1,471 research outputs found
The VIMOS Ultra Deep Survey. Luminosity and stellar mass dependence of galaxy clustering at z~3
We present the study of the dependence of galaxy clustering on luminosity and
stellar mass in the redshift range 2z3.5 using 3236 galaxies with robust
spectroscopic redshifts from the VIMOS Ultra Deep Survey (VUDS). We measure the
two-point real-space correlation function for four volume-limited
stellar mass and four luminosity, M absolute magnitude selected,
sub-samples. We find that the scale dependent clustering amplitude
significantly increases with increasing luminosity and stellar mass indicating
a strong galaxy clustering dependence on these properties. This corresponds to
a strong relative bias between these two sub-samples of b/b=0.43.
Fitting a 5-parameter HOD model we find that the most luminous and massive
galaxies occupy the most massive dark matter haloes with
M = 10 h M. Similar to the
trends observed at lower redshift, the minimum halo mass M depends on
the luminosity and stellar mass of galaxies and grows from M
=10 hM to M=10 hM
from the faintest to the brightest among our galaxy sample, respectively. We
find the difference between these halo masses to be much more pronounced than
is observed for local galaxies of similar properties. Moreover, at z~3, we
observe that the masses at which a halo hosts, on average, one satellite and
one central galaxy is M4M over all luminosity ranges,
significantly lower than observed at z~0 indicating that the halo satellite
occupation increases with redshift. The luminosity and stellar mass dependence
is also reflected in the measurements of the large scale galaxy bias, which we
model as b(L)=1.92+25.36(L/L). We conclude our study
with measurements of the stellar-to-halo mass ratio (SHMR).Comment: 20 pages, 11 figures, A&A in press, v2. revised discussion in sec.
5.5, changed Fig. 4 and Fig. 11, added reference
The cosmic growth of the active black hole population at 1<z<2 in zCOSMOS, VVDS and SDSS
We present a census of the active black hole population at 1<z<2, by
constructing the bivariate distribution function of black hole mass and
Eddington ratio, employing a maximum likelihood fitting technique. The study of
the active black hole mass function (BHMF) and the Eddington ratio distribution
function (ERDF) allows us to clearly disentangle the active galactic nuclei
(AGN) downsizing phenomenon, present in the AGN luminosity function, into its
physical processes of black hole mass downsizing and accretion rate evolution.
We are utilizing type-1 AGN samples from three optical surveys (VVDS, zCOSMOS
and SDSS), that cover a wide range of 3 dex in luminosity over our redshift
interval of interest. We investigate the cosmic evolution of the AGN population
as a function of AGN luminosity, black hole mass and accretion rate. Compared
to z = 0, we find a distinct change in the shape of the BHMF and the ERDF,
consistent with downsizing in black hole mass. The active fraction or duty
cycle of type-1 AGN at z~1.5 is almost flat as a function of black hole mass,
while it shows a strong decrease with increasing mass at z=0. We are witnessing
a phase of intense black hole growth, which is largely driven by the onset of
AGN activity in massive black holes towards z=2. We finally compare our results
to numerical simulations and semi-empirical models and while we find reasonable
agreement over certain parameter ranges, we highlight the need to refine these
models in order to match our observations.Comment: 31 pages, 28 figures, accepted for publication in MNRA
Hubble Space Telescope Imaging in the Chandra Deep Field South: III. Quantitative Morphology of the 1Ms Chandra Counterparts and Comparison with the Field Population
We present quantitative morphological analyses of 37 HST/WFPC2 counterparts
of X-ray sources in the 1 Ms Chandra Deep Field-South (CDFS). We investigate:
1) 1-D surface brightness profiles via isophotal ellipse fitting; 2) 2-D, PSF-
convolved, bulge+disk+nucleus profile-fitting; 3) asymmetry and concentration
indices compared with all ~3000 sources in our three WFPC2 fields; and 4) near-
neighbor analyses comparing local environments of X-ray sources versus the
field control sample. Significant nuclear point-source optical components
appear in roughly half of the resolved HST/WFPC2 counterparts, showing a narrow
range of F_X/F_{opt,nuc} consistent with the several HST-unresolved X-ray
sources (putative type-1 AGN) in our fields. We infer roughly half of the
HST/WFPC2 counterparts host unobscured AGN, which suggests no steep decline in
the type-1/type-2 ratio out to the redshifts z~0.5-1 typical of our sources.
