234 research outputs found
Pervasive Artificial Intelligence in Next Generation Wireless: The Hexa-X Project Perspective
The VIRMOS-VLT Deep Survey
The aim of the VIRMOS VLT Deep Survey (VVDS) is to study of the evolution of
galaxies, large scale structures and AGNs from a sample of more than 150,000
galaxies with measured redshifts in the range 0<z<5+. The VVDS will rely on the
VIMOS and NIRMOS wide field multi-object spectrographs, which the VIRMOS
consortium is delivering to ESO. Together, they offer unprecedented multiplex
capability in the wavelength range 0.37-1.8microns, allowing for large surveys
to be carried out. The VVDS has several main aspects: (1) a deep multi-color
imaging survey over 18deg^2 of more than one million galaxies, (2) a "wide"
spectroscopic survey with more than 130,000 redshifts measured for objects
brighter than IAB=22.5 over 18deg^2, (3) a "deep" survey with 50,000 redshifts
measured to IAB=24, (4) ultra-deep" surveys with several thousand redshifts
measured to IAB=25, (5) multi-wavelength observations with the VLA and XMM.Comment: 5 pages including figures; to appear in Proc. of the ESO/ECF/STSCI
"Deep Fields" workshop, Garching Oct 2000, (Publ: Springer
The VIMOS-VLT Deep Survey - The evolution of galaxy clustering per spectral type to z~1.5
We measure the evolution of clustering for galaxies with different spectral
types from 6495 galaxies with 17.5<=I_AB<=24 and measured spectroscopic
redshift in the first epoch VIMOS-VLT Deep Survey. We classify our sample into
4 classes, based on the fit of well-defined galaxy spectral energy
distributions on observed multi-color data. We measure the projected function
wp(rp) and estimate the best-fit parameters for a power-law real-space
correlation function. We find the clustering of early-spectral-type galaxies to
be markedly stronger than that of late-type galaxies at all redshifts up to
z<=1.2. At z~0.8, early-type galaxies display a correlation length
r_0=4.8+/-0.9h^{-1}Mpc, while late types have r_0=2.5+/-0.4h^{-1}Mpc. The
clustering of these objects increases up to r_0=3.42+/-0.7h^{-1}Mpc for z~1.4.
The relative bias between early- and late-type galaxies within our
magnitude-limited survey remains approximately constant with b~1.7-1.8 from
z~=0.2 up to z~=1, with indications for a decrease at z>1.2, due to the growth
in clustering of the star-forming population. We find similar results when
splitting the sample into `red' and `blue' galaxies using the observed color
bi-modality. When compared to the expected linear growth of mass fluctuations,
a natural interpretation of these observations is that: (a) the assembly of
massive early type galaxies is already mostly complete in the densest dark
matter halos at z~=1; (b) luminous late-type galaxies are located in
higher-density, more clustered regions of the Universe at z~=1.5 than at
present, indicating that star formation activity is progressively increasing,
going back in time, in the higher-density peaks that today are mostly dominated
by old galaxies.Comment: 12 pages, Accepted on 11-Feb-06 for publication in Astronomy and
Astrophysic
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 VIRMOS-VLT Deep Survey: the last 10 billion years of evolution of galaxy clustering
We discuss the evolution of clustering of galaxies in the Universe from the
present epoch back to z ~ 2, using the first-epoch data from the VIMOS-VLT Deep
Survey (VVDS). We present the evolution of the projected two-point correlation
function of galaxies for the global galaxy population, as well as its
dependence on galaxy intrinsic luminosities and spectral types. While we do not
find strong variations of the correlation function parameters with redshift for
the global galaxy population, the clustering of objects with different
intrinsic luminosities evolved significantly during last 8-10 billion years.
