We present a detailed analysis of the Galaxy Stellar Mass Function (GSMF) of galaxies up to z =2.5 as obtained from the VIMOS VLT Deep Survey (VVDS). Our survey offers the possibility to investigate ...the GSMF using two different samples: (1) an optical ( I-selected 17.5 <I_{\rm AB}<24) main spectroscopic sample of about 6500 galaxies over 1750 arcmin super(2) and (2) a near-IR ( K-selected K_{\rm AB}<22.34 similar to {\rm and} similar to K_{\rm AB}<22.84) sample of about 10 200 galaxies, with photometric redshifts accurately calibrated on the VVDS spectroscopic sample, over 610 arcmin super(2). We apply and compare two different methods to estimate the stellar mass {\cal M}_{\rm stars} from broad-band photometry based on different assumptions about the galaxy star-formation history. We find that the accuracy of the photometric stellar mass is satisfactory overall, and show that the addition of secondary bursts to a continuous star formation history produces systematically higher (up to 40%) stellar masses. We derive the cosmic evolution of the GSMF, the galaxy number density and the stellar mass density in different mass ranges. At low redshift ( z\simeq0.2) we find a substantial population of low-mass galaxies (<10 { similar to M_\odot) composed of faint blue galaxies ( M_I-M_K \simeq 0.3). In general the stellar mass function evolves slowly up to z\sim0.9 and more rapidly above this redshift, in particular for low mass systems. Conversely, a massive population is present up to z =2.5 and has extremely red colours ( M_I-M_K\simeq 0.7-0.8). We find a decline with redshift of the overall number density of galaxies for all masses (59\pm5% for 10 proportional to similar to M_\odot$--> {\cal M}_{\rm stars} > 10 proportional to similar to M_\odot at z =1), and a mild mass-dependent average evolution ("mass-downsizing"). In particular our data are consistent with mild/negligible (<30%) evolution up to z\sim0.7 for massive galaxies ( }6\times10 6M_\odot$--> {>}6\times10 6M_\odot). For less massive systems the no-evolution scenario is excluded. Specifically, a large fraction ({\ge}50\%) of massive galaxies have been assembled and converted most of their gas into stars at z\sim1, ruling out "dry mergers" as the major mechanism of their assembly history below z\simeq1. This fraction decreases to {\sim}33\% at z\sim2. Low-mass systems have decreased continuously in number density (by a factor of up to 4.1\pm0.9) from the present age to z =2, consistent with a prolonged mass assembly also at z <1. The evolution of the stellar mass density is relatively slow with redshift, with a decrease of a factor of 2.3\pm0.1 at z =1 and about 4.5\pm0.3 at z =2.5.
Aims. The aim of this work is to study the contribution of the Lyα emitters to the star formation rate density (SFRD) of the Universe in the interval 2 < z < 6.6. Methods. We assembled a sample of ...217 Lyα emitters (LAE) from the Vimos-VLT Deep Survey (VVDS) with secure spectroscopic redshifts in the redshift range 2 < z < 6.62 and fluxes down to F ~ 1.5 × 10-18 erg/s/cm2. Of those Lyα emitters, 133 are serendipitous identifications in the 22 arcmin2 total slit area surveyed with the VVDS-Deep and the 3.3 arcmin2 from the VVDS Ultra-Deep survey, and 84 are targeted identifications in the 0.62 deg2 surveyed with the VVDS-DEEP and 0.16 deg2 from the Ultra-Deep survey. Among the serendipitous targets we estimate that 90% of the emission lines are most probably Lyα, while the remaining 10% could be either OII3727 or Lyα. We computed the luminosity function (LF) and derived the star-formation rate density using this sample of LAE. Results. The VVDS-LAE sample reaches faint line fluxes F(Lyα) = 1.5 × 10-18 erg/s/cm2 (corresponding to L(Lyα) ~ 1041 erg/s at z ~ 3), allows the faint-end slope of the luminosity function to be constrained to α ~ −1.6 ± 0.12 at redshift z ~ 2.5 and to \hbox{$\alpha\sim-1.78^{0.10}_{-0.12}$}α~−1.78-0.120.10 at redshift ~4, placing trends found in previous LAE studies on firm statistical grounds, and indicating that sub-L ∗ LAE (LLy − α ≲ 1042.5 erg/s) contribute significantly to the SFRD. The projected number density and volume density of faint LAE in 2 ≤ z ≤ 6.6 with F > 1.5 × 10-18 erg/s/cm2 are 33 galaxies/arcmin2 and ~4 × 10-2 Mpc-3, respectively. We find that the observed luminosity function (LF) of LAEs does not evolve from z = 2 to z = 6. This implies that, after correction for the redshift-dependent IGM absorption, the intrinsic luminosity function must have evolved significantly over 3 Gyr. The SFRD from LAE contributes around 20% of the SFRD at z = 2−3, while the LAE appear to be the dominant source of star formation producing ionizing photons in the early universe z ~ > 5−6, equivalent to Lyman Break galaxies.
