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Aims. An unbiased and detailed characterization of the galaxy luminosity function (LF) is a basic requirement in many astrophysical issues: it is of particular interest in assessing the role of the environment in the evolution of the LF of different galaxy types.

Context. Future dark energy space missions such as JDEM and EUCLID are being designed to survey the galaxy population to trace the geometry of the universe and the growth of structure, which both depend on the cosmological model. To reach the goal of high precision cosmology they need to evaluate the capabilities of different instrument designs based on realistic mock catalogs of the galaxy distribution.

Context. The COSMOS survey is a multiwavelength survey aimed to study the evolution of galaxies, AGN and large scale structures. Within this survey XMM-COSMOS a powerful tool to detect AGN and galaxy clusters. The XMM-COSMOS is a deep X-ray survey over the full 2 deg2of the COSMOS area. It consists of 55 XMM-Newtonpointings for a total exposure of ~1.5 Ms with an average vignetting-corrected depth of 40 ks across the field of view and a sky coverage of 2.13 deg2.

Aims. We investigate the relationships between three main optical galaxy observables (spectral properties, colors, and morphology), exploiting the data set provided by the COSMOS/zCOSMOS survey. The purpose of this paper is to define a simple galaxy classification cube, with a carefully selected sample of ≈1000 galaxies.

We present an analysis of the excitation conditions of the molecular gas in the streamers and the outflow of M 82 based on observations obtained at the IRAM 30 m telescope. Our analysis of $J=1{\to}0$and $J=2{\to}1$transitions of CO and 13CO and the CO($J=3{\to}2$) line in 13 regions outside the central starburst disk shows that the gas density within the streamer/outflow system is about an order of magnitude lower (2) than in the central molecular disk. We have used an LVG model and data from the literature to constrain the flux density in each CO transition (the “CO line SED”) arising from the streamer/outflow system and the central starburst disk itself. Globally, we find that the CO flux density up to the $J=3{\to}2$line is dominated by the diffuse outer regions while lines above the $J=5{\to}4$transition are almost exclusively emitted by the central starburst disk. We compare the CO line SED of M 82 to CO observations of galaxies at high redshift and suggest that small high-J/low-JCO flux density ratios (observed in some of these sources) are not necessarily caused by a different excitation of the central molecular gas concentration, but may result from an additional, more extended and diffuse gas reservoir around these systems, reminiscent of the situation in M 82.

We study the spatial clustering of 538 X-ray selected AGN in the 2?deg2XMM-COSMOS field that are spectroscopically identified with IAB<23 and span the redshift range z=0.2-3.0. The median redshift and X-ray luminosity of the sample are z = 0.98 and L0.5-10=6.3?1043?erg?s-1, respectively. A strong clustering signal is detected at ~18? level, which is the most significant measurement obtained to date for clustering of X-ray selected AGN. By fitting the projected correlation function w(rp) with a power law on scales of rp=0.3-40h-1?Mpc, we derive a best-fit comoving correlation length of r0= 8.6?0.5h-1?Mpc and slope of ?=1.88?0.07 (Poissonian errors; bootstrap errors are about a factor of?2?larger). An excess signal is observed in the range rp?5-15h-1?Mpc, which is due to a large-scale structure at z?0.36 containing about 40 AGN, a feature which is evident over many wavelengths in the COSMOS field. When removing the z?0.36 structure or computing w(rp) in a narrower range around the peak of the redshift distribution (e.g. z=0.4-1.6), the correlation length decreases to r0?5-6h-1?Mpc, which is consistent with what is observed for bright optical QSOs at the same redshift.?We investigate the clustering properties of obscured and unobscured AGN separately, adopting different definitions for the source obscuration. For the first time, we are able to provide a significant measurement for the spatial clustering of obscured AGN at z?1. Within the statistical uncertainties, we do not find evidence that AGN with broad optical lines (BLAGN) cluster differently from AGN without broad optical lines (non-BLAGN). Based on these results, which are limited by object statistics, however, obscured and unobscured AGN are consistent with inhabiting similar environments.?The evolution of AGN clustering with redshift is also investigated. No significant difference is found between the clustering properties of XMM-COSMOS AGN at redshifts below or above z=1.?The correlation length measured for XMM-COSMOS AGN at z?1 is similar to that of massive galaxies (stellar mass M*? 3?1010?M?) at the same redshift. This suggests that AGN at z?1 are preferentially hosted by massive galaxies, as observed both in the local and in the distant (z?2) Universe. According to a simple clustering evolution scenario, we find that the relics of AGN are expected to have a correlation length as large as r0?8h-1?Mpc by z=0, and hence to be hosted by local bright (L?L*) ellipticals.?We make use of dark matter halo catalogs from the Millennium simulation to determine the typical halo hosting moderately luminous z?1?AGN. We find that XMM-COSMOS AGN live in halos with masses M?2.5?1012M?h-1. By combining the number density of XMM-COSMOS AGN to that of the hosting dark matter halos we estimate the AGN duty cycle and lifetimes. We find lifetimes approximately of 1?Gyr for AGN at z?1, which are longer than those estimated for optically bright QSOs at the same redshift. These longer lifetimes mainly reflect the higher number density of AGN selected by X-ray samples.?

