1,249 research outputs found
The VIMOS VLT Deep Survey. The different assembly history of passive and star-forming L_B >= L*_B galaxies in the group environment at z < 1
We use the VIMOS VLT Deep Survey to study the close environment of galaxies
in groups at 0.2 = L*_B galaxies (Me_B =
M_B + 1.1z <= -20) are identified with Me_B <= -18.25 and within a relative
distance 5h^-1 kpc <= rp <= 100h^-1 kpc and relative velocity Delta v <= 500
km/s . The richness N of a group is defined as the number of Me_B <= -18.25
galaxies belonging to that group. We split our principal sample into red,
passive galaxies with NUV - r >= 4.25 and blue, star-forming galaxies with NUV
- r < 4.25. We find that blue galaxies with a close companion are primarily
located in poor groups, while the red ones are in rich groups. The number of
close neighbours per red galaxy increases with N, with n_red being proportional
to 0.11N, while that of blue galaxies does not depend on N and is roughly
constant. In addition, these trends are found to be independent of redshift,
and only the average n_blue evolves, decreasing with cosmic time. Our results
support the following assembly history of L_B >= L*_B galaxies in the group
environment: red, massive galaxies were formed in or accreted by the dark
matter halo of the group at early times (z >= 1), therefore their number of
neighbours provides a fossil record of the stellar mass assembly of groups,
traced by their richness N. On the other hand, blue, less massive galaxies have
recently been accreted by the group potential and are still in their parent
dark matter halo, having the same number of neighbours irrespective of N. As
time goes by, these blue galaxies settle in the group potential and turn red
and/or fainter, thus becoming satellite galaxies in the group. With a toy
quenching model, we estimate an infall rate of field galaxies into the group
environment of R_infall = 0.9 - 1.5 x 10^-4 Mpc^-3 Gyr^-1 at z ~ 0.7.Comment: Astronomy and Astrophysics, in press. 11 pages, 11 figures, 4 tables.
Minor changes with respect to the first versio
Comparison of the VIMOS-VLT Deep Survey with the Munich semi-analytical model. II. The colour-density relation up to z=1.5
[Abridged] We perform on galaxy mock catalogues the same colour-density
analysis made by Cucciati et al. (2006) on a 5 Mpc/h scale using the VVDS-Deep
survey, and compare the results from mocks with observed data. We use mocks
with the same flux limits (I=24) as the VVDS (CMOCKS), built using the semi-
analytic model by De Lucia & Blaizot (2007) applied to the Millennium
Simulation. From CMOCKS, we extracted samples of galaxies mimicking the VVDS
observational strategy (OMOCKS). We computed the B-band Luminosity Function LF
and the colour-density relation (CDR) in the mocks. We find that the LF in
mocks roughly agrees with the observed LF, but at z<0.8 the faint-end slope of
the model LF is steeper than the VVDS one. Computing the LF for early and late
type galaxies, we show that mocks have an excess of faint early-type and of
bright late-type galaxies with respect to data. We find that the CDR in OMOCKS
is in excellent agreement with the one in CMOCKS. At z~0.7, the CDR in mocks
agrees with the VVDS one (red galaxies reside mainly in high densities). Yet,
the strength of the CDR in mocks does not vary within 0.2<z<1.5, while the
observed relation flattens with increasing z and possibly inverts at z=1.3. We
argue that the lack of evolution in the CDR in mocks is not due only to
inaccurate prescriptions for satellite galaxies, but that also the treatment of
central galaxies has to be revised. The reversal of the CDR can be explained by
wet mergers between young galaxies, producing a starburst event. This should be
seen on group scales. A residual of this is found in observations at z=1.5 on
larger scales, but not in the mocks, suggesting that the treatment of physical
processes affecting satellites and central galaxies in models should be
revised.Comment: 15 pages, 12 figures, accepted for publication in A&
HeII emitters in the VIMOS VLT Deep Survey: PopIII star formation or peculiar stellar populations in galaxies at 2<z<4.6?
