive
galaxy in each halo. The data point for each halo is color-coded by
the number of member galaxies with M∗ > 1011M . The purple
dashed line indicates the best linear fit of the stellar mass-to-halo
mass relation based on the data points. The stellar mass estimate
for CL J1001 and its uncertainties are denoted by the red dashed
lines. The red star indicates our estimate of the halo mass and total
stellar mass (also only accounting for galaxies with M∗ > 1011M )
for CL J1001.
Kolchin et al. 2009) Simulation. These mock catalogs
include in total a ∼47 times larger area than the COS-
MOS field. We have extracted all the friends-of-friends
(FoF) halos at z = 2.5 ± 0.2 exceeding M200c = 1013
M .
We then derived the total stellar mass of galaxies with
M∗ > 1011
M in each halo, and present this total stellar
mass versus halo mass in Fig. 10. The stellar mass con-
tent of CL J1001 appears significantly higher, by a factor
of ∼ 4, than those of similarly massive halos in simula-
tions. This may indicate that the stellar mass build-up
in massive clusters at z > 2, at least for the most massive
galaxies, is more rapid than what was predicted in simu-
lations and semi-analytical models. Alternatively, it may
suggest that structures like CL J1001 are extremely rare
and are not present even in today’s largest cosmological
simulations.
Based on the evolution of the mass of the most massive
progenitor halo in simulations (Springel et al. 2005; Chi-
ang et al. 2013), a massive halo with M200c 1013.9
M
at z = 2.5 will evolve into a ∼ 2 × 1015
M halo at
z = 0, i.e., a “Coma”-type cluster (M200c > 1015
M ).
As shown in these simulations, the main progenitor (the
most massive halo) of a “Coma”-type cluster at z > 2 is
embedded in a large-scale filamentary structure spread-
ing over several tens of Mpc. Hence if CL J1001 will
evolve into a “Coma”-type cluster at z ∼ 0, then the
presence of a large-scale galaxy structure around its posi-
tion is expected. Indeed, a large-scale filamentary struc-
ture at z ∼ 2.47 whose geometric center coincides with
CL J1001 was recently spectroscopically confirmed in the
same field (Casey et al. 2015). The same region has
also been identified as a protocluster candidate at similar
redshifts based on photometric redshifts (Chiang et al.
2014). The redshift difference (2.47 versus 2.50) corre-
11. A galaxy cluster at z = 2.506 11
Figure 11. Fraction of galaxies classified as quiescent as a func-
tion of clustercentric radius. The quiescent fraction at M∗ >
1011M in this structure as well as two mature clusters at z ∼ 2
(CI J1449+0856 and JKCS 041) are shown. The quiescent fraction
is calculated for two radial bins of clustercentric radius (r < 150
kpc and 150 < r < 700 kpc), with the number of galaxies used
to calculate this fraction indicated at each data point. Error bars
are 1σ confidence level for binomial population proportions. The
shaded region indicates the quiescent fraction at the same stellar
mass at z = 2.5 ± 0.3 for field galaxies, which was derived from the
CANDELS and 3D-HST (Brammer et al. 2012) survey.
sponds to a comoving line of sight distance of ∼ 35 Mpc,
which is consistent with the extension of the progenitor
of a massive cluster at these redshifts. The presence of
this ∼30 Mpc scale overdensity surrounding CL J1001
provides further evidence that it will eventually form a
massive, “Coma”-type galaxy cluster in the present day
Universe.
6. PROPERTIES OF MEMBER GALAXIES
6.1. Star formation and Supermassive Black Hole
Accretion in the Cluster Core
While the halo mass and peak galaxy density of CL
J1001 already resemble those of low-redshift mature clus-
ters, member galaxies in the core of CL J1001 show
unusual star formation properties compared to previ-
ously discovered clusters, as indicated by the exceptional
far-infrared (FIR) and millimeter emission in the core.
Using the total infrared flux densities measured in the
core, we conducted an infrared SED fitting to derive its
infrared luminosity in order to estimate the combined
SFRs of the massive galaxies in the core. To keep the
SED fitting simple, we fit the 250 µm to 1.1mm data
points with an FIR SED consisting of a coupled single-
dust-temperature blackbody and mid-infrared power law
described in Casey (2012). We have also fitted the
SED with the Chary & Elbaz (2001) infrared SED tem-
plates. The two methods yielded similar results, LIR =
1013.2±0.1
L . This infrared luminosity translates to an
SFR of ∼ 3400M yr−1
based on the calibration in Ken-
nicutt (1998). Such high SFRs were seen in some of the
protoclusters at high redshifts (Daddi et al. 2009),how-
ever, these are quite unusual for a structure with such a
high concentration of massive galaxies, whose peak mas-
sive galaxy density is already comparable to that of ma-
ture clusters at lower redshifts.