Aims.We explore the connection between black hole growth at the center of obscured quasars selected from the XMM-COSMOS survey and the physical properties of their host galaxies. We study a bolometric regime ( ⟨ Lbol⟩  = 8  ×  1045erg s-1) where several theoretical models invoke major galaxy mergers as the main fueling channel for black hole accretion.

Aims.Our goal is to develop a new and reliable statistical method to classify galaxies from large surveys. We probe the reliability of the method by comparing it with a three-dimensional classification cube, using the same set of spectral, photometric and morphological parameters.

Context.A substantial amount of the stellar mass growth across cosmic time occurred within dust-enshrouded environments. So far, identification of complete samples of distant star-forming galaxies from the short wavelength range has been strongly biased by the effect of dust extinction. Nevertheless, the exact amount of star-forming activity that took place in high-redshift dusty galaxies but that has currently been missed by optical surveys has barely been explored.

Context.Nearly 100 new strong-lens candidates have been discovered in the COSMOS field. Among these, 20 lens candidates with 0.34 ≲ zlens≲ 1.13 feature multiple images of background sources.

We study the impact of the environment on the evolution of galaxies in the zCOSMOS 10 k sample in the redshift range 0.1 ≤ z≤ 1.0 over an area of  ~1.5 deg2. The considered sample of secure spectroscopic redshifts contains about 8500 galaxies, with their stellar masses estimated by SED fitting of the multiwavelength optical to near-infrared (NIR) photometry. The evolution of the galaxy stellar mass function (GSMF) in high and low density regions provides a tool to study the mass assembly evolution in different environments; moreover, the contributions to the GSMF from different galaxy types, as defined by their SEDs and their morphologies, can be quantified. At redshift z~ 1, the GSMF is only slightly dependent on environment, but at lower redshifts the shapes of the GSMFs in high- and low-density environments become extremely different, with high density regions exhibiting a marked bimodality, not reproducible by a single Schechter function. As a result of this analysis, we infer that galaxy evolution depends on both the stellar mass and the environment, the latter setting the probability of a galaxy to have a given mass: all the galaxy properties related to the stellar mass show a dependence on environment, reflecting the difference observed in the mass functions. The shapes of the GSMFs of early- and late-type galaxies are almost identical for the extremes of the density contrast we consider, ranging from isolated galaxies to rich group members. The evolution toward z= 0 of the transition mass ℳcross, i.e., the mass at which the early- and late-type GSMFs match each other, is more rapid in high density environments, because of a difference in the evolution of the normalisation of GSMFs compared to the total one in the considered environment. The same result is found by studying the relative contributions of different galaxy types, implying that there is a more rapid evolution in overdense regions, in particular for intermediate stellar masses. The rate of evolution is different for sets of galaxy types divided on the basis of their SEDs or their morphologies, tentatively suggesting that the migration from the blue cloud to the red sequence occurs on a shorter timescale than the transformation from disc-like morphologies to ellipticals. Our analysis suggests that environmental mechanisms of galaxy transformation start to be more effective at z< 1. The comparison of the observed GSMFs to the same quantities derived from a set of mock catalogues based on semi-analytical models shows disagreement, in both low and high density environments: in particular, blue galaxies in sparse environments are overproduced in the semi-analytical models at intermediate and high masses, because of a deficit of star formation suppression, while at z< 0.5 an excess of red galaxies is present in dense environments at intermediate and low masses, because of the overquenching of satellites.

