321 research outputs found
Maximising the power of deep extragalactic imaging surveys with the James Webb Space Telescope
We present a new analysis of the potential power of deep, near-infrared,
imaging surveys with the James Webb Space Telescope (JWST) to improve our
knowledge of galaxy evolution. In this work we properly simulate what can be
achieved with realistic survey strategies, and utilise rigorous signal:noise
calculations to calculate the resulting posterior constraints on the physical
properties of galaxies. We explore a broad range of assumed input galaxy types
(>20,000 models, including extremely dusty objects) across a wide redshift
range (out to z~12), while at the same time considering a realistic mix of
galaxy properties based on our current knowledge of the evolving population (as
quantified through the Empirical Galaxy Generator: EGG). While our main focus
is on imaging surveys with NIRCam, spanning lambda(obs) = 0.6-5.0 microns, an
important goal of this work is to quantify the impact/added-value of: i)
parallel imaging observations with MIRI at longer wavelengths, and ii) deeper
supporting optical/UV imaging with HST (potentially prior to JWST launch) in
maximising the power and robustness of a major extragalactic NIRCam survey. We
show that MIRI parallel 7.7-micron imaging is of most value for better
constraining the redshifts and stellar masses of the dustiest (A_V > 3)
galaxies, while deep B-band imaging (reaching~28.5 AB mag) with ACS on HST is
vital for determining the redshifts of the large numbers of faint/low-mass, z <
5 galaxies that will be detected in a deep JWST NIRCam survey.Comment: 19 Pages, 11 Figures, Submitted to MNRA
The abundance of z≳10 galaxy candidates in the HUDF using deep JWST NIRCam medium-band imaging
The evolution of the galaxy stellar mass function over the last twelve billion years from a combination of ground-based and HST surveys
We present a new determination of the galaxy stellar mass function (GSMF)
over the redshift interval , derived from a combination
of ground-based and Hubble Space Telescope (HST) imaging surveys. Based on a
near-IR selected galaxy sample selected over a raw survey area of 3 deg
and spanning dex in stellar mass, we fit the GSMF with both single and
double Schechter functions, carefully accounting for Eddington bias to derive
both observed and intrinsic parameter values. We find that a double Schechter
function is a better fit to the GSMF at all redshifts, although the single and
double Schechter function fits are statistically indistinguishable by .
We find no evidence for significant evolution in , with the
intrinsic value consistent with over the full redshift range. Overall, our
determination of the GSMF is in good agreement with recent simulation results,
although differences persist at the highest stellar masses. Splitting our
sample according to location on the UVJ plane, we find that the star-forming
GSMF can be adequately described by a single Schechter function over the full
redshift range, and has not evolved significantly since . In
contrast, both the normalization and functional form of the passive GSMF
evolves dramatically with redshift, switching from a single to a double
Schechter function at . As a result, we find that while passive
galaxies dominate the integrated stellar-mass density at , they
only contribute per cent by . Finally, we provide a
simple parameterization that provides an accurate estimate of the GSMF, both
observed and intrinsic, at any redshift within the range .Comment: 24 pages, 16 figures, accepted for publication in MNRA
The VANDELS survey: Dust attenuation in star-forming galaxies at
We present the results of a new study of dust attenuation at redshifts based on a sample of star-forming galaxies from the VANDELS
spectroscopic survey. Motivated by results from the First Billion Years (FiBY)
simulation project, we argue that the intrinsic spectral energy distributions
(SEDs) of star-forming galaxies at these redshifts have a self-similar shape
across the mass range log probed by
our sample. Using FiBY data, we construct a set of intrinsic SED templates
which incorporate both detailed star formation and chemical abundance
histories, and a variety of stellar population synthesis (SPS) model
assumptions. With this set of intrinsic SEDs, we present a novel approach for
directly recovering the shape and normalization of the dust attenuation curve.
