Papers by Marco Scodeggio
We present a galaxy group catalogue spanning the redshift range 0.1 z 1 in the ∼ 1.7 deg 2 COSMOS... more We present a galaxy group catalogue spanning the redshift range 0.1 z 1 in the ∼ 1.7 deg 2 COSMOS field, based on the first ∼ 10, 000 zCOSMOS spectra. The performance of both the Friendsof-Friends (FOF) and Voronoi-Delaunay-Method (VDM) approaches to group identification has been extensively explored and compared using realistic mock catalogues. 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 catalogue, in terms of completeness and purity, is obtained by combining the independently created FOF and VDM catalogues. The final completeness and purity of this catalogue, both in terms of the groups and of individual members, compares favorably with recent results in the literature. The current group catalogue 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 catalogues, 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 catalogue is broadly consistent with that expected from the semi-analytic evolution model underlying the mock catalogues. 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.
The Astrophysical Journal, 2010
We report the final optical identifications of the medium-depth (∼ 60 ksec), contiguous (2 deg 2)... more We report the final optical identifications of the medium-depth (∼ 60 ksec), contiguous (2 deg 2) XMM-Newton survey of the COSMOS field. XMM-Newton has detected ∼ 1800 X-ray sources down to limiting fluxes of ∼ 5 × 10 −16 , ∼ 3×10 −15 , and ∼ 7×10 −15 erg cm −2 s −1 in the 0.5-2 keV, 2-10 keV and 5-10 keV bands, respectively (∼ 1 × 10 −15 , ∼ 6 × 10 −15 , and ∼ 1 × 10 −14 erg cm −2 s −1 , in the three bands, respectively, over 50% of the area). The work is complemented by an extensive collection of multi-wavelength data from 24µm to UV, available from the COSMOS survey, for each of the X-ray sources, including spectroscopic redshifts for ∼ > 50% of the sample, and high-quality photometric redshifts for the rest. The XMM and multiwavelength flux limits are well matched: 1760 (98%) of the X-ray sources have optical counterparts, 1711 (∼ 95%) have IRAC counterparts, and 1394 (∼ 78%) have MIPS 24 µm detections. Thanks to the redshift completeness (almost 100%) we were able to constrain the high-luminosity tail of the X-ray luminosity function confirming that the peak of the number density of logL X > 44.5 AGN is at z∼ 2. Spectroscopically-identified obscured and unobscured AGN, as well as normal and starforming galaxies, present well-defined optical and infrared properties. We devised a robust method to identify a sample of ∼ 150 high redshift (z> 1), obscured AGN candidates for which optical spectroscopy is not available. We were able to determine that the fraction of the obscured AGN population at the highest (L X > 10 44 erg s −1) X-ray luminosity is ∼ 15 −30% when selection effects are taken into account, providing an important observational constraint for X-ray background synthesis. We studied in detail the optical spectrum and the overall spectral energy distribution of a prototypical Type 2 QSO, caught in a stage transitioning from being starburst dominated to AGN dominated, which was possible to isolate only thanks to the combination of X-ray and infrared observations.
The Astrophysical Journal, 2009
We present a study of the host galaxies of AGN selected from the zCOSMOS survey to establish if a... more We present a study of the host galaxies of AGN selected from the zCOSMOS survey to establish if accretion onto Supermassive Black Holes (SMBHs) and star formation are explicitly linked up to z ∼ 1. We identify 152 galaxies that harbor AGN, based on their X-ray emission (L 0.5−10 keV > 10 42 erg s −1) detected by XM M −N ewton observations of 7543 galaxies (i acs < 22.5). Star formation rates (SFRs), including those weighted by stellar mass, of a subsample are determined using the [OII]λ3727 emissionline luminosity, corrected for an AGN contribution based on the observed [OIII]λ5007 strength or that inferred by their hard (2-10 keV) X-ray luminosity. We find that an overwhelming majority of AGN host galaxies have significant levels of star formation with a distribution spanning ∼ 1 − 100 M ⊙ yr −1 ; their average SFR is higher than that of galaxies with equivalent stellar mass (M * > 4 × 10 10 M ⊙). The close association between AGN activity and star formation is further substantiated by an increase in the fraction of galaxies hosting AGN with the youthfulness of their stars as indicated by the rest-frame color (U-V) and spectral index D n (4000); we demonstrate that a mass-selected sample is required to alleviate an artifical peak in the AGN fraction falling in the transition region due to the fact that many 'blue cloud' galaxies have low mass-to-light ratios in luminosity-limited samples. We also find that the SFRs of AGN hosts evolve with cosmic time in a manner that closely mirrors the overall galaxy population and naturally explains the low SFRs in AGNs (z < 0.3) from the SDSS. We conclude that the conditions most conducive for AGN activity are a massive host galaxy and a large reservoir of gas. Furthermore, a direct correlation between mass accretion rate onto SMBHs and SFR is shown to be weak although the average ratio (∼ 10 −2) is constant with redshift, effectively shifting the evidence for a co-evolution scenario in a statistical manner to smaller physical scales (i.e., within the same galaxies). The order-of-magnitude increase in this ratio compared to the locally measured value of M BH /M bulge , is consistent with an AGN lifetime substantially shorter than that of star formation. Our findings illustrate an intermittent scenario with underlying complexities regarding fueling over vastly different physical (and temporal) scales yet to be firmly determined.