Figure 12. Infrared SEDs for the five candidate members with
ALMA 870 µm detections. The colored solid lines show the SED
fitting results for the 5 ALMA detections while the black line shows
the SED fitting result for the combined flux densities in the core.
The 3σ upper limits for non-detections at 100 µm, 160 µm, and
1.4 GHz are shown.
We also derived the dust mass in the cluster core
from the best-fit graybody templates of the combined
SED. During the fit, the dust emissivity index is fixed
at β = 1.5 to reduce the number of free parameters.
We then converted dust masses into gas masses assum-
ing a metallicity determined from the mass-metallicity
relation at z = 2.5 (Erb et al. 2006). For the conver-
sion we assumed a metallicity corresponding to a galaxy
with M∗ ∼ 1011.2
M , the median mass of the 11 DRGs
in the core. The total dust mass is then calculated to
be Mdust = 109.3±0.1
M , translated to a molecular gas
mass of Mgas = 5 ± 1 × 1011
M . This large amount of
molecular gas and the high current SFR suggest that the
cluster core is still actively assembling its stellar mass and
will increase its mass substantially in a short timescale
despite the fact that its current stellar mass density (or
the number of massive galaxies) is already comparable
to that of mature clusters.
Only 2 out of the 11 DRGs in the 80kpc core are clas-
sified as quiescent galaxies based on the rest-frame UV J
diagram (Williams et al. 2009). Figure 11 shows the qui-
escent fraction at M∗ > 1011
M as a function of cluster-
centric radius for massive galaxies in CL J1001, as well as
for two X-ray clusters, ClJ1449+0856 and JKCS 041 at
z ∼ 2. Unlike ClJ1449+0856 and JKCS 041, which show
a quiescent fraction of 70%-100%, the quiescent fraction
in CL J1001 is significantly lower, ∼ 20%, indistinguish-
able from that in the field at the same redshifts.
The rich available data set in this structure allows us
to probe further star formation properties of individual
galaxy members. In particular, for the five ALMA de-
tections, we performed a prior-based PSF-fitting using
FASTPHOT (B´ethermin et al. 2010) at shorter wave-
lengths, i.e., 24, 100, and 160 µm to obtain the full far-
infrared SEDs. We then estimated LIR by fitting their
infrared SEDs across 24µm, 100µm, 160µm, 870 µm, and
12. 12 Wang et al.
Table 2
Infrared and radio properties of member galaxies detected with ALMA
IDa S24µm S100µm S160µm S250µm S350µm S500µm S870µm
b S1.1mm S1.8mm S1.4GHz logLIR
[mJy] [mJy] [mJy] [mJy] [mJy] [mJy] [mJy] [mJy] [mJy] [µJy] [L ]
130891 0.15±0.01 < 4.5 < 9.8 – – – 3.77±0.32 – 0.39±0.07 40±13 12.6±0.15
130901 0.04±0.01 < 4.5 < 9.8 – – – 1.66±0.21 – < 0.2 < 40 12.0±0.15
130933 0.06±0.01 < 4.5 < 9.8 – – – 2.23±0.41 – 0.24±0.07 81±15 12.2±0.15
130949 0.17±0.02 < 4.5 < 9.8 – – – 1.69±0.25 – 0.09±0.07 < 40 12.5±0.15
131077 0.28±0.02 6.3±1.7 20.1±2 – – – 5.26±0.26 – 0.63±0.07 78±13 12.8±0.10
cluster core – – – 61±6 77±6 66±6 14.8±2 8.9±2 – – 13.2±0.1
aIDs are from the Ks-selected catalog (Muzzin et al. 2013)
bflux densities for individual galaxies at 870 µm are from Bussmann et al. (2015) while the combined flux (at a slightly different wavelength,
850 µm) in the core is from Casey et al. (2013)
Figure 13. SFR-stellar mass relation for the 13 member galax-
ies in the cluster core (within 10 ). Filled circles denote galaxies
that are classified as star-forming, while open circles are galaxies
classified as quiescent based on the rest-frame U − V versus V − J
diagram. Galaxies that are detected at 870 µm with ALMA, CO(1-
0) with JVLA, and CO(5-4) with IRAM-NOEMA are respectively
denoted by red filled circles, blue open triangles, and purple open
squares. SFRs for ALMA 870 µm detected sources are derived from
their infrared luminosity while the others are from UV to NIR SED
fitting. The main sequence of field star-forming galaxies at z ∼ 2.5
and associated 0.3 dex and 0.6 dex scatter (Schreiber et al. 2015)
are shown with orange lines. The filled stars indicate the mean
value for the star-forming members in two mass bins separated at
M∗ = 1011M .