We have conducted a two-layered spectroscopic survey (1′ × 1′ ultra deep and 3′ × 3′ deep regions) in the Hubble Ultra Deep Field (HUDF) with the Multi Unit Spectroscopic Explorer (MUSE). The ...combination of a large field of view, high sensitivity, and wide wavelength coverage provides an order of magnitude improvement in spectroscopically confirmed redshifts in the HUDF; i.e., 1206 secure spectroscopic redshifts for Hubble Space Telescope (HST) continuum selected objects, which corresponds to 15% of the total (7904). The redshift distribution extends well beyond z> 3 and to HST/F775W magnitudes as faint as ≈ 30 mag (AB, 1σ). In addition, 132 secure redshifts were obtained for sources with no HST counterparts that were discovered in the MUSE data cubes by a blind search for emission-line features. In total, we present 1338 high quality redshifts, which is a factor of eight increase compared with the previously known spectroscopic redshifts in the same field. We assessed redshifts mainly with the spectral features O ii at z< 1.5 (473 objects) and Lyα at 2.9 <z< 6.7 (692 objects). With respect to F775W magnitude, a 50% completeness is reached at 26.5 mag for ultra deep and 25.5 mag for deep fields, and the completeness remains ≳ 20% up to 28–29 mag and ≈ 27 mag, respectively. We used the determined redshifts to test continuum color selection (dropout) diagrams of high-z galaxies. The selection condition for F336W dropouts successfully captures ≈ 80% of the targeted z ~ 2.7 galaxies. However, for higher redshift selections (F435W, F606W, and F775W dropouts), the success rates decrease to ≈ 20–40%. We empirically redefine the selection boundaries to make an attempt to improve them to ≈ 60%. The revised boundaries allow bluer colors that capture Lyα emitters with high Lyα equivalent widths falling in the broadbands used for the color-color selection. Along with this paper, we release the redshift and line flux catalog.
We use the current sample of ~10,000 zCOSMOS spectra of sources selected with I AB < 22.5 to define the density field out to z ~ 1, with much greater resolution in the radial dimension than has been ...possible with either photometric redshifts or weak lensing. We present the new algorithm that we have developed (ZADE) to incorporate objects not yet observed spectroscopically by modifying their photometric redshift probability distributions using the spectroscopic redshifts of nearby galaxies. We present a number of tests on mock catalogs used to justify this approach. The ZADE algorithm allows us to probe a broader range of galaxy environments and reduce the Poisson noise in the density field. The reconstructed overdensity field of the 10k zCOSMOS galaxies consists of cluster-like patterns surrounded by void-like regions, extending up to z ~ 1. Some of these structures are very large, spanning the ~50 h -1 Mpc transverse direction of the COSMOS field and extending up to Delta *Dz ~ 0.05 in redshift. We present the three-dimensional overdensity maps and compare the reconstructed overdensity field to the independently identified virialized groups of galaxies and clusters detected in the visible and in X-rays. The distribution of the overdense structures is in general well traced by these virialized structures. A comparison of the large-scale structures in the zCOSMOS data and in the mock catalogs reveals an excellent agreement between the fractions of the volume enclosed in structures of all sizes above a given overdensity between the data and the mocks in 0.2 < z < 1, although in the data these overdense regions are in generally larger contiguous structures.
Context. XMM and Chandra opened a new area for the study of clusters of galaxies not only for cluster physics, but also for the detection of faint and distant clusters that were inaccessible with ...previous missions. Aims. This article presents 66 spectroscopically confirmed clusters (0.05 ≤ z ≤ 1.5) within an area of 6 deg2 enclosed in the XMM-LSS survey. Almost two thirds have been confirmed with dedicated spectroscopy only and 10% have been confirmed with dedicated spectroscopy supplemented by literature redshifts. Methods. Sub-samples, or classes, of extended-sources are defined in a two-dimensional X-ray parameter space allowing for various degrees of completeness and contamination. We describe the procedure developed to assess the reality of these cluster candidates using the CFHTLS photometric data and spectroscopic information from our own follow-up campaigns. Results. Most of these objects are low-mass clusters, hence constituting a still poorly studied population. In a second step, we quantify the correlations between the optical properties such as richness or velocity dispersion and the cluster X-ray luminosities. We examine the relation of the clusters to the cosmic web. Finally, we review peculiar compact structures in the surveyed area such as very distant clusters and fossil groups.