The Astrophysical Journal, 2010
We study the evolution of galaxies inside and outside of the group environment since z = 1 using ... more We study the evolution of galaxies inside and outside of the group environment since z = 1 using a large welldefined 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 * /M) ∼ 10.2, the "effect" of the 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 color and star formation indicators. The transformation rates are systematically about twice as high in the groups as outside, or up to three to four times higher correcting for infall and the appearance of new groups. The rates reach values as high as 0.3-0.7 Gyr −1 in the groups (for masses around the crossing mass 10 10.5 M), implying transformation timescales of 1.4-3 Gyr, compared with less than 0.2 Gyr −1 , i.e., timescales >5 Gyr, outside of groups. All three transformation rates decrease at higher stellar masses, and must also decrease at lower masses below 10 10 M which we cannot probe well. The rates involving color and star formation are consistently higher than those for morphology, by a factor of about 50%. Our conclusion is that the transformations that drive the evolution of the overall galaxy population since z ∼ 1 must occur at a rate two to four times higher in groups than outside of them.
The Astrophysical Journal, 2009
The impact of environment on AGN activity up to z ∼ 1 is assessed by utilizing a mass-selected sa... more The impact of environment on AGN activity up to z ∼ 1 is assessed by utilizing a mass-selected sample of galaxies from the 10k catalog of the zCOSMOS spectroscopic redshift survey. We identify 147 AGN by their X-ray emission as detected by XM M-Newton from a parent sample of 7234 galaxies. We measure the fraction of galaxies with stellar mass M * > 2.5 × 10 10 M ⊙ that host an AGN as a function of local overdensity using the 5th, 10th and 20th nearest neighbors that cover a range of physical scales (∼ 1 − 4 Mpc). Overall, we find that AGNs prefer to reside in environments equivalent to massive galaxies with substantial levels of star formation. Specifically, AGNs with host masses between 0.25 − 1 × 10 11 M ⊙ span the full range of environments (i.e., field-to-group) exhibited by galaxies of the same mass and rest-frame color or specific star formation rate. Host galaxies having M * > 10 11 M ⊙ clearly illustrate the association with star formation since they are predominantly bluer than the underlying galaxy population and exhibit a preference for lower density regions analogous to SDSS studies of narrow-line AGN. To probe the environment on smaller physical scales, we determine the fraction of galaxies (M * > 2.5 × 10 10 M ⊙) hosting AGNs inside optically-selected groups, and find no significant difference with field galaxies. We interpret our results as evidence that AGN activity requires a sufficient fuel supply; the probability of a massive galaxy to have retained some sufficient amount of gas, as evidence by its ongoing star formation, is higher in underdense regions where disruptive processes (i.e., galaxy harrassment, tidal stripping) are lessened.
