60 research outputs found
The VIMOS-VLT Deep Survey. The dependence of clustering on galaxy stellar mass at z~1
Aims: We use the VVDS-Deep first-epoch data to measure the dependence of
galaxy clustering on galaxy stellar mass, at z~0.85.
Methods: We measure the projected correlation function wp(rp) for sub-samples
with 0.5<z<1.2 covering different mass ranges between 10^9 and 10^11 Msun. We
quantify in detail the observational selection biases using 40 mock catalogues
built from the Millennium run and semi-analytic models.
Results: Our simulations indicate that serious incompleteness in mass is
present only for log(M/Msun)<9.5. In the mass range log(M/Msun)=[9.0-9.5], the
photometric selection function of the VVDS misses 2/3rd of the galaxies. The
sample is virtually 100% complete above 10^10 Msun. We present the first direct
evidence for a clear dependence of clustering on the galaxy stellar mass at
z~0.85. The clustering length increases from r0 ~ 2.76 h^-1 Mpc for galaxies
with mass M>10^9 Msun to r0 ~ 4.28 h^-1 Mpc for galaxies more massive than
10^10.5 Msun. At the same time, the slope increases from ~ 1.67 to ~ 2.28.
A comparison of the observed wp(rp) to local measurements by the SDSS shows
that the evolution is faster for objects less massive than ~10^10.5 Msun. This
is interpreted as a higher dependence on redshift of the linear bias b_L for
the more massive objects. While for the most massive galaxies b_L decreases
from 1.5+/-0.2 at z~0.85 to 1.33+/-0.03 at z~0.15, the less massive population
maintains a virtually constant value b_L~1.3. This result is in agreement with
a scenario in which more massive galaxies formed at high redshift in the
highest peaks of the density field, while less massive objects form at later
epochs from the more general population of dark-matter halos.Comment: 13 pages, 10 figures, accepted in A&
The zCOSMOS 10k-Bright Spectroscopic Sample
We present spectroscopic redshifts of a large sample of galaxies with I_(AB) < 22.5 in the COSMOS field, measured from spectra of 10,644 objects that have been obtained in the first two years of observations in the zCOSMOS-bright redshift survey. These include a statistically complete subset of 10,109 objects. The average accuracy of individual redshifts is 110 km s^(â1), independent of redshift. The reliability of individual redshifts is described by a Confidence Class that has been empirically calibrated through repeat spectroscopic observations of over 600 galaxies. There is very good agreement between spectroscopic and photometric redshifts for the most secure Confidence Classes. For the less secure Confidence Classes, there is a good correspondence between the fraction of objects with a consistent photometric redshift and the spectroscopic repeatability, suggesting that the photometric redshifts can be used to indicate which of the less secure spectroscopic redshifts are likely right and which are probably wrong, and to give an indication of the nature of objects for which we failed to determine a redshift. Using this approach, we can construct a spectroscopic sample that is 99% reliable and which is 88% complete in the sample as a whole, and 95% complete in the redshift range 0.5 < z < 0.8. The luminosity and mass completeness levels of the zCOSMOS-bright sample of galaxies is also discussed
The VIMOS VLT Deep Survey. The Assembly History of the Stellar Mass in Galaxies: from the Young to the Old Universe
We present a detailed analysis of the Galaxy Stellar Mass Function of
galaxies up to z=2.5 as obtained from the VVDS. We estimate the stellar mass
from broad-band photometry using 2 different assumptions on the galaxy star
formation history and show that the addition of secondary bursts to a
continuous star formation history produces systematically higher (up to 40%)
stellar masses. At low redshift (z=0.2) we find a substantial population of
low-mass galaxies (<10^9 Msun) composed by faint blue galaxies (M_I-M_K=0.3).