1.8 mm bandpasses using the same method as we did for
the combined SED. Fig. 12 shows the best-fit infrared
SEDs for the five galaxies detected with ALMA, as well
as the combined infrared and millimeter emission in the
cluster core. The derived LIR are listed in Table. 2. All
the five ALMA detections have LIR > 1012
L . Based
on the Kennicutt (1998) relation, the LIR of these five
galaxies adds up to an SFR ∼ 2700M yr−1
, which is
consistent with our SFR estimation using the combined
infrared SED (3400 M yr−1
) considering that some of
the star-forming members are not detected with ALMA.
For non-ALMA detected sources in the cluster core, we
estimated their SFR based on SED fitting results with
FAST.
Figure 13 presents the stellar mass-SFR relation for
galaxies in CL J1001 and their comparison with field
galaxies. The two brightest ALMA detections, or
25%(2/8)19
in terms of fraction, have SFR ∼ 4 times
higher than the main-sequence SFGs at the same mass,
indicating an elevated starburst activity in this structure
(this starburst fraction is ∼ 3 − 5% in field galaxies; El-
baz et al. 2011; Rodighiero et al. 2011; Schreiber et al.
2015). Averaging over all the star-forming members (as
shown by the filled stars in Figure 13), the mean SFR
versus stellar mass relations for these cluster SFGs fall
on the same relation within uncertainties as galaxies in
the field.
Moreover, 3 out of the 11 DRGs are detected at 1.4
GHz with F1.4GHz ∼ 70 − 80 µJy though none are de-
tected in X-rays. Two of them are classified as radio
AGNs based on their larger radio-to-IR luminosity ratio
than that for normal SFGs. This (radio) AGN fraction
(∼18%) is is much higher than that in the field ( 3.8%,
assuming that all the DRGs with 1.4 GHz detections
down to F1.4GHz 50µJy are radio AGNs), suggesting
an enhanced radio AGN activities in this dense structure.
6.2. Structural properties of member galaxies
We studied structural properties of cluster member
galaxies using HST/WFC3 J110 image (711.74 s inte-
gration time) from the HST archive (PI: M. Negrello).
Data were reduced using the IRAF MultiDrizzle pack-
age (see Negrello et al. 2014 for further details). With
the algorithm GALFIT (Peng et al. 2010) we fitted the
galaxy light distribution with a single S´ersic law (Sersic
1968). Uncertainties associated with re measurements
were derived through Monte Carlo simulations by fitting
simulated galaxies that were injected into the real image.
The J110 band corresponds to rest-frame ∼ 3300 ˚A at
z ∼ 2.5. To make a proper comparison with other stud-
ies, we corrected this size to rest-frame 5000 ˚A follow-
ing an empirically calibrated morphological k-correction
relation for quiescent and SFGs in the CANDELS
fields (van der Wel et al. 2014). Both corrections are rel-
atively small and our conclusion remains unchanged with
and without applying this morphological k-correction.
We show the mass-size relation of candidate cluster
members in Fig. 14. At M∗ > 1011
M both quiescent
and star-forming members fall on the mass-size relation
for field quiescent galaxies, which are more compact than
their local counterparts. The fact that the quiescent
members in CL J1001 are as compact as those in the
field differs from what has been found in a number of
19 If we exclude the two UV J-SFGs that fall 0.6 dex below the
star formation main sequence, the starburst fraction would be 33%.
13. A galaxy cluster at z = 2.506 13
Figure 14. Mass-size relation for quiescent and star-forming can-
didate members of the structure. Galaxies within R < 150 kpc
from the core are denoted by filled circles while those within 150
< R < 700 kpc are denoted by open circles. UV J-quiescent galax-
ies are shown in red, while UV J-star-forming galaxies are shown in
blue. The mass-size relations for quiescent and star-forming field
galaxies at z ∼ 2.5 (van der Wel et al. 2014) are shown with red
and blue lines, respectively. The 1σ scatter of the mass-size rela-
tion for field quiescent galaxies is shown with red dashed lines. The
large error bar in the bottom right indicates typical uncertainties of
mass and size measurements of our sample galaxies. The mass-size
relation for the nearby Coma cluster is indicated with the dotted
line(Andreon 1996).
mature clusters at z ∼ 1 − 2 (Papovich et al. 2012; Bas-
sett et al. 2013; Strazzullo et al. 2013; Delaye et al. 2014;
Newman et al. 2014), in which the quiescent galaxies are
less compact than their field counterparts (so-called ac-
celerated evolution of the mass-size relation in clusters).
This is consistent with the fact that CL J1001 was caught
in an earlier phase of cluster formation (right after the
collapse of the cluster-sized halo), when the cluster en-
vironment had not yet affected the structural evolution.
On the other hand, in contrast to the mass-size relation
for SFGs in the field, most of the massive star-forming
members in CL J1001 are significantly smaller and fall on
the same mass-size relation as quiescent galaxies. This
indicates that these cluster SFGs are promising progen-
itors of quiescent galaxies and may soon be quenched.
