We investigate the redshift and luminosity evolution of the galaxy colour-density relation using the data from the First Epoch VIMOS-VLT Deep Survey (VVDS). The size (6582 galaxies with good quality ...redshifts), depth ($I_{AB}\leq 24$) and redshift sampling rate (20% on the mean) of the survey enable us to reconstruct the 3D galaxy environment on relatively local scales ($R=5$$\,h^{-1}$ Mpc) up to redshift $z \sim 1.5$. Particular attention has been devoted to calibrate a density reconstruction scheme, which factors out survey selection effects and reproduces in an unbiased way the underlying “real” galaxy environment. We find that the colour-density relation shows a dramatic change as a function of cosmic time. While at lower redshift we confirm the existence of a steep colour-density relation, with the fraction of the reddest(/bluest) galaxies of the same luminosity increasing(/decreasing) as a function of density, this trend progressively disappears in the highest redshift bins investigated. Our results suggest the existence of an epoch (more remote for brighter galaxies) characterized by the absence of the colour-density relation on the $R=5$$\,h^{-1}$ Mpc scales investigated. The rest frame $u^{*}-g'$ colour–magnitude diagram shows a bimodal pattern in both low and high density environments up to redshift $z\sim 1.5$. We find that the bimodal distribution is not universal but strongly depends upon environment: at lower redshifts the colour–magnitude diagrams in low and high density regions are significantly different while the progressive weakening of the colour-density relation causes the two bimodal distributions to nearly mirror each other in the highest redshift bin investigated. Both the colour-density and the colour–magnitude-density relations, on the $R=5$$\,h^{-1}$ Mpc scales, appear to be a transient, cumulative product of genetic and environmental factors that have been operating over at least a period of 9 Gyr. These findings support an evolutionary scenario in which star formation/gas depletion processes are accelerated in more luminous objects and in high density environments: star formation activity is progressively shifting with cosmic time towards lower luminosity galaxies (downsizing), and out of high density environments.
Aims. We apply photometric redshift techniques to an investigation of the Coma cluster galaxy luminosity function (GLF) at faint magnitudes, in particular in the u* band where basically no studies ...are presently available at these magnitudes. Methods. Cluster members were selected based on probability distribution function from photometric redshift calculations applied to deep u*, B, V, R, I images covering a region of almost 1 deg2 (completeness limit R ~ 24). In the area covered only by the u* image, the GLF was also derived after a statistical background subtraction. Results. Global and local GLFs in the B, V, R, and I bands obtained with photometric redshift selection are consistent with our previous results based on a statistical background subtraction. The GLF in the u* band shows an increase in the faint end slope towards the outer regions of the cluster. The analysis of the multicolor type spatial distribution reveals that late type galaxies are distributed in clumps in the cluster outskirts, where X-ray substructures are also detected and where the GLF in the u* band is steeper. Conclusions. We can reproduce the GLFs computed with classical statistical subtraction methods by applying a photometric redshift technique. The u* GLF slope is steeper in the cluster outskirts, varying from α ~ -1 in the cluster center to α ~ -2 in the cluster periphery. The concentrations of faint late type galaxies in the cluster outskirts could explain these very steep slopes, assuming a short burst of star formation in these galaxies when entering the cluster.
We measure the evolution of clustering for galaxies with different spectral types from 6495 galaxies with 17.5 less than or equal to I sub(AB) less than or equal to 24 and measured spectroscopic ...redshifts in the first epoch VIMOS-VLT Deep Survey (VVDS). We divide our sample into four classes, based on the fit of well-defined galaxy spectral energy distributions on observed multi-color data. We measure the projected correlation function w sub(p)(r sub(p)) and estimate the best-fit parameters for a power-law real-space correlation function xi (r) = (r/r sub(o)) super(- gamma ). 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 similar to 0.8, early-type galaxies display a correlation length r sub(0) = 4.8 plus or minus 0.9 h super(-1) Mpc, while late types have r sub(0) = 2.5 plus or minus 0.4 h super(-1) Mpc. For the latest class of star-forming blue galaxies, we are able to push our clustering measurement to an effective redshift z similar to 1.4, for luminous galaxies (M sub(B)(AB) -21). The clustering of these objects increases up to r sub(0) = 3.42 plus or minus 0.7 h super(-1) Mpc for z = 1.2,2.0. The relative bias between early- and late-type galaxies within our magnitude-limited survey remains approximately constant with b = 1.6 plus or minus 0.3 from z = 0 to z = 1.2. This result is in agrement with the local findings and fairly robust against different way of classifying red and blue galaxies. 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 their local low luminous counterpart, 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.