Our findings indicate that bright galaxies in the past traced higher density
peaks than they do now and that the shape of the correlation function of most
luminous galaxies is different from observed for their local counterparts,
which is a supporting evidence of a non-trivial evolution of the galaxy vs.
dark matter bias.Comment: 4 pages, 4 figures, to appear in the proceedings of the conference
'At the Edge of the Universe' (9-13 October 2006, Sintra, Portugal
Testing gravity on large scales. The skewness of the galaxy distribution at z~1
We study the evolution of the low-order moments of the galaxy overdensity
distribution over the redshift interval 0.7<z<1.5. We find that the variance
and the normalized skewness evolve over this redshift interval in a way that is
remarkably consistent with predictions of first- and second-order perturbation
theory. This finding confirms the standard gravitational instability paradigm
over nearly 9 Gyrs of cosmic time and demonstrates the importance of accounting
for the non-linear component of galaxy biasing to avoid disagreement between
theory and observations.Comment: To appear in the proceedings of 43rd Rencontres de Moriond on
Cosmology (La Thuile, 2008
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&
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
Accurate photometric redshifts for the CFHT Legacy Survey calibrated using the VIMOS VLT Deep Survey
We present photometric redshifts for an uniquely large and deep sample of
522286 objects with i'_{AB}<25 in the Canada-France Legacy Survey ``Deep
Survey'' fields, which cover a total effective area of 3.2 deg^2. We use 3241
spectroscopic redshifts with 0<z<5 from the VIMOS VLT Deep Survey as a
calibration to derive these photometric redshifts. We devise a robust
calibration method which removes systematic trends in the photometric redshifts
and significantly reduces the fraction of catastrophic errors. We use our
unique spectroscopic sample to present a detailed assessment of the robustness
of the photometric redshift sample. For a sample selected at i'_{AB}<24, we
reach a redshift accuracy of \sigma_{\Delta z/(1+z)}=0.037 with \eta=3.7% of
catastrophic error. The reliability of our photometric redshifts is lower for
fainter objects: we find \sigma_{\Delta z/(1+z)}=0.029, 0.043 and \eta=1.7%,
5.4% for samples selected at i'_{AB}=17.5-22.5 and 22.5-24 respectively. We
find that the photometric redshifts of starburst galaxies in our sample are
less reliable: although these galaxies represent only 18% of the spectroscopic
sample they are responsible for 54% of the catastrophic errors. We find an
excellent agreement between the photometric and the VVDS spectroscopic redshift
distributions at i'_{AB}<24. Finally, we compare the redshift distributions of
i' selected galaxies on the four CFHTLS deep fields, showing that cosmic
variance is already present on fields of 0.8 deg^2.Comment: 19 pages, 17 figures, submitted to A&A. The photometric redshifts
described in this paper will be made publicly available from 1st may 2006 at
http://terapix.iap.fr and http://cencosw.oamp.fr
The VIMOS VLT Deep Survey: the faint type-1 AGN sample
We present the type-1 active galactic nuclei (AGN) sample extracted from the
VIMOS VLT Deep Survey first observations of 21000 spectra in 1.75 square
degree. This sample, which is purely magnitude limited, free of morphological
or color selection biases, contains 130 broad line AGN (BLAGN) spectra with
redshift up to 5. Our data are divided into a wide (Iab < 22.5) and a deep (Iab
< 24) subsample containing 56 and 74 objects respectively. Because of its depth
and selection criteria, this sample is uniquely suited to study the population
of faint type-1 AGN. Our measured surface density (~ 472 +- 48 BLAGN per square
degree with Iab < 24) is significantly higher than that of any other optically
selected sample of BLAGN with spectroscopic confirmation. By applying a
morphological and color analysis to our AGN sample we find that: (1)~23% of the
AGN brighter than Iab=22.5 are classified as extended; this percentage
increases to ~42% for those with z < 1.6; (2) a non-negligible fraction of our
BLAGN are lying close to the color space area occupied by stars in u*-g' versus
g'-r' color-color diagram. This leads us to the conclusion that classical
optical ultraviolet preselection technique, if employed at such deep magnitudes
(Iab=22.5) in conjuction with a preselection of point-like sources, can miss
miss up to ~35% of the AGN population. Finally, we present a composite spectrum
of our sample of objects. While the continuum shape is very similar to that of
the SDSS composite at short wavelengths, it is much redder than it at lambda >
3000 A. We interpret this as due to significant contamination from emission of
the host galaxies, as expected from the faint absolute magnitudes sampled by
our survey.Comment: Accepted to A&A, 18 pages, 14 figure
- âŠ