We find, across all of the intrinsic templates considered, that the average
attenuation curve for star-forming galaxies at is similar in shape
to the commonly-adopted Calzetti starburst law, with an average
total-to-selective attenuation ratio of . We show that the
optical attenuation () versus stellar mass () relation
predicted using our method is consistent with recent ALMA observations of
galaxies at in the \emph{Hubble} \emph{Ultra} \emph{Deep} \emph{Field}
(HUDF), as well as empirical relations predicted by a
Calzetti-like law. Our results, combined with other literature data, suggest
that the relation does not evolve over the redshift range
, at least for galaxies with log.
Finally, we present tentative evidence which suggests that the attenuation
curve may become steeper at log.Comment: 16 pages, 12 figures, accepted for publication in MNRA
The VANDELS survey: Dust attenuation in star-forming galaxies at
We present the results of a new study of dust attenuation at redshifts based on a sample of star-forming galaxies from the VANDELS
spectroscopic survey. Motivated by results from the First Billion Years (FiBY)
simulation project, we argue that the intrinsic spectral energy distributions
(SEDs) of star-forming galaxies at these redshifts have a self-similar shape
across the mass range log probed by
our sample. Using FiBY data, we construct a set of intrinsic SED templates
which incorporate both detailed star formation and chemical abundance
histories, and a variety of stellar population synthesis (SPS) model
assumptions. With this set of intrinsic SEDs, we present a novel approach for
directly recovering the shape and normalization of the dust attenuation curve.
We find, across all of the intrinsic templates considered, that the average
attenuation curve for star-forming galaxies at is similar in shape
to the commonly-adopted Calzetti starburst law, with an average
total-to-selective attenuation ratio of . We show that the
optical attenuation () versus stellar mass () relation
predicted using our method is consistent with recent ALMA observations of
galaxies at in the \emph{Hubble} \emph{Ultra} \emph{Deep} \emph{Field}
(HUDF), as well as empirical relations predicted by a
Calzetti-like law. Our results, combined with other literature data, suggest
that the relation does not evolve over the redshift range
, at least for galaxies with log.
Finally, we present tentative evidence which suggests that the attenuation
curve may become steeper at log.Comment: 16 pages, 12 figures, accepted for publication in MNRA
Search of sub-parsec massive binary black holes through line diagnosis II
Massive black hole binaries at sub-parsec separations may display in their
spectra anomalously small flux ratios between the MgII and CIV broad emission
lines, i.e. F_MgII/F_CIV <~ 0.1, due to the erosion of the broad line region
around the active, secondary black hole, by the tidal field of the primary. In
Paper I by Montuori et al. (2011), we focussed on broad lines emitted by gas
bound to the lighter accreting member of a binary when the binary is at the
center of a hollow density region (the gap) inside a circum-binary disc. The
main aim of this new study is at exploring the potential contribution to the
broad line emission by the circum-binary disc and by gaseous streams flowing
toward the black hole through the gap. We carry out a post-process analysis of
data extracted from a SPH simulation of a circum-binary disc around a black
hole binary. Our main result is that the MgII to CIV flux ratio can be reduced
to ~ 0.1 within an interval of sub-pc binary separations of the order of a ~
(0.01-0.2)(f_Edd/0.1)^(1/2) pc corresponding to orbital periods of ~ (20-200)
(f_Edd/0.1)^(3/4) years for a secondary BH mass in the range M_2 ~ 10^7-10^9
M_sun and a binary mass ratio of 0.3. At even closer separations this ratio
returns to increase to values that are indistinguishable from the case of a
single AGN (typically F_MgII/F_CIV ~ 0.3-0.4) because of the contribution to
the MgII line from gas in the circum-binary disc.Comment: 7 pages, 3 figure, accepted for publication in MNRA
T-PHOT: A new code for PSF-matched, prior-based, multiwavelength extragalactic deconfusion photometry
We present T-PHOT, a publicly available software aimed at extracting accurate
photometry from low-resolution images of deep extragalactic fields, where the
blending of sources can be a serious problem for the accurate and unbiased
measurement of fluxes and colours. T-PHOT has been developed within the
ASTRODEEP project and it can be considered as the next generation to TFIT,
providing significant improvements above it and other similar codes. T-PHOT
gathers data from a high-resolution image of a region of the sky, and uses it
to obtain priors for the photometric analysis of a lower resolution image of
the same field. It can handle different types of datasets as input priors: i) a
list of objects that will be used to obtain cutouts from the real
high-resolution image; ii) a set of analytical models; iii) a list of
unresolved, point-like sources, useful e.g. for far-infrared wavelength
domains. We show that T-PHOT yields accurate estimations of fluxes within the
intrinsic uncertainties of the method, when systematic errors are taken into
account (which can be done thanks to a flagging code given in the output).