Aims. We present the analysis of the U− Vrest-frame color distribution and some spectral features as a function of mass and environment for a sample of early-type galaxies up to z= 1 extracted from the zCOSMOS spectroscopic survey. This analysis is used to place constraints on the relative importance of these two properties in controlling galaxy evolution. Methods. We used the zCOSMOS 10k-bright sample, limitedto the AB magnitude range 15 < I< 22.5, from which we extracted two different subsamples of early-type galaxies. The first sample (“red galaxies”) was selected using a photometric classification (2098 galaxies), while in the second case (“ETGs”) we combined morphological, photometric, and spectroscopic properties to obtain a more reliable sample of elliptical, red, passive, early-type galaxies (981 galaxies). The analysis is performed at fixed mass to search for any dependence of the color distribution on environment, and at fixed environment to search for any mass dependence. Results. In agreement with the low redshift results of the SDSS, we find that the color distribution of red galaxies is not strongly dependent on environment for all mass bins, exhibiting only a weak trend such that galaxies in overdense regions (log 10(1 + δ) ~ 1.2) are redder than galaxies in underdense regions (log 10(1 + δ) ~ 0.1), with a difference of ⟨Δ(U− V)rest⟩ = 0.027 ± 0.008 mag. On the other hand, the dependence on mass is far more significant, and we find that the average colors of massive galaxies (log 10(M/M⊙) ~ 10.8) are redder by ⟨Δ(U− V)rest⟩ = 0.093 ± 0.007 mag than low-mass galaxies (log 10(M/M⊙) ~ 10) throughout the entire redshift range. We study the color-mass (U− V)rest∝ SM·log 10(M/M⊙) relation, finding a mean slope ⟨SM⟩ = 0.12 ± 0.005, while the color-environment (U− V)rest∝ Sδ·log 10(1 + δ) relation is flatter, with a slope always smaller than Sδ≈ 0.04. The spectral analysis that we perform on our ETGs sample is in good agreement with our photometric results: we study the 4000 Å break and the equivalent width of the HδBalmer line, finding for D4000 a dependence on mass (⟨ΔD4000⟩ = 0.11 ± 0.02 between log 10(M/M⊙) ~ 10.2 and log 10(M/M⊙) ~ 10.8), and a much weaker dependence on environment (⟨ΔD4000⟩ = 0.05 ± 0.02 between high and low environment quartiles). The same is true for the equivalent width of Hδ, for which we measure a difference of ΔEW0(Hδ) = 0.28 ± 0.08 Å across the same mass range and no significant dependence on environment. By analyzing the lookback time of early-type galaxies, we support the possibility of a downsizing scenario, in which massive galaxies with a stronger D4000 and an almost constant equivalent width of Hδformed their mass at higher redshift than lower mass ones. We also conclude that the main driver of galaxy evolution is the galaxy mass, the environment playing a subdominant role.

Aims.With the first  ~10 000 spectra of the flux limited zCOSMOS sample (IAB≤ 22.5) we want to study the evolution of environmental effects on galaxy properties since z~ 1.0, and to disentangle the dependence among galaxy colour, stellar mass and local density.