7. DISCUSSION: IMPLICATIONS OF CL J1001 ON THE
FORMATION OF MASSIVE CLUSTERS AND THEIR
MEMBER GALAXIES
With the presence of both a massive, collapsed halo
and a predominant population of massive SFGs, CL
J1001 provides a rare chance to study the rapid build-
up of a dense cluster core. The discovery of structures
in such a phase itself helps to bridge the gap between
previously discovered photoclusters and clusters at high
redshift. Its properties provide new insights into when
and how massive cluster ellipticals formed at high red-
shift.
Despite the presence of a cluster-like environment (in-
cluding both a collapsed massive halo and a high con-
centration of massive galaxies in the core), the fraction
of galaxies that are classified as quiescent in CL J1001 at
M∗ > 1011
M is estimated to be less than ∼ 20%. This
quiescent fraction is similar to that in the field and is
significantly lower than that in known z ∼ 2 mature clus-
Figure 15. HST/WFC3 J110-band stamp images of the two mas-
sive starbursts in the cluster core. The crosses mark the source
positions in the UltraVista Ks-band.
ters, suggesting that most central cluster galaxies will be
quenched only after they accrete onto the cluster. This
is different from the “pre-processing” scenario in which
galaxies are quenched in groups or large-scale filaments
prior to cluster assembly, due to, e.g., strangulation. We
speculate that this might be due to the fact that at high
redshifts, only a small fraction of cluster galaxies were ac-
creted onto the final cluster halo as a member of a group-
sized halo with M200c > 1013
M , as suggested by simula-
tions (Balogh et al. 2009; McGee et al. 2009). Moreover,
simulations suggest that cold streams can penetrate mod-
erately massive, group-sized halos with M200c ∼1013
M
at z 2 (Dekel & Birnboim 2006), which makes it dif-
ficult to fully quench protocluster galaxies even if they
were located in a group-sized halo before their accretion
onto the cluster. These arguments are also consistent
with the fact that is are no clear evidence for suppressed
star formation or an elevated quiescent fraction in proto-
cluster regions. In fact, based on current studies of z 2
protoclusters, star formation in protoclusters seems to be
elevated (Casey 2016) rather than suppressed compared
to field galaxies.
We caution that while many studies of high-redshift
protoclusters observed a high volume density of highly
SFGs or dusty galaxies (detected down to some flux level
in the far-infrared or submillimeter), it is unclear whether
this is caused by elevated SFRs in individual galaxies or
simply caused by the fact that there are more massive
galaxies in protocluster regions. A thorough examination
of the mass-star formation relation as well as the relative
fraction of quiescent and SFGs in protocluster regions,
and its comparison to field galaxies, is required to obtain
solid conclusions. This is, however, quite difficult for
protoclusters due to their extended region (several tens
of Mpc) and lower significance of galaxy overdensities,
which inhibit a census of its member galaxies (particu-
larly quiescent ones). Moreover, simulations suggest that
a significant fraction of protocluster galaxies may not end
up in clusters at z ∼ 0, especially those low-mass galax-
ies in the outskirts (Contini et al. 2016). This makes it
more complicated to compare observations of protoclus-
ters and simulations.
Although the current observed quiescent fraction in CL
J1001 is similar to that in the field, several pieces of evi-
dence suggest that this fraction will increase over a short
time scale. The total molecular gas mass for galaxies in
the core is estimated to be Mgas ∼ 5 × 1011
M (Sec-
tion 6). Considering their current SFR, this structure
will consume all the available gas within ∼ 150−200 Myr
14. 14 Wang et al.
(twice larger if using Chabrier IMF for the stellar mass
estimation). The halo mass of this structure (∼ 1014
M )
falls in the regime where the infalling gas is fully shock-
heated instead of forming cold streams (Dekel & Birn-
boim 2006). These properties suggest that the cluster
will likely form a predominant population of quiescent
galaxies in the core by z ∼ 2.2. Moreover, most of the
massive SFGs in the core already fall on the mass-size re-
lation of quiescent galaxies at the same redshift (Fig. 14),
providing further evidence that these galaxies may soon
transform into quiescent galaxies.
Compared to field galaxies, massive galaxies in the
core of CL J1001 exhibit a higher starburst fraction,
suggesting that cluster ellipticals may form their stars
through more violent starbursting events and in shorter
time scales than field galaxies. This is consistent with
galaxy cluster archeology studies (Thomas et al. 2005).