Publications of the Astronomical Society of Japan, 2012
We present a photometric and spectroscopic study of galaxies at 0.5 < z < 1 as a function of the ... more We present a photometric and spectroscopic study of galaxies at 0.5 < z < 1 as a function of the environment based on data from the zCOSMOS survey. There is a fair amount of evidence that galaxy properties depend on the mass of groups and clusters, in the sense that quiescent galaxies prefer more massive systems. We base our analysis on a mass-selected environment using X-ray groups of galaxies, and define the group membership using a large number of spectroscopic redshifts from zCOSMOS. We show that the fraction of red galaxies is higher in groups than in the field at all redshifts probed in our study. Interestingly, the fraction of [O II] emitters on the red sequence increases at higher redshifts in groups, while the fraction does not strongly evolve in the field. This is due to increased dusty star-formation activities and/or increased activities of active galactic nuclei (AGNs) in highredshift groups. We investigate these possibilities using the 30-band photometry and X-ray data. We find that the stellar population of the red [O II] emitters in groups is old, and there is no clear hint of dusty star-formation activities in those galaxies. The observed increase of red [O II] emitters in groups is likely due to increased AGN activities. However, since our overall statistics are poor, any firm conclusions need to be drawn from a larger statistical sample of z 1 groups.
Il Nuovo Cimento B, 2007
Redshift-space distortions as a probe of dark energy by Liesbeth-Helena Gouws
Monthly Notices of the Royal Astronomical Society, 2011
We measure the spatial clustering of galaxies as a function of their morphological type at z 0.8,... more We measure the spatial clustering of galaxies as a function of their morphological type at z 0.8, for the first time in a deep redshift survey with full morphological information. This is obtained by combining high-resolution HST imaging and VLT spectroscopy for about 8, 500 galaxies to I AB = 22.5 with accurate spectroscopic redshifts from the zCOSMOS-Bright redshift survey. At this epoch, early-type galaxies already show a significantly stronger clustering than late-type galaxies on all probed scales. A comparison to the SDSS at z 0.1, shows that the relative clustering strength between early and late morphological classes tends to increase with cosmic time at small separations, while on large scales it shows no significant evolution since z 0.8. This suggests that most early-type galaxies had already formed in intermediate and dense environments at this epoch. Our results are consistent with a picture in which the relative clustering of different morphological types between z 1 and z 0, reflects the evolving role of environment in the morphological transformation of galaxies, on top of the global mass-driven evolution.
Monthly Notices of the Royal Astronomical Society, 2010
We investigate how the shape of the galaxy two-point correlation function as measured in the zCOS... more We investigate how the shape of the galaxy two-point correlation function as measured in the zCOSMOS survey depends on local environment, quantified in terms of the density contrast on scales of 5 h −1 Mpc. We show that the flat shape previously observed at redshifts between z = 0.6 and z = 1 can be explained by this volume being simply 10% over-abundant in high-density environments, with respect to a Universal density probability distribution function. When galaxies corresponding to the top 10% tail of the distribution are excluded, the measured w p (r p) steepens and becomes indistinguishable from ΛCDM predictions on all scales. This is the same effect recognised by Abbas & Sheth in the SDSS data at z 0 and explained as a natural consequence of halo-environment correlations in a hierarchical scenario. Galaxies living in high-density regions trace dark matter halos with typically higher masses, which are more correlated. If the density probability distribution function of the sample is particularly rich in high-density regions because of the variance introduced by its finite size,
Monthly Notices of the Royal Astronomical Society, 2013
Herschel is an ESA space observatory with science instruments provided by European-led Principal ... more Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
The Astrophysical Journal Supplement Series, 2007
zCOSMOS is a large redshift survey that is being undertaken in the COSMOS field using 600 hours o... more zCOSMOS is a large redshift survey that is being undertaken in the COSMOS field using 600 hours of observation with the VIMOS spectrograph on the 8-m VLT. The survey is designed to characterise the environments of COSMOS galaxies from the 100 kpc scales of galaxy groups up to the 100 Mpc scale of the cosmic web and to produce diagnostic information on galaxies and active galactic nuclei. The zCOSMOS survey consists of two parts: (a) zCOSMOS-bright, a magnitude-limited I-band I AB < 22.5 sample of about 20,000 galaxies with 0.1 < z < 1.2 covering the whole 1.7 deg 2 COSMOS ACS field, for which the survey parameters at z ~ 0.7 are designed to be directly comparable to those of the 2dFGRS at z ~ 0.1; and (b) zCOSMOS-deep, a survey of approximately 10,000 galaxies selected through colourselection criteria to have 1.4 < z < 3.0, within the central 1 deg 2. This paper describes the survey design and the construction of the target catalogues, and briefly outlines the observational program and the data pipeline. In the first observing season, spectra of 1303 zCOSMOS-bright targets and of 977 zCOSMOS-deep targets have been obtained. These are briefly analysed to demonstrate the characteristics that may be expected from zCOSMOS, and particularly zCOSMOS-bright, when it is finally completed between 2008-2009. The power of combining spectroscopic and photometric redshifts is demonstrated, especially in correctly identifying the emission line in single-line spectra and in determining which of the less reliable spectroscopic redshifts are correct and which are incorrect. These techniques bring the overall success rate in the zCOSMOS-bright so far to almost 90% and to above 97% in the 0.5 < z < 0.8 redshift range. Our zCOSMOS-deep spectra demonstrate the power of our selection techniques to isolate high redshift galaxies at 1.4 < z < 3.0 and of VIMOS to measure their redshifts using ultraviolet absorption lines.