The concentration indices of the CDFS counterparts are clearly larger on
average than those of the field distribution, at 5-sigma, suggesting that the
strong correlation between central black hole mass and host galaxy properties
(including concentration index) observed in nearby galaxies is already evident
by z~0.5-1. By contrast, the asymmetry index distribution of the 21 resolved
CDFS sources at I<23 is indistinguishable from the I<23 field. Moreover, the
frequency of I<23 near neighbors around the CDFS counterparts is not
significantly different from the field sample. These results, combined with
previous similar findings for local samples, suggest that recent merger/
interaction history is not a good indicator of AGN activity over a substantial
range of look-back time.Comment: 30 pages, incl. 8 figures; accepted for publication in the
Astrophysical Journa
HST Imaging in the Chandra Deep Field South: II. WFPC2 Observations of an X-Ray Flux-Limited Sample from the 1 Msec Chandra Catalog
We present HST/WFPC2 observations of a well-defined sample of 40 X-ray
sources with X-ray fluxes above the detection threshold of the full 1 Msec
Chandra Deep Field South (CDFS). The sensitivity and spatial resolution of our
HST observations are sufficient to detect the optical counterparts of 37 of the
X-ray sources, yielding information on their morphologies and environments. In
this paper we extend the results obtained in our previous study on the 300 ks
CDFS X-ray data (Schreier et al. 2001, Paper I). Specifically, we show that the
optical counterparts to the X-ray sources are divided into two distinct
populations: 1) an optically faint group with relatively blue colors, similar
to the faint blue field galaxy population, and 2) an optically brighter group,
including resolved galaxies with average colors significantly redder than the
corresponding bright field galaxy population. The brighter objects comprise a
wide range of types, including early and late type galaxies, starbursts, and
AGN. By contrast, we show that the faint blue X-ray population are most
consistent with being predominantly Type 2 AGN of low to moderate luminosity,
located at higher redshifts (z ~ 1 - 2). This conclusion is supported by
luminosity function models of the various classes of objects. Hence, the
combination of deep X-ray data with the high spatial resolution of HST are for
the first time allowing us to probe the faint end of the AGN luminosity
function at cosmologically interesting redshifts.Comment: AASTEX-Latex, 25 pages, 4 postscript figures, 9 jpg figures. Accepted
by the Astrophysical Journal. Full-size postscript images and figures,
included in the preprint, are available from:
http://www.stsci.edu/~koekemoe/papers/cdfs-hst
Recovering the properties of high redshift galaxies with different JWST broad-band filters
Imaging with the James Webb Space Telescope (JWST) will allow for observing
the bulk of distant galaxies at the epoch of reionisation. The recovery of
their properties, such as age, color excess E(B-V), specific star formation
rate (sSFR) and stellar mass, will mostly rely on spectral energy distribution
fitting, based on the data provided by JWST's two imager cameras, namely the
Near Infrared Camera (NIRCam) and the Mid Infrared Imager (MIRI). In this work
we analyze the effect of choosing different combinations of NIRCam and MIRI
broad-band filters, from 0.6 {\mu}m to 7.7 {\mu}m, on the recovery of these
galaxy properties. We performed our tests on a sample of 1542 simulated
galaxies, with known input properties, at z=7-10. We found that, with only 8
NIRCam broad-bands, we can recover the galaxy age within 0.1 Gyr and the color
excess within 0.06 mag for 70% of the galaxies. Besides, the stellar masses and
sSFR are recovered within 0.2 and 0.3 dex, respectively, at z=7-9. Instead, at
z=10, no NIRCam band traces purely the {\lambda}> 4000 {\AA} regime and the
percentage of outliers in stellar mass (sSFR) increases by > 20% (> 90%), in
comparison to z=9. The MIRI F560W and F770W bands are crucial to improve the
stellar mass and the sSFR estimation at z=10. When nebular emission lines are
present, deriving correct galaxy properties is challenging, at any redshift and
with any band combination. In particular, the stellar mass is systematically
overestimated in up to 0.3 dex on average with NIRCam data alone and including
MIRI observations improves only marginally the estimation.Comment: 21 pages, 11 figures, 4 tables. Accepted for publication at the ApJ
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