In general the stellar mass function evolves slowly up to z=0.9 and more
significantly above this redshift. Conversely, a massive tail is present up to
z=2.5 and have extremely red colours (M_I-M_K=0.7-0.8). We find a decline with
redshift of the overall number density of galaxies for all masses (59+-5% for
M>10^8 Msun at z=1), and a mild mass-dependent average evolution
(`mass-downsizing'). In particular our data are consistent with mild/negligible
(6x10^10 Msun). For less
massive systems the no-evolution scenario is excluded. A large fraction (>=50%)
of massive galaxies have been already assembled and converted most of their gas
into stars at z=1, ruling out the `dry mergers' as the major mechanism of their
assembly history below z=1. This fraction decreases to 33% at z=2. Low-mass
systems have decreased continuously in number and mass density (by a factor up
to 4) from the present age to z=2, consistently with a prolonged mass assembly
also at z<1.Comment: 20 pages with 12 encapsulated figures. Version accepted by A&
The zCOSMOS Redshift Survey: the role of environment and stellar mass in shaping the rise of the morphology-density relation from z~1
For more than two decades we have known that galaxy morphological segregation
is present in the Local Universe. It is important to see how this relation
evolves with cosmic time. To investigate how galaxy assembly took place with
cosmic time, we explore the evolution of the morphology-density relation up to
redshift z~1 using about 10000 galaxies drawn from the zCOSMOS Galaxy Redshift
Survey. Taking advantage of accurate HST/ACS morphologies from the COSMOS
survey, of the well-characterised zCOSMOS 3D environment, and of a large sample
of galaxies with spectroscopic redshift, we want to study here the evolution of
the morphology-density relation up to z~1 and its dependence on galaxy
luminosity and stellar mass. The multi-wavelength coverage of the field also
allows a first study of the galaxy morphological segregation dependence on
colour. We further attempt to disentangle between processes that occurred early
in the history of the Universe or late in the life of galaxies. The zCOSMOS
field benefits of high-resolution imaging in the F814W filter from the Advanced
Camera for Survey (ACS). We use standard morphology classifiers, optimised for
being robust against band-shifting and surface brightness dimming, and a new,
objective, and automated method to convert morphological parameters into early,
spiral, and irregular types. We use about 10000 galaxies down to I_AB=22.5 with
a spectroscopic sampling rate of 33% to characterise the environment of
galaxies up to z~1 from the 100 kpc scales of galaxy groups up to the 100 Mpc
scales of the cosmic web. ABRIDGEDComment: 23 pages, 12 figures, accepted for publication in Astronomy and
Astrophysic
The Vimos VLT Deep Survey: Global properties of 20000 galaxies in the I_AB<=22.5 WIDE survey
The VVDS-Wide survey has been designed with the general aim of tracing the
large-scale distribution of galaxies at z~1 on comoving scales reaching
~100Mpc/h, while providing a good control of cosmic variance over areas as
large as a few square degrees. This is achieved by measuring redshifts with
VIMOS at the ESO VLT to a limiting magnitude I_AB=22.5, targeting four
independent fields with size up to 4 sq.deg. each. The whole survey covers 8.6
sq.deg., here we present the general properties of the current redshift sample.
This includes 32734 spectra in the four regions (19977 galaxies, 304 type I
AGNs, and 9913 stars), covering a total area of 6.1 sq.deg, with a sampling
rate of 22 to 24%. The redshift success rate is above 90% independently of
magnitude. It is the currently largest area coverage among redshift surveys
reaching z~1. We give the mean N(z) distribution averaged over 6.1 sq.deg.