VIMOS (Visible Multi‐Object Spectrograph) is a multiobject imaging spectrograph installed at the VLT (Very large Telescope) at the ESO (European Southern Observatory) Paranal Observatory that is ...especially suited for survey work. VIMOS is characterized by its very high multiplexing factor: it is possible to take up to 800 spectra with 10
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long slits in a single exposure. To fully exploit its multiplexing potential, we designed and implemented a dedicated software tool: the VIMOS Mask Preparation Software (VMMPS), which allows the astronomer to select the objects to be spectroscopically observed, and provides for automatic slit positioning and slit number maximization within the instrumental constraints. The output of VMMPS is used to manufacture the slit masks to be mounted in the instrument for spectroscopic observations.
We present the first measurements of the Probability Distribution Function (PDF) of galaxy fluctuations in the four-passes, first-epoch VIMOS-VLT Deep Survey (VVDS) cone, covering 0.4x0.4 deg between ...0.4 < z < 1.5. We show that the PDF of density contrasts of the VVDS galaxies is an unbiased tracer of the underlying parent distribution up to redshift z = 1.5, on scales R = 8 and 10 h-1 Mpc. The second moment of the PDF, i.e., the rms fluctuations of the galaxy density field, is to a good approximation constant over the full redshift baseline investigated: we find that, in redshift space, s8 for galaxies brighter than McB = -20 + 5 log h has a mean value of 0.94 c 0.07 in the redshift interval 0.7 < z < 1.5. The third moment, i.e., the skewness, increases with cosmic time: we find that the probability of having underdense regions is greater at z 6 0.7 than it was at z 6 1.5. By comparing the PDF of galaxy density contrasts with the theoretically predicted PDF of mass fluctuations we infer the redshift-, density- and scale-dependence of the biasing function b(z,d,R) between galaxy and matter overdensities up to redshift z = 1.5. Our results can be summarized as follows: i) the galaxy bias is an increasing function of redshift: evolution is marginal up to z 6 0.8 and more pronounced for z QQQ ? 0.8; ii) the formation of bright galaxies is inhibited below a characteristic mass-overdensity threshold whose amplitude increases with redshift and luminosity; iii) the biasing function is non linear in all the redshift bins investigated with non-linear effects of the order of a few to 610% on scales > 5 h-1 Mpc. By subdividing the sample according to galaxy luminosity and colors, we also show that: iv) brighter galaxies are more strongly biased than less luminous ones at every redshift and the dependence of biasing on luminosity at z 6 0.8 is in good agreement with what is observed in the local Universe; v) red objects are systematically more biased than blue objects at all cosmic epochs investigated, but the relative bias between red and blue objects is constant as a function of redshift in the interval 0.7 < z < 1.5, and its value (brel 6 1.4) is similar to what is found at z 6 0.