The aim of this work is to identify HeII emitters at 2<z<4.6 and to constrain
the source of the hard ionizing continuum that powers the HeII emission. We
have assembled a sample of 277 galaxies with a high quality spectroscopic
redshift at 2<z<4.6 from the VVDS survey, and we have identified 39 HeII1640A
emitters. We study their spectral properties, measuring the fluxes, equivalent
widths (EW) and FWHM for most relevant lines. About 10% of galaxies at z~3 show
HeII in emission, with rest frame equivalent widths EW0~1-7A, equally
distributed between galaxies with Lya in emission or in absorption. We find 11
high-quality HeII emitters with unresolved HeII line (FWHM_0<1200km/s), 13
high-quality emitters with broad He II emission (FWHM_0>1200km/s), 3 AGN, and
an additional 12 possible HeII emitters. The properties of the individual broad
emitters are in agreement with expectations from a W-R model. On the contrary,
the properties of the narrow emitters are not compatible with such model,
neither with predictions of gravitational cooling radiation produced by gas
accretion. Rather, we find that the EW of the narrow HeII line emitters are in
agreement with expectations for a PopIII star formation, if the episode of star
formation is continuous, and we calculate that a PopIII SFR of 0.1-10 Mo yr-1
only is enough to sustain the observed HeII flux. We conclude that narrow HeII
emitters are either powered by the ionizing flux from a stellar population rare
at z~0 but much more common at z~3, or by PopIII star formation. As proposed by
Tornatore et al. (2007), incomplete ISM mixing may leave some small pockets of
pristine gas at the periphery of galaxies from which PopIII may form, even down
to z~2 or lower. If this interpretation is correct, we measure at z~3 a SFRD in
PopIII stars of 10^6Mo yr^-1 Mpc^-3 qualitatively comparable to the value
predicted by Tornatore et al. (2007).Comment: accepted for publication in A&
The Vimos VLT Deep Survey: Stellar mass segregation and large-scale galaxy environment in the redshift range 0.2<z<1.4
Hierarchical models of galaxy formation predict that the properties of a dark
matter halo depend on the large-scale environment surrounding the halo. As a
result of this correlation, we expect massive haloes to be present in larger
number in overdense regions than in underdense ones. Given that a correlation
exists between a galaxy stellar mass and the hosting dark matter halo mass, the
segregation in dark matter halo mass should then result in a segregation in the
distribution of stellar mass in the galaxy population. In this work we study
the distribution of galaxy stellar mass and rest-frame optical color as a
function of the large-scale galaxy distribution using the VLT VIMOS Deep Survey
sample, in order to verify the presence of segregation in the properties of the
galaxy population. We use the VVDS redshift measurements and multi-band
photometric data to derive estimates of the stellar mass, rest-frame optical
color, and of the large-scale galaxy density, on a scale of approximately 8
Mpc, for a sample of 5619 galaxies in the redshift range 0.2<z<1.4. We observe
a significant mass and optical color segregation over the whole redshift
interval covered by our sample, such that the median value of the mass
distribution is larger and the rest-frame optical color is redder in regions of
high galaxy density. The amplitude of the mass segregation changes little with
redshift, at least in the high stellar mass regime that we can uniformely
sample over the 0.2<z<1.4 redshift interval. The color segregation, instead,
decreases significantly for z>0.7. However, when we consider only galaxies in
narrow bins of stellar mass, in order to exclude the effects of the stellar
mass segregation on the galaxy properties, we do not observe any more any
significant color segregation.Comment: 7 pages, 5 figures; accepted for publication in Astronomy and
Astrophysic
The 10k zCOSMOS: morphological transformation of galaxies in the group environment since z~1
We study the evolution of galaxies inside and outside of the group
environment since z=1 using a large well defined set of groups and galaxies
from the zCOSMOS-bright redshift survey in the COSMOS field. The fraction of
galaxies with early-type morphologies increases monotonically with M_B
luminosity and stellar mass and with cosmic epoch. It is higher in the groups
than elsewhere, especially at later epochs. The emerging environmental effect
is superposed on a strong global mass-driven evolution, and at z~0.5 and
log(M*/Msol)~10.2, the "effect" of group environment is equivalent to (only)
about 0.2 dex in stellar mass or 2 Gyr in time. The stellar mass function of
galaxies in groups is enriched in massive galaxies. We directly determine the
transformation rates from late to early morphologies, and for transformations
involving colour and star formation indicators. The transformation rates are
systematically about twice as high in the groups as outside, or up to 3-4 times
higher correcting for infall and the appearance of new groups. The rates reach
values, for masses around the crossing mass 10^10.5 Msol, as high as
(0.3-0.7)/Gyr in the groups, implying transformation timescales of 1.4-3 Gyr,
compared with less than 0.2/Gyr, i.e. timescales >5 Gyr, outside of groups. All
three transformation rates decrease at higher stellar masses, and must decrease
also at the lower masses below 10^10 Msol which we cannot well probe. The rates
involving colour and star formation are consistently higher than those for
morphology, by a factor of about 50%. Our conclusion is that the
transformations which drive the evolution of the overall galaxy population
since z~1 must occur at a rate 2-4 times higher in groups than outside of them.Comment: 21 pages, 13 figures, submitted to Ap
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 VIMOS VLT Deep Survey :Evolution of the major merger rate since z~1 from spectroscopicaly confirmed galaxy pairs
From the VIMOS VLT Deep Survey we use a sample of 6447 galaxies with I_{AB} <
24 to identify 251 pairs of galaxies, each member with a secure spectroscopic
redshift, which are close in both projected separation and in velocity. We find
that at z ~ 0.9, 10.9 +/- 3.2 % of galaxies with M_B(z) < -18-Qz are in pairs
with separations dr < 20 kpc/h, dv < 500 km/s, and with dM_B < 1.5,
significantly larger than 3.76 +/- 1.71 % at z ~ 0.5; we find that the pair
fraction evolves as (1+z)^m with m = 2.49 +/- 0.56. For brighter galaxies with
M_B(z=0) < -18.77, the pair fraction is higher and its evolution with redshift
is somewhat flatter with m=1.88 \pm 0.40, a property also observed for galaxies
with increasing stellar masses. Early type, dry mergers, pairs increase their
relative fraction from 3 % at z ~ 0.9 to 12 % at z ~ 0.5. We find that the
merger rate evolves as N_{mg}=(9.05 +/- 3.76) * 10^{-4}) * (1+z)^{2.43 +/-
0.76}. We find that the merger rate of galaxies with M_B(z) < -18-Qz has
significantly evolved since z ~ 1. The merger rate is increasing more rapidly
with redshift for galaxies with decreasing luminosities, indicating that the
flat evolution found for bright samples is not universal. The merger rate is
also strongly dependent on the spectral type of galaxies involved, late type
mergers being more frequent in the past, while early type mergers are more
frequent today, contributing to the rise in the local density of early type
galaxies. About 20 % of the stellar mass in present day galaxies with
log(M/M_{sun}) > 9.5 has been accreted through major merging events since z ~
1, indicating that major mergers have contributed significantly to the growth
in stellar mass density of bright galaxies over the last half of the life of
the Universe.Comment: 22 pages, 19 figures, accepted in A&
Structure detection in the D1 CFHTLS deep field using accurate photometric redshifts: a benchmark
We investigate structures in the D1 CFHTLS deep field in order to test the
method that will be applied to generate homogeneous samples of clusters and
groups of galaxies in order to constrain cosmology and detailed physics of
groups and clusters. Adaptive kernel technique is applied on galaxy catalogues.