This high starburst fraction may be partly due to a
higher merger rate, as expected for this high density
region with moderate velocity dispersion. Indeed, one
of the starbursting galaxies (ID 130949) appears to be
a complex multi-component galaxy system in the high-
resolution WFC3 J110 image while the other one (ID
131077) is completely undetected due to obscuration and
also the shallow depth of J110 imaging (Fig. 15). The
high starburst fraction could be also caused by the com-
pression on the molecular gas in galaxies by the hot in-
tracluster medium (IGM), which could trigger the col-
lapse of molecular clouds and lead to efficient star for-
mation within a short timescale (Fujita & Nagashima
1999; Bekki & Couch 2003). Deeper WFC3 imaging in
the rest-frame optical and spatially resolved distribution
of both star formation and molecular gas are required to
provide further insights into these questions, which we
defer to a future work.
8. CONCLUSION
We conclude that we have found a massive galaxy over-
density at z = 2.506, which is likely to be the most dis-
tant X-ray cluster known to date. This overdensity is
embedded in a collapsed, cluster-sized halo as suggested
by its high density of massive galaxies in the core, ex-
tended X-ray emission, cluster-like mass density profile,
and velocity dispersion of member galaxies. Moreover,
this structure exhibits both a high SFR density and a
predominant population of massive SFGs in the core, in-
dicating that it is in a major formation phase for the cen-
tral massive cluster galaxies when most of them have not
been quenched. These properties differentiate this struc-
ture from other structures recently discovered at similar
redshifts and suggest that it may represent the missing
link between mature clusters and protoclusters. The fol-
lowing are our findings on its main properties and its
implications for cluster formation.
1. The structure was identified as the most signifi-
cant overdensity of DRGs in COSMOS with 11 DRGs
distributed over a 80kpc region. It is also the bright-
est Herschel/SPIRE source (unresolved) in the central
COSMOS region covered by CANDELS-Herschel survey
with flux densities 60-80 mJy in the SPIRE bands.
2. Extensive follow-up observations with IRAM-
NOEMA, VLT/KMOS, and JVLA spectroscopically con-
firmed 17 members including 7 DRGs in the core. Based
on these 17 members, the cluster redshift is determined
to be z = 2.506 with a velocity dispersion of 530 ± 120
km s−1
.
3. Combining XMM-Newton and Chandra observa-
tions of the field, the overdensity exhibits extended X-
ray emission at the 4σ confidence level with an X-ray
luminosity L0.1−2.4keV = 8.8 × 1043
erg s−1
. The X-ray
luminosity, the velocity dispersion, and the stellar mass
content of this structure all suggest a total halo mass of
M200c = 1013.9±0.2
M .
4. The structure exhibits a high star formation density
in the 80kpc core with a combined SFR ∼3400 M yr−1
and a gas depletion time of ∼200 Myr. Galaxies in the
core show both elevated starburst activities and super-
massive black hole accretion compared to field galaxies.
5. The core of this structure is dominated by SFGs
with only 2 out the 11 DRGs classified as quiescent
galaxies. At M∗ > 1011
M the quiescent fraction is
around ∼20% without significant dependence on the clus-
tercentric distance up to ∼ 700 kpc from the core. This
quiescent fraction is similar to field galaxies at the same
redshift and significantly lower than that in previously
discovered mature clusters at z ∼ 2.
6. At the massive end (M∗ > 1011
M ), both quiescent
galaxies and star-forming ones in the core of the structure
appear to be compact, which is consistent with the mass-
size relation for quiescent galaxies in the field.
One of the most prominent features of this structure is
the presence of both a collapsed, cluster-sized halo and
a high abundance of massive, highly SFGs. Its discovery
suggests that most cluster ellipticals likely formed only
after their accretion onto a cluster-sized halo, though
more similar structures are needed to confirm. Recently
a number of Planck sources with high Herschel/SPIRE
fluxes have been discovered and are likely to be z 2
(proto)cluster candidates (Planck Collaboration et al.
2015), some of which may be in massive halos similar
to this structure, although further follow-up observations
are needed for detailed comparisons. Future studies of a
large number of similar structures will definitively clarify
the formation path of massive galaxy clusters and pro-
vide critical constraints on cosmology.
We thank the anonymous referee for helpful comments
which improved the content of this paper. This study is
based on observations with the IRAM Plateau de Bure
Interferometer. IRAM is supported by INSU/CNRS
(France), MPG (Germany), and IGN (Spain). This pa-
per makes use of the data from the Karl G. Jansky
Very Large Array. The National Radio Astronomy Ob-
servatory is a facility of the National Science Founda-
tion operated under cooperative agreement by Associ-
ated Universities, Inc. This paper makes use of the fol-
lowing ALMA data: ADS/JAO.ALMA#2011.0.00539.S.
ALMA is a partnership of ESO (representing its mem-
ber states), NSF (USA), and NINS (Japan), together
with NRC (Canada), NSC, ASIAA (Taiwan), and KASI
(Republic of Korea), in cooperation with the Republic
of Chile. The Joint ALMA Observatory is operated by
ESO, AUI/NRAO, and NAOJ. This work is partly based
on observations collected at the European Organization
for Astronomical Research in the Southern Hemisphere
under ESO program 096.A-0891(A).