Astronomy & Astrophysics, 2009
Aims. We want to derive the mass-metallicity relation of star-forming galaxies up to z ∼ 0.9, usi... more Aims. We want to derive the mass-metallicity relation of star-forming galaxies up to z ∼ 0.9, using data from the VIMOS VLT Deep Survey. The mass-metallicity relation is commonly understood as the relation between the stellar mass and the gas-phase oxygen abundance. Methods. Automatic measurement of emission-line fluxes and equivalent widths have been performed on the full spectroscopic sample of the VIMOS VLT Deep Survey. This sample is divided into two sub-samples depending on the apparent magnitude selection: wide (I AB < 22.5) and deep (I AB < 24). These two samples span two different ranges of stellar masses. Emission-line galaxies have been separated into star-forming galaxies and active galactic nuclei using emission line ratios. For the star-forming galaxies the emission line ratios have also been used to estimate gas-phase oxygen abundance, using empirical calibrations renormalized in order to give consistent results at low and high redshifts. The stellar masses have been estimated by fitting the whole spectral energy distributions with a set of stellar population synthesis models. Results. We assume at first order that the shape of the mass-metallicity relation remains constant with redshift. Then we find a stronger metallicity evolution in the wide sample as compared to the deep sample. We thus conclude that the mass-metallicity relation is flatter at higher redshift. At z ∼ 0.77, galaxies at 10 9.4 solar masses have −0.18 dex lower metallicities than galaxies of similar masses in the local universe, while galaxies at 10 10.2 solar masses have −0.28 dex lower metallicities. By comparing the mass-metallicity and luminosity-metallicity relations, we also find an evolution in mass-to-light ratio: galaxies at higher redshifts being more active. The observed flattening of the mass-metallicity relation at high redshift is analyzed as evidence in favor of the open-closed model.
Astronomy and Astrophysics, 2010
Context. Using Chandra observations we identified a sample of seven off-nuclear X-ray sources in ... more 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] > 10 39 erg s −1 and 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 Hα measurements 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 (R AB < 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 superimposing 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 M 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 keV = 3 × 10 39 erg s −1 to L 0.5−2 keV = 2 × 10 40 erg s −1 .
Astronomy and Astrophysics, 2005
In this paper we present the optical and near-infrared identifications of the 1054 radio sources ... more In this paper we present the optical and near-infrared identifications of the 1054 radio sources detected in the 20 cm deep radio survey down to a 5σ flux limit of ∼80 µJy obtained with the VLA in the VIMOS VLT Deep Survey VVDS-02h deep field.