Comparing galaxy densities from the four fields shows that in a redshift bin
Deltaz=0.1 at z~1 one still has factor-of-two variations over areas as large as
~0.25 sq.deg. This level of cosmic variance agrees with that obtained by
integrating the galaxy two-point correlation function estimated from the F22
field alone, and is also in fairly good statistical agreement with that
predicted by the Millennium mocks. The variance estimated over the survey
fields shows explicitly how clustering results from deep surveys of even ~1
sq.deg. size should be interpreted with caution. This paper accompanies the
public release of the first 18143 redshifts of the VVDS-Wide survey from the 4
sq.deg. contiguous area of the F22 field at RA=22h, publicly available at
http://cencosw.oamp.frComment: Accepted for publication on Astronomy & Astrophysic
The SWIRE-VVDS-CFHTLS surveys: stellar mass assembly over the last 10 Gyears. Evidence for a major build up of the red sequence between z=2 and z=1
(abridged abstract) We present an analysis of the stellar mass growth over
the last 10 Gyrs using a large 3.6 selected sample. We split our sample
into active (blue) and quiescent (red) galaxies. Our measurements of the K-LFs
and LD evolution support the idea that a large fraction of galaxies is already
assembled at . Based on the analysis of the evolution of the stellar
mass-to-light ratio (in K-band) for the spectroscopic sub-sample, we derive the
stellar mass density for the entire sample. We find that the global evolution
of the stellar mass density is well reproduced by the star formation rate
derived from UV dust corrected measurements. Over the last 8Gyrs, we observe
that the stellar mass density of the active population remains approximately
constant while it gradually increases for the quiescent population over the
same timescale. As a consequence, the growth of the stellar mass in the
quiescent population must be due to the shutoff of star formation in active
galaxies that migrate into the quiescent population. From to , we
observe a major build-up of the quiescent population with an increase by a
factor of 10 in stellar mass, suggesting that we are observing the epoch when
an increasing fraction of galaxies are ending their star formation activity and
start to build up the red sequence.Comment: Accepted to A&A with major changes. 1 table and 13 figure
Physical properties of galaxies and their evolution in the VIMOS VLT Deep Survey. I. The evolution of the mass-metallicity relation up to z~0.9
We derive the mass-metallicity relation of star-forming galaxies up to
, using data from the VIMOS VLT Deep Survey. Automatic measurement of
emission-line fluxes and equivalent widths have been performed on the full
spectroscopic sample. This sample is divided into two sub-samples depending on
the apparent magnitude selection: wide () and deep
). These two samples span two different ranges of stellar
masses. Emission-line galaxies have been separated into star-forming galaxies
and active galactic nuclei using emission line ratios. For the star-forming
galaxies the emission line ratios have also been used to estimate gas-phase
oxygen abundance, using empirical calibrations renormalized in order to give
consistent results at low and high redshifts. The stellar masses have been
estimated by fitting the whole spectral energy distributions with a set of
stellar population synthesis models. We assume at first order that the shape of
the mass-metallicity relation remains constant with redshift. Then we find a
stronger metallicity evolution in the wide sample as compared to the deep
sample. We thus conclude that the mass-metallicity relation is flatter at
higher redshift. The observed flattening of the mass-metallicity relation at
high redshift is analyzed as an evidence in favor of the open-closed model.Comment: 21 pages, revised version submitted to A&
The VIMOS VLT Deep Survey: Tracing the galaxy stellar mass assembly history over the last 8Gyr
We selected a mass-limited sample of 4048 objects from the VIMOS VLT Deep
Survey in the redshift interval 0.5<z<1.3. We used the amplitude of the 4000
Balmer break (Dn4000) to separate the galaxy population and the EW[OII]3727
line as proxy for the star formation activity. We discuss to what extent
stellar mass drives galaxy evolution, showing for the first time the interplay
between stellar ages and stellar masses over the past 8Gyr. Low-mass galaxies
have small Dn4000 and at increasing stellar mass, the galaxy distribution moves
to higher Dn4000 values as observed in the local Universe. As cosmic time goes
by, we witness an increasing abundance of massive spectroscopically ET systems
at the expense of the LT systems. This spectral transformation is a process
started at early epochs and continuing efficiently down to the local Universe.
This is confirmed by the evolution of our type-dependent stellar mass function.