T-PHOT is many times faster than similar codes like TFIT and CONVPHOT (up to
hundreds, depending on the problem and the method adopted), whilst at the same
time being more robust and more versatile. This makes it an optimal choice for
the analysis of large datasets. In addition we show how the use of different
settings and methods significantly enhances the performance. Given its
versatility and robustness, T-PHOT can be considered the preferred choice for
combined photometric analysis of current and forthcoming extragalactic optical
to far-infrared imaging surveys. [abridged]Comment: 23 pages, 20 figures, 2 table
The HELLAS2XMM survey. X. The bolometric output of luminous obscured quasars: The Spitzer perspective
Aims: We aim at estimating the spectral energy distributions (SEDs) and the
physical parameters related to the black holes harbored in eight high
X-ray-to-optical (F_X/F_R>10) obscured quasars at z>0.9 selected in the 2--10
keV band from the HELLAS2XMM survey.
Methods: We use IRAC and MIPS 24 micron observations, along with optical and
Ks-band photometry, to obtain the SEDs of the sources. The observed SEDs are
modeled using a combination of an elliptical template and torus emission (using
the phenomenological templates of Silva et al. 2004) for six sources associated
with passive galaxies; for two point-like sources, the empirical SEDs of red
quasars are adopted. The bolometric luminosities and the M_BH-L_K relation are
used to provide an estimate of the masses and Eddington ratios of the black
holes residing in these AGN.
Results: All of our sources are detected in the IRAC and MIPS (at 24 micron)
bands. The SED modeling described above is in good agreement with the observed
near- and mid-infrared data. The derived bolometric luminosities are in the
range ~10^45-10^47 erg s^-1, and the median 2--10 keV bolometric correction is
~25, consistent with the widely adopted value derived by Elvis et al. (1994).
For the objects with elliptical-like profiles in the K_s band, we derive high
stellar masses (0.8-6.2)X10^11 Mo, black hole masses in the range
(0.2-2.5)X10^9 Mo, and Eddington ratios L/L_Edd<0.1, suggesting a low-accretion
phase.Comment: 12 pages, 6 figures, A&A accepted. Typo corrected in the titl
The connection between stellar mass, age and quenching timescale in massive quiescent galaxies at
We present a spectro-photometric study of a mass-complete sample of quiescent
galaxies at with
drawn from the
VANDELS survey, exploring the relationship between stellar mass, age and
star-formation history. Within our sample of 114 galaxies, we derive a
stellar-mass vs stellar-age relation with a slope of Gyr
per decade in stellar mass. When combined with recent literature results, we
find evidence that the slope of this relation remains consistent over the
redshift interval . The galaxies within the VANDELS quiescent display a
wide range of star-formation histories, with a mean star-formation timescale of
Gyr and a mean quenching timescale of Gyr. We also
find a large scatter in the quenching timescales of the VANDELS quiescent
galaxies, in agreement with previous evidence that galaxies at cease
star formation via multiple mechanisms. We then focus on the oldest galaxies in
our sample, finding that the number density of galaxies that quenched before with stellar masses is . Although
uncertain, this estimate is in good agreement with the latest observational
results at , tentatively suggesting that neither rejuvenation nor merger
events are playing a major role in the evolution of the oldest massive
quiescent galaxies within the redshift interval .Comment: Accepted for publication in MNRAS, 11 pages, 6 figure
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