We present the galaxy stellar mass function (GSMF) to redshift z≃ 1, based on the analysis of about 8500 galaxies with I< 22.5 (AB mag) over 1.4 deg2, which are part of the zCOSMOS-bright 10k spectroscopic sample. We investigate the total GSMF, as well as the contributions of early- and late-type galaxies (ETGs and LTGs, respectively), defined by different criteria (broad-band spectral energy distribution, morphology, spectral properties, or star formation activities). We unveil a galaxybimodality in the global GSMF, whose shape is more accurately represented by 2 Schechter functions, one linked to the ETG and the other to the LTG populations. For the global population, we confirm a mass-dependent evolution (“mass-assembly downsizing”), i.e., galaxy number density increases with cosmic time by a factor of two between z= 1 and z= 0 for intermediate-to-low mass (log (ℳ/ℳ⊙)  ~ 10.5) galaxies but less than 15% for log (ℳ/ℳ⊙)  >  11. We find that the GSMFevolution at intermediate-to-low values of ℳ (log (ℳ/ℳ⊙)  < 10.6) is mostly explained by the growth in stellar mass driven by smoothly decreasing star formation activities, despite the redder colours predicted in particular at low redshift. The low residual evolution is consistent, on average, with  ~0.16 merger per galaxy per Gyr (of which fewer than 0.1 are major), with a hint of a decrease with cosmic time but not a clear dependence on the mass. From the analysis of different galaxy types, we find that ETGs, regardless of the classification method, increase in number density with cosmic time more rapidly with decreasing ℳ, i.e., follow a top-down building history, with a median “building redshift” increasing with mass (z> 1 for log (ℳ/ℳ⊙)  >  11), in contrast to hierarchical model predictions. For LTGs, we find that the number density of blue or spiral galaxies with log (ℳ/ℳ⊙)  >  10 remains almost constant with cosmic time from z~1. Instead, the most extreme population of star-forming galaxies (with high specific star formation), at intermediate/high-mass, rapidly decreases in number density with cosmic time. Our data can be interpreted as a combination of different effects. Firstly, we suggest a transformation, driven mainly by SFH, from blue, active, spiral galaxies of intermediate mass to blue quiescent and subsequently (1−2 Gyr after) red, passive types of low specific star formation. We find an indication that the complete morphological transformation, probably driven by dynamical processes, into red spheroidal galaxies, occurred on longer timescales or followed after 1−2 Gyr. A continuous replacement of blue galaxies is expected to be accomplished by low-mass active spirals increasing their stellar mass. We estimate the growth rate in number and mass density of the red galaxies at different redshifts and masses. The corresponding fraction of blue galaxies that, at any given time, is transforming into red galaxies per Gyr, due to the quenching of their SFR, is on average  ~25% for log (ℳ/ℳ⊙)  <  11. We conclude that the build-up of galaxies and in particular of ETGs follows the same downsizing trend with mass (i.e. occurs earlier for high-mass galaxies) as the formation of their stars and follows the converse of the trend predicted by current SAMs. In this scenario, we expect there to be a negligible evolution of the galaxy baryonic mass function (GBMF) for the global population at all masses and a decrease with cosmic time in the GBMFfor the blue galaxy population at intermediate-high masses.

Context. Using Chandra observations we identified a sample of seven off-nuclear X-ray sources in the redshift range z= 0.072–0.283, located within optically bright galaxies in the COSMOS Survey. All of them, if associated with their closest bright galaxy, would have L[0.5–7 keV] >1039erg s-1and therefore can be classified as ultraluminous X-ray sources (ULXs). Aims. Using the multi-wavelength coverage available in the COSMOS field, we studied the properties of the host galaxies of these ULXs. In detail, we derived their star formation rate from Hαmeasurements and their stellar masses using SED fitting techniques with the aim to compute the probability to have an off-nuclear source based on the host galaxy properties. We divided the host galaxies in different morphological classes with the available ACS/HST imaging.Methods. We selected off-nuclear candidates with the following criteria: 1) the distance between the X-ray and the optical centroid has to be larger than 0.9´´, larger than 1.8 times the radius of the Chandra positional error circle and smaller than the Petrosian radius of the host galaxy; 2) the optical counterpart is a bright galaxy (RAB<22); 3) the redshift of the counterpart is lower than z= 0.3; 4) the source has been observed in at least one Chandra pointing at an off-axis angle smaller than 5´; 5) the X-ray positional error is smaller than 0.8´´. We verified each candidate super-imposing the X-ray contours on the optical/IR images. We expect less than one misidentified AGN due to astrometric errors and on average 1.3 serendipitous background source matches.Results. We find that our ULXs candidates are located in regions of the SFR versus ${\rm M}_\star$plane where one or more off-nuclear detectable sources are expected. From a morphological analysis of the ACS imaging and the use of rest-frame colours, we find that our ULXs are hosted both in late and early type galaxies. Finally, we find that the fraction of galaxies hosting a ULX ranges from ≈0.5% to ≈0.2% going from $L_{0.5{-}2~{\rm keV}}$= 3 × 1039erg s-1to $L_{0.5{-}2~{\rm keV}}$= 2 × 1040erg s-1.