We present a galaxy group catalog spanning the redshift range 0.1 z 1 in the ~ 1.7 deg2 COSMOS field, based on the first ~10,000 zCOSMOS spectra. The performance of both the Friends-of-Friends (FOF) ...and Voronoi-Delaunay method (VDM) approaches to group identification has been extensively explored and compared using realistic mock catalogs. We find that the performance improves substantially if groups are found by progressively optimizing the group-finding parameters for successively smaller groups, and that the highest fidelity catalog, in terms of completeness and purity, is obtained by combining the independently created FOF and VDM catalogs. The final completeness and purity of this catalog, both in terms of the groups and of individual members, compares favorably with recent results in the literature. The current group catalog contains 102 groups with N >= 5 spectroscopically confirmed members, with a further ~700 groups with 2 <= N <= 4. Most of the groups can be assigned a velocity dispersion and a dark-matter mass derived from the mock catalogs, with quantifiable uncertainties. The fraction of zCOSMOS galaxies in groups is about 25% at low redshift and decreases toward ~15% at z ~ 0.8. The zCOSMOS group catalog is broadly consistent with that expected from the semianalytic evolution model underlying the mock catalogs. Not least, we show that the number density of groups with a given intrinsic richness increases from redshift z ~ 0.8 to the present, consistent with the hierarchical growth of structure.
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.
We measure the stellar mass function (SMF) and stellar mass density of galaxies in the COSMOS field up to z ~ 6. We select them in the near-IR bands of the COSMOS2015 catalogue, which includes ...ultra-deep photometry from UltraVISTA-DR2, SPLASH, and Subaru/Hyper Suprime-Cam. At z> 2.5 we use new precise photometric redshifts with error σz = 0.03(1 + z) and an outlier fraction of 12%, estimated by means of the unique spectroscopic sample of COSMOS (~100 000 spectroscopic measurements in total, more than one thousand having robust zspec> 2.5). The increased exposure time in the DR2, along with our panchromatic detection strategy, allow us to improve the completeness at high z with respect to previous UltraVISTA catalogues (e.g. our sample is >75% complete at 1010 ℳ⊙ and z = 5). We also identify passive galaxies through a robust colour–colour selection, extending their SMF estimate up to z = 4. Our work provides a comprehensive view of galaxy-stellar-mass assembly between z = 0.1 and 6, for the first time using consistent estimates across the entire redshift range. We fit these measurements with a Schechter function, correcting for Eddington bias. We compare the SMF fit with the halo mass function predicted from ΛCDM simulations, finding that at z> 3 both functions decline with a similar slope in thehigh-mass end. This feature could be explained assuming that mechanisms quenching star formation in massive haloes become less effective at high redshifts; however further work needs to be done to confirm this scenario. Concerning the SMF low-mass end, it shows a progressive steepening as it moves towards higher redshifts, with α decreasing from -1.47+0.02-0.02 at z ≃ 0.1 to -2.11+0.30-0.13 at z ≃ 5. This slope depends on the characterisation of the observational uncertainties, which is crucial to properly remove the Eddington bias. We show that there is currently no consensus on the method to quantify such errors: different error models result in different best-fit Schechter parameters.
In a companion paper (Arnouts et al. 2004) we presented new measurements of the galaxy luminosity function at 1500 Angstroms out to z~1 using GALEX-VVDS observations (1039 galaxies with NUV<24.5 and ...z>0.2) and at higher z using existing data sets. In this paper we use the same sample to study evolution of the FUV luminosity density. We detect evolution consistent with a (1+z)^{2.5+/-0.7} rise to z~1 and (1+z)^{0.5+/-0.4} for z>1. The luminosity density from the most UV-luminous galaxies (UVLG) is undergoing dramatic evolution (x30) between 025%) of the total FUV luminosity density at z<1. We measure dust attenuation and star formation rates of our sample galaxies and determine the star formation rate density as a function of redshift, both uncorrected and corrected for dust. We find good agreement with other measures of the SFR density in the rest ultraviolet and Halpha given the still significant uncertainties in the attenuation correction.
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