This research is supported by the European Commis-
15. A galaxy cluster at z = 2.506 15
sion through the FP7 SPACE project ASTRODEEP
(Ref.No: 312725). T.W. acknowledges support for this
work from the National Natural Science Foundation of
China under grant 11303014.
Facilities: HST, Herschel(PACS, SPIRE), Spitzer
(IRAC, MIPS), Chandra, XMM − Newton.
REFERENCES
Allevato, V., Finoguenov, A., Hasinger, G., et al. 2012, ApJ, 758,
47
Andreon, S. 1996, A&A, 314, 763
Andreon, S., Newman, A. B., Trinchieri, G., et al. 2014, A&A,
565, A120
Aretxaga, I., Wilson, G. W., Aguilar, E., et al. 2011, MNRAS,
415, 3831
Balogh, M. L., McGee, S. L., Wilman, D., et al. 2009, MNRAS,
398, 754
Bassett, R., Papovich, C., Lotz, J. M., et al. 2013, ApJ, 770, 58
Beers, T. C., Flynn, K., & Gebhardt, K. 1990, AJ, 100, 32
Behroozi, P. S., Wechsler, R. H., & Conroy, C. 2013, ApJ, 770, 57
Bekki, K., & Couch, W. J. 2003, ApJ, 596, L13
Berrier, J. C., Stewart, K. R., Bullock, J. S., et al. 2009, ApJ,
690, 1292
B´ethermin, M., Dole, H., Beelen, A., & Aussel, H. 2010, A&A,
512, A78
B´ethermin, M., Kilbinger, M., Daddi, E., et al. 2014, A&A, 567,
A103
Boylan-Kolchin, M., Springel, V., White, S. D. M., Jenkins, A., &
Lemson, G. 2009, MNRAS, 398, 1150
Brammer, G. B., van Dokkum, P. G., & Coppi, P. 2008, ApJ,
686, 1503
Brammer, G. B., van Dokkum, P. G., Franx, M., et al. 2012,
ApJS, 200, 13
Brodwin, M., Stanford, S. A., Gonzalez, A. H., et al. 2013, ApJ,
779, 138
Bruzual, G., & Charlot, S. 2003, MNRAS, 344, 1000
Bussmann, R. S., Riechers, D., Fialkov, A., et al. 2015, ApJ, 812,
43
Calzetti, D., Armus, L., Bohlin, R. C., et al. 2000, ApJ, 533, 682
Capak, P. L., Riechers, D., Scoville, N. Z., et al. 2011, Nature,
470, 233
Cappelluti, N., Brusa, M., Hasinger, G., et al. 2009, A&A, 497,
635
Cappelluti, N., Kashlinsky, A., Arendt, R. G., et al. 2013, ApJ,
769, 68
Casey, C. M. 2012, MNRAS, 425, 3094
—. 2016, ApJ, 824, 36
Casey, C. M., Chen, C.-C., Cowie, L. L., et al. 2013, MNRAS,
436, 1919
Casey, C. M., Cooray, A., Capak, P., et al. 2015, ApJ, 808, L33
Chabrier, G. 2003, PASP, 115, 763
Chapman, S. C., Blain, A., Ibata, R., et al. 2009, ApJ, 691, 560
Chary, R., & Elbaz, D. 2001, ApJ, 556, 562
Chiang, Y.-K., Overzier, R., & Gebhardt, K. 2013, ApJ, 779, 127
—. 2014, ApJ, 782, L3
Civano, F., Marchesi, S., Comastri, A., et al. 2016, ApJ, 819, 62
Clements, D. L., Braglia, F. G., Hyde, A. K., et al. 2014,
MNRAS, 439, 1193
Contini, E., De Lucia, G., Hatch, N., Borgani, S., & Kang, X.