In this paper we present a new deep, wide-field near-infrared imaging survey. Our J- and K-band observations in four separate fields (0226-04, 2217+00, 1003+02, 1400+05) complement optical BVRI, ...ultraviolet and spectroscopic observations undertaken as part of the VIMOS-VLT deep survey (VVDS). In total, our survey spans 6400 arcmin2. Our catalogues are reliable in all fields to at least K 6 20.75 and J 6 21.50 (defined as the magnitude where object contamination is less than 10% and completeness greater than 90%). Taken together these four fields represents a unique combination of depth, wavelength coverage and area. Most importantly, our survey regions span a broad range of right ascension and declination which allow us to make a robust estimate of the effects of cosmic variance. We describe the complete data reduction process from raw observations to the construction of source lists and outline a comprehensive series of tests carried out to characterise the reliability of the final catalogues. From simulations we determine the completeness function of each final stacked image, and estimate the fraction of spurious sources in each magnitude bin. We compare the statistical properties of our catalogues with literature compilations. We find that our J- and K-selected galaxy counts are in good agreement with previously published works, as are our (J - K) versus K colour-magnitude diagrams. Stellar number counts extracted from our fields are consistent with a synthetic model of our galaxy. Using the location of the stellar locus in colour-magnitude space and the measured field-to-field variation in galaxy number counts we demonstrate that the absolute accuracy of our photometric calibration is at the 5% level or better. Finally, an investigation of the angular clustering of K-selected extended sources in our survey displays the expected scaling behaviour with limiting magnitude, with amplitudes in each magnitude bin in broad agreement with literature values. In summary, these catalogues will be an excellent tool to investigate the properties of near-infrared selected galaxies, and such investigations will be the subject of several articles currently in preparation.
Aims. We present a measurement of the dependence of galaxy clustering on galaxy stellar mass at redshift z\sim0.9, based on the first-epoch data from the VVDS-Deep survey. Methods. Concentrating on ...the redshift interval 0.5< z <1.2, we measured the projected correlation function, w_{\rm p}(r_{\rm p}), within mass-selected sub-samples covering the range similar to 10 super(9) and similar to 10 similar to M_\odot. We explored and quantify in detail the observational selection biases due to the flux-limited nature of the survey, both from the data themselves and with a suite of realistic mock samples constructed by coupling the Millennium Simulation to semi-analytic models. We identify the range of masses within which our main conclusions are robust against these effects. Serious incompleteness in mass is present below log\,(M/M_\odot) =9.5, with about two thirds of the galaxies in the range 9<\log\,(M/M_\odot) <9.5 that are lost due to their low luminosity and high mass-to-light ratio. However, the sample is expected to be 100% complete in mass above log\,(M/M_\odot) =10. Results. We present the first direct evidence for a dependence of clustering on the galaxy stellar mass at a redshift as high as z\sim0.85. We quantify this by fitting the projected function w_{\rm p}(r_{\rm p}) with a power-law model. The clustering length increases from r sub(0) =2.76 sub(-0.15) super(+0.17) h super(-1) Mpc for galaxies with mass 10 {9} similar to M_\odot$--> M>10 {9} similar to M_\odot to r sub(0) =4.28 sub(-0.45) super(+0.43) h super(-1) Mpc when only the most massive (10 similar to M_\odot$--> M>10 similar to M_\odot) are considered. At the same time, we observe a significant increase in the slope, which over the same range of masses, changes from gamma=1.67_to gamma=2.28_. Comparison to the SDSS measurements at z\sim0.15 shows that the evolution of w_{\rm p}(r_{\rm p}) is significant for samples of galaxies with M<10 similar to M_\odot, while it is negligible for more massive objects. Considering the growth of structure, this implies that the linear bias b_{\rm L} of the most massive galaxies evolves more rapidly between these two cosmic epochs. We quantify this effect by computing the value of b_{\rm L} from the SDSS and VVDS clustering amplitudes and find that b_{\rm L} decreases from 1.5\pm0.2 at z\sim0.85 to 1.33\pm0.03 at z\sim0.15, for the most massive galaxies, while it remains virtually constant (b_{\rm L}\sim1.3) for the remaining population. Qualitatively, this is the kind of scenario expected for the clustering of dark-matter halos as a function of their total mass and redshift. Our result therefore seems to indicate that galaxies with the highest stellar mass today were originally central objects of the most massive dark-matter halos at earlier times, whose distribution was strongly biased with respect to the overall mass density field.