The underlying stellar ages of LT galaxies apparently do not show evolution,
likely as a result of a continuous formation of new stars. All star formation
activity indicators consistently point towards a star formation history peaked
in the past for massive galaxies, with little or no residual star formation
taking place in the most recent epochs. The activity and efficiency of forming
stars are mechanisms that depend on stellar mass, and the mass assembly becomes
progressively less efficient in massive systems as time elapses. The concepts
of star formation downsizing and mass assembly downsizing describe a single
scenario that has a top-down evolutionary pattern. The role of (dry) merging
events seems to be only marginal at z<1.3, as our estimated efficiency in
stellar mass assembly can possibly account for the progressive accumulation of
passively evolving galaxies.Comment: Accepted for pubblication in A&A, 14 pages, 5 figure
The zCOSMOS Survey. The dependence of clustering on luminosity and stellar mass at z=0.2-1
We study the dependence of galaxy clustering on luminosity and stellar mass
at redshifts z ~ [0.2-1] using the first zCOSMOS 10K sample.
We measure the redshift-space correlation functions xi(rp,pi) and its
projection wp(rp) for sub-samples covering different luminosity, mass and
redshift ranges. We quantify in detail the observational selection biases and
we check our covariance and error estimate techniques using ensembles of
semi-analytic mock catalogues. We finally compare our measurements to the
cosmological model predictions from the mock surveys.
At odds with other measurements, we find a weak dependence of galaxy
clustering on luminosity in all redshift bins explored. A mild dependence on
stellar mass is instead observed. At z~0.7, wp(rp) shows strong excess power on
large scales. We interpret this as produced by large-scale structure dominating
the survey volume and extending preferentially in direction perpendicular to
the line-of-sight. We do not see any significant evolution with redshift of the
amplitude of clustering for bright and/or massive galaxies.
The clustering measured in the zCOSMOS data at 0.5<z<1 for galaxies with
log(M/M_\odot)>=10 is only marginally consistent with predictions from the mock
surveys. On scales larger than ~2 h^-1 Mpc, the observed clustering amplitude
is compatible only with ~1% of the mocks. Thus, if the power spectrum of matter
is LCDM with standard normalization and the bias has no unnatural
scale-dependence, this result indicates that COSMOS has picked up a
particularly rare, ~2-3 sigma positive fluctuation in a volume of ~10^6 h^-1
Mpc^3. These findings underline the need for larger surveys of the z~1 Universe
to appropriately characterize the level of structure at this epoch.Comment: 18 pages, 21 figures, accepted for publication in Astronomy and
Astrophysic
The UV luminosity function and star formation rate of the Coma cluster
We present estimates of the GALEX NUV and FUV luminosity functions (LFs) of
the Coma cluster, over a total area of ~9 deg^2 (~25 Mpc^2), i.e. from the
cluster center to the virial radius. Our analysis represents the widest and
deepest UV investigation of a nearby cluster of galaxies made to date. The Coma
UV LFs show a faint-end slope steeper than the one observed in the local field.
This difference, more evident in NUV, is entirely due to the contribution of
massive quiescent systems (e.g. ellipticals, lenticulars and passive spirals),
more frequent in high density environments. On the contrary, the shape of the
UV LFs for Coma star-forming galaxies does not appear to be significantly
different from that of the field, consistently with previous studies of local
and high redshift clusters. We demonstrate that such similarity is only a
selection effect, not providing any information on the role of the environment
on the star formation history of cluster galaxies. By integrating the UV LFs
for star-forming galaxies (corrected for the first time for internal dust
attenuation), we show that the specific star formation rate of Coma is
significantly lower than the integrated SSFR of the field and that Coma-like
clusters contribute only <7% of the total SFR density of the local universe.
Approximately 2/3 of the whole star-formation in Coma is occurring in galaxies
with M_star < 10^10 M_sol. The vast majority of star-forming galaxies has
likely just started its first dive into the cluster core and has not yet been
affected by the cluster environment. The total stellar mass accretion rate of
Coma is ~(0.6-1.8) x 10^12 M_sol Gyr^-1, suggesting that a significant fraction
of the population of lenticular and passive spirals observed today in Coma
could originate from infalling galaxies accreted between z~1 and z~0.Comment: Accepted for publication on MNRAS. 23 pages, 2 tables, 14 figure
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