2016, MNRAS, 456, 1924
Daddi, E., Dannerbauer, H., Stern, D., et al. 2009, ApJ, 694, 1517
Danese, L., de Zotti, G., & di Tullio, G. 1980, A&A, 82, 322
De Lucia, G., & Blaizot, J. 2007, MNRAS, 375, 2
De Lucia, G., Weinmann, S., Poggianti, B. M.,
Arag´on-Salamanca, A., & Zaritsky, D. 2012, MNRAS, 423,
1277
Dekel, A., & Birnboim, Y. 2006, MNRAS, 368, 2
Delaye, L., Huertas-Company, M., Mei, S., et al. 2014, MNRAS,
441, 203
Diener, C., Lilly, S. J., Knobel, C., et al. 2013, ApJ, 765, 109
Diener, C., Lilly, S. J., Ledoux, C., et al. 2015, ApJ, 802, 31
Elbaz, D., Daddi, E., Le Borgne, D., et al. 2007, A&A, 468, 33
Elbaz, D., Dickinson, M., Hwang, H. S., et al. 2011, A&A, 533,
A119
Elvis, M., Civano, F., Vignali, C., et al. 2009, ApJS, 184, 158
Erb, D. K., Shapley, A. E., Pettini, M., et al. 2006, ApJ, 644, 813
Erfanianfar, G., Finoguenov, A., Tanaka, M., et al. 2013, ApJ,
765, 117
Evrard, A. E., Bialek, J., Busha, M., et al. 2008, ApJ, 672, 122
Fabian, A. C., Sanders, J. S., Crawford, C. S., & Ettori, S. 2003,
MNRAS, 341, 729
Finoguenov, A., Guzzo, L., Hasinger, G., et al. 2007, ApJS, 172,
182
Finoguenov, A., Connelly, J. L., Parker, L. C., et al. 2009, ApJ,
704, 564
Finoguenov, A., Tanaka, M., Cooper, M., et al. 2015, A&A, 576,
A130
Franx, M., Labb´e, I., Rudnick, G., et al. 2003, ApJ, 587, L79
Fujita, Y., & Nagashima, M. 1999, ApJ, 516, 619
Gobat, R., Daddi, E., Onodera, M., et al. 2011, A&A, 526, A133
Gobat, R., Strazzullo, V., Daddi, E., et al. 2013, ApJ, 776, 9
Granato, G. L., Ragone-Figueroa, C., Dom´ınguez-Tenreiro, R.,
et al. 2015, MNRAS, 450, 1320
Grogin, N. A., Kocevski, D. D., Faber, S. M., et al. 2011, ApJS,
197, 35
Gunn, J. E., & Gott, III, J. R. 1972, ApJ, 176, 1
Guo, Q., White, S., Boylan-Kolchin, M., et al. 2011, MNRAS,
413, 101
Harris, D. E., & Grindlay, J. E. 1979, MNRAS, 188, 25
Hayashi, M., Kodama, T., Tadaki, K.-i., Koyama, Y., & Tanaka,
I. 2012, ApJ, 757, 15
Henriques, B. M. B., White, S. D. M., Lemson, G., et al. 2012,
MNRAS, 421, 2904
Henriques, B. M. B., White, S. D. M., Thomas, P. A., et al. 2015,
MNRAS, 451, 2663
Johnson, O., Almaini, O., Best, P. N., & Dunlop, J. 2007,
MNRAS, 376, 151
Kennicutt, Jr., R. C. 1998, ARA&A, 36, 189
Koekemoer, A. M., Faber, S. M., Ferguson, H. C., et al. 2011,
ApJS, 197, 36
Koyama, Y., Kodama, T., Tadaki, K.-i., et al. 2013, MNRAS,
428, 1551
Kravtsov, A. V., & Borgani, S. 2012, ARA&A, 50, 353
Kriek, M., van Dokkum, P. G., Labb´e, I., et al. 2009, ApJ, 700,
221
Kubo, M., Yamada, T., Ichikawa, T., et al. 2016, MNRAS, 455,
3333
Kurk, J. D., R¨ottgering, H. J. A., Pentericci, L., et al. 2000,
A&A, 358, L1
Larson, R. B., Tinsley, B. M., & Caldwell, C. N. 1980, ApJ, 237,
692
Leauthaud, A., Finoguenov, A., Kneib, J.-P., et al. 2010, ApJ,
709, 97
Lemaux, B. C., Cucciati, O., Tasca, L. A. M., et al. 2014, A&A,
572, A41
McCracken, H. J., Milvang-Jensen, B., Dunlop, J., et al. 2012,
A&A, 544, A156
McGee, S. L., Balogh, M. L., Bower, R. G., Font, A. S., &
McCarthy, I. G. 2009, MNRAS, 400, 937
McMullin, J. P., Waters, B., Schiebel, D., Young, W., & Golap,
K. 2007, in Astronomical Society of the Pacific Conference
Series, Vol. 376, Astronomical Data Analysis Software and
Systems XVI, ed. R. A. Shaw, F. Hill, & D. J. Bell, 127
Mei, S., Scarlata, C., Pentericci, L., et al. 2015, ApJ, 804, 117
Miley, G., & De Breuck, C. 2008, A&A Rev., 15, 67
Muldrew, S. I., Hatch, N. A., & Cooke, E. A. 2015, MNRAS, 452,
2528
Munari, E., Biviano, A., Borgani, S., Murante, G., & Fabjan, D.