This technique needs none of the usual a-priori assumptions (luminosity
function, density profile, colour of galaxies) made with other methods. Its
main drawback (decrease of efficiency with increasing background) is overcame
by the use of narrow slices in photometric redshift space. There are two main
concerns in structure detection. One is false detection and the second, the
evaluation of the selection function in particular if one wants "complete"
samples. We deal here with the first concern using random distributions. For
the second, comparison with detailed simulations is foreseen but we use here a
pragmatic approach with comparing our results to GalICS simulations to check
that our detection number is not totally at odds compared to cosmological
simulations. We use XMM-LSS survey and secured VVDS redshifts up to z~1 to
check individual detections. We show that our detection method is basically
capable to recover (in the regions in common) 100% of the C1 XMM-LSS X-ray
detections in the correct redshift range plus several other candidates.
Moreover when spectroscopic data are available, we confirm our detections, even
those without X-ray data.Comment: 14 pages, 22 additionnal jpeg figures, accepted in A&
NIR Follow-Up of the VVDS 02hr Field
We present a new K-band survey covering 623 arcmin in the VVDS 0226-0430
deep field down to a limiting magnitude K 20.5. We use the
spectroscopic sample extracted from this new K-band catalogue to assess the
effectiveness of optical-near infrared color selections in identifying extreme
classes of objects at high redshift.Comment: 6 pages, 4 figures. To appear in the Proceedings of the IAU Symposium
No. 235, 2006, "Galaxy Evolution across the Hubble Time", F. Combes & J.
Palous, ed
The VIMOS VLT Deep Survey final data release: a spectroscopic sample of 35016 galaxies and AGN out to z~6.7 selected with 17.5<=i_{AB}<=24.7
We describe the completed VIMOS VLT Deep Survey, and the final data release
of 35016 galaxies and type-I AGN with measured spectroscopic redshifts up to
redshift z~6.7, in areas 0.142 to 8.7 square degrees, and volumes from 0.5x10^6
to 2x10^7h^-3Mpc^3. We have selected samples of galaxies based solely on their
i-band magnitude reaching i_{AB}=24.75. Spectra have been obtained with VIMOS
on the ESO-VLT, integrating 0.75h, 4.5h and 18h for the Wide, Deep, and
Ultra-Deep nested surveys. A total of 1263 galaxies have been re-observed
independently within the VVDS, and from the VIPERS and MASSIV surveys. They are
used to establish the redshift measurements reliability, to assess
completeness, and to provide a weighting scheme taking into account the survey
selection function. We describe the main properties of the VVDS samples, and
the VVDS is compared to other spectroscopic surveys. In total we have obtained
spectroscopic redshifts for 34594 galaxies, 422 type-I AGN, and 12430 Galactic
stars. The survey has enabled to identify galaxies up to very high redshifts
with 4669 redshifts in 1<=z_{spec}<=2, 561 in 2<=z_{spec}<=3 and 468 with
z_{spec}>3, and specific populations like LAE have been identified out to
z=6.62. We show that the VVDS occupies a unique place in the parameter space
defined by area, depth, redshift coverage, and number of spectra. The VVDS
provides a comprehensive survey of the distant universe, covering all epochs
since z, or more than 12 Gyr of cosmic time, with a uniform selection, the
largest such sample to date. A wealth of science results derived from the VVDS
have shed new light on the evolution of galaxies and AGN, and their
distribution in space, over this large cosmic time. A final public release of
the complete VVDS spectroscopic redshift sample is available at
http://cesam.lam.fr/vvds.Comment: Submitted 30 June 2013, Accepted 22 August 2013. Updated with
published versio
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