Astronomy & Astrophysics, 2010
Aims. With the first ∼10000 spectra of the flux limited zCOSMOS sample (I AB ≤ 22.5) we want to s... more Aims. With the first ∼10000 spectra of the flux limited zCOSMOS sample (I AB ≤ 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. Methods. We use our previously derived 3D local density contrast δ, computed with the 5 th nearest neighbour approach, to study the evolution with z of the environmental effects on galaxy U-B colour, D4000Å break and [OII]λ3727 equivalent width (EW[OII]). We also analyze the implications due to the use of different galaxy selections, using luminosity or stellar mass, and we disentangle the relations among colour, stellar mass and δ studying the colour-density relation in narrow mass bins. Results. We confirm that within a luminosity-limited sample (M B ≤ −20.5 − z) the fraction of red (U − B ≥ 1) galaxies depends on δ at least up to z ∼ 1, with red galaxies residing mainly in high densities. This trend becomes weaker for increasing redshifts, and it is mirrored by the behaviour of the fraction of galaxies with D4000Å break ≥ 1.4. We also find that up to z ∼ 1 the fraction of galaxies with log(EW[OII]) ≥ 1.15 is higher for lower δ, and also this dependence weakens for increasing z. Given the triple dependence among galaxy colours, stellar mass and δ, the colour-δ relation that we find in the luminosity-selected sample can be due to the broad range of stellar masses embedded in the sample. Thus, we study the colour-δ relation in narrow mass bins within mass complete subsamples, defining red galaxies with a colour threshold roughly parallel to the red sequence in the colour-mass plane. We find that once mass is fixed the colour-δ relation is globally flat up to z ∼ 1 for galaxies with log(M/M ⊙) 10.7. This means that for these masses any colour-δ relation found within a luminosity-selected sample is the result of the combined colour-mass and mass-δ relations. On the contrary, even at fixed mass we observe that within 0.1 ≤ z ≤ 0.5 the fraction of red galaxies with log(M/M ⊙) 10.7 depends on δ. For these mass and redshift ranges, environment affects directly also galaxy colours. Conclusions. We suggest a scenario in which the colour depends primarily on stellar mass, but for an intermediate mass regime (10.2 log(M/M ⊙) 10.7) the local density modulates this dependence. These relatively low mass galaxies formed more recently, in an epoch when more evolved structures were already in place, and their longer SFH allowed environment-driven physical processes to operate during longer periods of time.
Astronomy & Astrophysics, 2008
We study the spatial clustering of 538 X-ray selected AGN in the 2 deg 2 XMM-COSMOS field that ar... more We study the spatial clustering of 538 X-ray selected AGN in the 2 deg 2 XMM-COSMOS field that are spectroscopically identified with I AB < 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 L 0.5−10 = 6.3 × 10 43 erg s −1 , respectively. A strong clustering signal is detected at ∼18σ level, which is the most significant measurement obtained to date for clustering of X-ray selected AGN. By fitting the projected correlation function w(r p) with a power law on scales of r p = 0.3−40 h −1 Mpc, we derive a best-fit comoving correlation length of r 0 = 8.6 ± 0.5 h −1 Mpc and slope of γ = 1.88 ± 0.07 (Poissonian errors; bootstrap errors are about a factor of 2 larger). An excess signal is observed in the range r p ∼ 5−15 h −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(r p) in a narrower range around the peak of the redshift distribution (e.g. z = 0.4−1.6), the correlation length decreases to r 0 ∼ 5−6 h −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 × 10 10 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 r 0 ∼ 8 h −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 × 10 12 M 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.
Astronomy & Astrophysics, 2010
We present the galaxy stellar mass function (GSMF) to redshift z 1, based on the analysis of abou... more 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 deg 2 , 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 galaxy bimodality 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 GSMF evolution at intermediateto-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 GBMF for the blue galaxy population at intermediate-high masses.
Astronomy & Astrophysics, 2008
We use one of the deepest spectroscopic samples of broad-line active galactic nuclei (AGN) curren... more We use one of the deepest spectroscopic samples of broad-line active galactic nuclei (AGN) currently available, extracted from the VIMOS VLT Deep Survey (VVDS), to compute the Mg ii and C iv virial-mass estimates of 120 super-massive black holes in the redshift range 1.0 < z < 1.9 and 2.6 < z < 4.3. We find that the mass-luminosity relation shows considerably enhanced dispersion towards low AGN luminosities (log L bol ∼ 45). At these luminosities, there is a substantial fraction of black holes accreting far below their Eddington limit (L bol /L Edd < 0.1), in marked contrast to what is generally found for AGN of higher luminosities. We speculate that these may be AGN on the decaying branch of their lightcurves, well past their peak activity. This would agree with recent theoretical predictions of AGN evolution. In the electronic Appendix of this paper we publish an update of the VVDS type-1 AGN sample, including the first and most of the second-epoch observations. This sample contains 298 objects of which 168 are new.
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Papers by Marco Scodeggio