Aims. The identities of the main processes triggering and quenching star-formation in galaxies remain unclear. A key stage in evolution, however, appears to be represented by post-starburst galaxies. To investigate the prevalence of these galaxies and their impact on galaxy evolution in general, we initiated a multiwavelength study of galaxies with k+aspectral features in the well-studied COSMOS field.Methods. We examine a mass-selected sample of k+agalaxies in the COSMOS field at z= 0.48-1.2 using the spectroscopic zCOSMOS sample. To classify galaxies in their k+aphase, we use a spectroscopic criterion, based on the amplitude of the Hdabsorption line and the absence of the [OII] emission line. We develop our analysis for a well-defined sample by imposing stringent confidence levels on the spectroscopic redshifts and spectral measurements. We compare our results for two mass-selected samples of star-forming and quiescent galaxies selected using a purely spectral classification scheme from the 10?000 zCOSMOS catalogue (i.e.?, based on measurements of 4000 Å break and EW[OII]).Results. In our mass-limited sample, k+agalaxies occupy the brightest tail of the luminosity distribution. They are as massive as quiescent galaxies and populate the green valley in the colour versus luminosity (or stellar mass) distribution. A small percentage (<8%) of these galaxies have radio and/or X-ray counterparts (implying an upper limit to the SFR of ~8  $\cal M_\odot$?yr-1). Over the entire redshift range explored, the class of post-starburst galaxies is morphologically a heterogeneous population with a similar incidence of bulge-dominated and disky galaxies. This distribution does not vary with the strength of the Hdabsorption line but instead with stellar mass in a way reminiscent of the well-known mass-morphology relation. The results about the incidence of asymmetries and the concentration of the light distribution derived from HST/ACS images imply that this galaxy population possibly represents an intermediate stage of galaxy evolution. Although k+agalaxies are also found in underdense regions, they appear to reside typically in a similarly rich environment as quiescent galaxies on a physical scale of ~2–8 Mpc, and in groups they show a morphological early-to-late type ratio similar to the quiescent galaxy class. With the current data set, we do not find evidence of statistical significant evolution in either the number/mass density of k+agalaxies at intermediate redshift with respect to the local values, or the spectral properties, although more solid results on this and other aspects will be obtained following the completion of the survey.Conclusions. Several mechanisms related and unrelated to the environment are at work in quenching star-formation activity in galaxies on short timescales (<1 Gyr). Those galaxies, which are affected by a sudden quenching of their star-formation activity, may increase the stellar mass of the red-sequence by up to a non-negligible level of ~10%.

Context. Groups of galaxies are a common environment, bridging the gap between starforming field galaxies and quiescent cluster galaxies. Within groups secular processes could be at play, contributing to the observed strong decrease of star formation with cosmic time in the global galaxy population.Aims. We took advantage of the wealth of information provided by the first ~10?000 galaxies of the zCOSMOS-bright survey and its group catalogue to study in detail the complex interplay between group environment and galaxy properties. Methods. The classical indicator $F_{\rm blue}$, i.e., the fraction of blue galaxies, proved to be a simple but powerful diagnostic tool. We studied its variation for different luminosity and mass selected galaxy samples, divided as to define groups/field/isolated galaxy subsamples.Results. Using rest-frame evolving B-band volume-limited samples, the groups galaxy population exhibits significant blueing as redshift increases, but maintains a systematic difference (a lower $F_{\rm blue}$) with respect to the global galaxy population, and an even larger difference with respect to the isolated galaxy population. However moving to mass selected samples it becomes apparent that such differences are largely due to the biased view imposed by the B-band luminosity selection, being driven by the population of lower mass, bright blue galaxies for which we miss the redder, equally low mass, counterparts. By carefully focusing the analysis on narrow mass bins such that mass segregation becomes negligible we find that only for the lowest mass bin explored, i.e., $\log ({\cal M}_{*}/{\cal M}_{\odot}) \leq 10.6 $, does a significant residual difference in color remain as a function of environment, while this difference becomes negligible toward higher masses.Conclusions. Our results indicate that red galaxies of mass $\log ({\cal M}_{*}/{\cal M}_{\odot}) \geq 10.8$are already in place at z~ 1 and do not exhibit any strong environmental dependence, possibly originating from so-called nature or internal mechanisms. In contrast, for lower galaxy masses and redshifts lower than z~ 1, we observe the emergence in groups of a population of nurture red galaxies: slightly deviating from the trend of the downsizing scenario followed by the global galaxy population, and more so with cosmic time. These galaxies exhibit signatures of group-related secular physical mechanisms directly influencing galaxy evolution. Our analysis implies that these mechanisms begin to significantly influence galaxy evolution after z~ 1, a redshift corresponding to the emergence of structures in which these mechanisms take place.