2013, MNRAS, 430, 2638
Murray, S. G., Power, C., & Robotham, A. S. G. 2013,
Astronomy and Computing, 3, 23
Muzzin, A., Marchesini, D., Stefanon, M., et al. 2013, ApJS, 206,
8
Navarro, J. F., Frenk, C. S., & White, S. D. M. 1997, ApJ, 490,
493
Negrello, M., Hopwood, R., Dye, S., et al. 2014, MNRAS, 440,
1999
Newman, A. B., Ellis, R. S., Andreon, S., et al. 2014, ApJ, 788, 51
Overzier, R. A., Harris, D. E., Carilli, C. L., et al. 2005, A&A,
433, 87
16. 16 Wang et al.
Papovich, C., Momcheva, I., Willmer, C. N. A., et al. 2010, ApJ,
716, 1503
Papovich, C., Bassett, R., Lotz, J. M., et al. 2012, ApJ, 750, 93
Peng, C. Y., Ho, L. C., Impey, C. D., & Rix, H.-W. 2010, AJ,
139, 2097
Planck Collaboration, Ade, P. A. R., Aghanim, N., et al. 2015,
ArXiv e-prints, arXiv:1502.01589
Ranalli, P., Comastri, A., & Setti, G. 2003, A&A, 399, 39
Reichert, A., B¨ohringer, H., Fassbender, R., & M¨uhlegger, M.
2011, A&A, 535, A4
Rodighiero, G., Daddi, E., Baronchelli, I., et al. 2011, ApJ, 739,
L40
Ruel, J., Bazin, G., Bayliss, M., et al. 2014, ApJ, 792, 45
Salpeter, E. E. 1955, ApJ, 121, 161
Santos, J. S., Altieri, B., Valtchanov, I., et al. 2015, MNRAS, 447,
L65
Saro, A., Mohr, J. J., Bazin, G., & Dolag, K. 2013, ApJ, 772, 47
Schreiber, C., Pannella, M., Elbaz, D., et al. 2015, A&A, 575, A74
Sersic, J. L. 1968, Atlas de galaxias australes
Sharples, R., Bender, R., Agudo Berbel, A., et al. 2013, The
Messenger, 151, 21
Sharples, R. M., Bender, R., Lehnert, M. D., et al. 2004, in
Proc. SPIE, Vol. 5492, Ground-based Instrumentation for
Astronomy, ed. A. F. M. Moorwood & M. Iye, 1179–1186
Smolˇci´c, V., Ciliegi, P., Jeli´c, V., et al. 2014, MNRAS, 443, 2590
Spitler, L. R., Labb´e, I., Glazebrook, K., et al. 2012, ApJ, 748,
L21
Springel, V., Di Matteo, T., & Hernquist, L. 2005, ApJ, 620, L79
Stanford, S. A., Brodwin, M., Gonzalez, A. H., et al. 2012, ApJ,
753, 164
Steidel, C. C., Adelberger, K. L., Dickinson, M., et al. 1998, ApJ,
492, 428
Strazzullo, V., Gobat, R., Daddi, E., et al. 2013, ApJ, 772, 118
Tanaka, I., Breuck, C. D., Kurk, J. D., et al. 2011, PASJ, 63, 415
Taniguchi, Y., Kajisawa, M., Kobayashi, M. A. R., et al. 2015,
PASJ, 67, 104
Thomas, D., Maraston, C., Bender, R., & Mendes de Oliveira, C.
2005, ApJ, 621, 673
Tran, K.-V. H., Papovich, C., Saintonge, A., et al. 2010, ApJ,
719, L126
Trenti, M., Bradley, L. D., Stiavelli, M., et al. 2012, ApJ, 746, 55
Uchimoto, Y. K., Yamada, T., Kajisawa, M., et al. 2012, ApJ,
750, 116
Valentino, F., Daddi, E., Strazzullo, V., et al. 2015, ApJ, 801, 132
van der Burg, R. F. J., Muzzin, A., Hoekstra, H., et al. 2014,
A&A, 561, A79
—. 2013, A&A, 557, A15
van der Wel, A., Franx, M., van Dokkum, P. G., et al. 2014, ApJ,
788, 28
van Dokkum, P. G., F¨orster Schreiber, N. M., Franx, M., et al.
2003, ApJ, 587, L83
Venemans, B. P., R¨ottgering, H. J. A., Miley, G. K., et al. 2007,
A&A, 461, 823
Webb, T., Noble, A., DeGroot, A., et al. 2015, ApJ, 809, 173
Wegner, M., & Muschielok, B. 2008, in Proc. SPIE, Vol. 7019,
Advanced Software and Control for Astronomy II, 70190T
White, M., Cohn, J. D., & Smit, R. 2010, MNRAS, 408, 1818
Williams, R. J., Quadri, R. F., Franx, M., van Dokkum, P., &
Labb´e, I. 2009, ApJ, 691, 1879
Yuan, T., Nanayakkara, T., Kacprzak, G. G., et al. 2014, ApJ,
795, L20