Aims. In this paper we discuss the mix of star-forming and passive galaxies up to z similar to 2, based on the first epoch VIMOS-VLT Deep Survey (VVDS) data. Methods. We compute rest-frame magnitudes ...and colors and analyse the color-magnitude relation and the color distributions. We also use the multi-band VVDS photometric data and spectral templates fitting to derive multi-color galaxy types. Using our spectroscopic dataset we separate galaxies based on a star-formation activity indicator derived combining the equivalent width of the OII emission line and the strength of the D sub( )n(4000) continuum break. Results. In agreement with previous works we find that the global galaxy rest-frame color distribution follows a bimodal distribution at z \le 1, and we establish that this bimodality holds up to at least z =1.5. The details of the rest-frame color distribution depend however on redshift and on galaxy luminosity, with faint galaxies being bluer than the luminous ones over the whole redshift range covered by our data, and with galaxies becoming bluer as redshift increases. This latter blueing trend does not depend, to a first approximation, on galaxy luminosity. The comparison between the spectral classification and the rest-frame colors shows that about 35-40% of the red objects are in fact star forming galaxies. Hence we conclude that the red sequence cannot be used to effectively isolate a sample of purely passively evolving objects within a cosmological survey. We show how multi-color galaxy types have a slightly higher efficiency than rest-frame color in isolating the passive, non star- forming galaxies within the VVDS sample. Connected to these results is also the finding that the color-magnitude relations derived for the color and for the spectroscopically selected early-type galaxies have remarkably similar properties, with the contaminating star-forming galaxies within the red sequence objects introducing no significant offset in the rest frame colors. Therefore the average color of the red objects does not appear to be a very sensitive indicator for measuring the evolution of the early-type galaxy population.
With the new generation of spectrographs, integral field spectroscopy is becoming a widely used observational technique. The Integral Field Unit (IFU) of the Visible Multi–Object Spectrograph (VIMOS) ...on the ESO VLT allows sampling of a field as large as
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, covered by 6400 fibers coupled with microlenses. We present here the methods of the data‐processing software that has been developed to extract the astrophysical signal of faint sources from the VIMOS IFU observations. We focus on the treatment of the fiber‐to‐fiber relative transmission and the sky subtraction, and the dedicated tasks we have built to address the peculiarities and unprecedented complexity of the data set. We review the automated process we have developed under the VIPGI data organization and reduction environment (Scodeggio et al.2005), along with the quality control performed to validate the process. The VIPGI IFU data‐processing environment has been available to the scientific community to process VIMOS IFU data since 2003 November.
This paper presents the evolution of the clustering of the main population of galaxies from z 2 to z = 0.2, from the first epoch VIMOS VLT Deep Survey (VVDS), a magnitude limited sample with 17.5 ...less than or equal to I sub(AB) less than or equal to 24. The sample allows a direct estimate of evolution from within the same survey over the time base sampled. We have computed the correlation functions xi (r sub(p), pi ) and w sub(p)(r sub(p)), and the correlation length r sub(0)(z), for the VVDS-02h and VVDS-CDFS fields, for a total of 7155 galaxies in a 0.61 deg super(2) area. We find that the correlation length in this sample slightly increases from z = 0.5 to z = 1.1, with r sub(0)(z) = 2.2-2.9 h super(-1) Mpc (comoving), for galaxies comparable in luminosity to the local 2dFGRS and SDSS samples, indicating that the amplitude of the correlation function was 2.5 times lower at z 1 than observed locally. The correlation length in our lowest redshift bin z = 0.2, 0.5 is r sub(0) = 2.2 h super(-1) Mpc, lower than for any other population at the same redshift, indicating the low clustering of very low luminosity galaxies, 1.5 mag fainter than in the 2dFGRS or SDSS. The correlation length increases to r sub(0) similar to 3.6 h super(-1) Mpc at higher redshifts z = 1.3, 2.1, as we are observing increasingly brighter galaxies, comparable to galaxies with M sub(BsubAB) = -20.5 locally. We compare our measurement to the DEEP2 measurements in the range z = 0.7, 1.35 and find comparable results when applying the same magnitude and color selection criteria as in their survey. The slowly varying clustering of VVDS galaxies as redshift increases is markedly different from the predicted evolution of the clustering of dark matter, indicating that bright galaxies traced higher density peaks when the large scale structures were emerging from the dark matter distribution 9-10 billion years ago, being supporting evidence for a strong evolution of the galaxy vs. dark matter bias.
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