We explore the simple inter-relationships between mass, star formation rate, and environment in the SDSS, zCOSMOS, and other deep surveys. We take a purely empirical approach in identifying those features of galaxy evolution that are demanded by the data and then explore the analytic consequences of these. We show that the differential effects of mass and environment are completely separable to z ~ 1, leading to the idea of two distinct processes of "mass quenching" and "environment quenching." The effect of environment quenching, at fixed over-density, evidently does not change with epoch to z ~ 1 in zCOSMOS, suggesting that the environment quenching occurs as large-scale structure develops in the universe, probably through the cessation of star formation in 30%-70% of satellite galaxies. In contrast, mass quenching appears to be a more dynamic process, governed by a quenching rate. We show that the observed constancy of the Schechter M* and α s for star-forming galaxies demands that the quenching of galaxies around and above M* must follow a rate that is statistically proportional to their star formation rates (or closely mimic such a dependence). We then postulate that this simple mass-quenching law in fact holds over a much broader range of stellar mass (2 dex) and cosmic time. We show that the combination of these two quenching processes, plus some additional quenching due to merging naturally produces (1) a quasi-static single Schechter mass function for star-forming galaxies with an exponential cutoff at a value M* that is set uniquely by the constant of proportionality between the star formation and mass quenching rates and (2) a double Schechter function for passive galaxies with two components. The dominant component (at high masses) is produced by mass quenching and has exactly the same M* as the star-forming galaxies but a faint end slope that differs by Δα s ~ 1. The other component is produced by environment effects and has the same M* and α s as the star-forming galaxies but an amplitude that is strongly dependent on environment. Subsequent merging of quenched galaxies will modify these predictions somewhat in the denser environments, mildly increasing M* and making α s slightly more negative. All of these detailed quantitative inter-relationships between the Schechter parameters of the star-forming and passive galaxies, across a broad range of environments, are indeed seen to high accuracy in the SDSS, lending strong support to our simple empirically based model. We find that the amount of post-quenching "dry merging" that could have occurred is quite constrained. Our model gives a prediction for the mass function of the population of transitory objects that are in the process of being quenched. Our simple empirical laws for the cessation of star formation in galaxies also naturally produce the "anti-hierarchical" run of mean age with mass for passive galaxies, as well as the qualitative variation of formation timescale indicated by the relative α-element abundances.

Examining a sample of massive galaxies at 1:4 < z < 2:5 with K Vega < 22 from GOODS, we compare photometry from Spitzer at mid-and far-IR to submillimeter, radio, and rest-frame UV wavelengths, to test the agreement between different tracers of star formation rates (SFRs) and to explore the implications for galaxy assembly. For z $ 2 galaxies with moderate luminosities (L 8 m < 10 11 L ), we find that the SFR can be estimated consistently from the multiwavelength data based on local luminosity correlations. However, 20%Y30% of massive galaxies, and nearly all those with L 8 m > 10 11 L , show a mid-IR excess that is likely due to the presence of obscured active nuclei, as shown in a companion paper. There is a tight and roughly linear correlation between stellar mass and SFR for 24 mYdetected galaxies. For a given mass, the SFR at z ¼ 2 was larger by a factor of $4 and $30 relative to that in star-forming galaxies at z ¼ 1 and 0, respectively. Typical ultraluminous infrared galaxies (ULIRGs) at z ¼ 2 are relatively ''transparent'' to ultraviolet light, and their activity is long lived (k400 Myr), unlike that in local ULIRGs and high-redshift submillimeter-selected galaxies. ULIRGs are the common mode of star formation in massive galaxies at z ¼ 2, and the high duty cycle suggests that major mergers are not the dominant trigger for this activity. Current galaxy formation models underpredict the normalization of the mass-SFR correlation by about a factor of 4 and the space density of ULIRGs by an order of magnitude but give better agreement for z > 1:4 quiescent galaxies.

We present accurate photometric redshifts in the 2-deg 2 COSMOS field. The redshifts are computed with 30 broad, intermediate, and narrow bands covering the UV (GALEX), Visible-NIR (Subaru, CFHT, UKIRT and NOAO) and mid-IR (Spitzer/IRAC). A χ 2 template-fitting method (Le Phare) was used and calibrated with large spectroscopic samples from VLT-VIMOS and Keck-DEIMOS. We develop and implement a new method which accounts for the contributions from emission lines ([O II], Hβ, Hα and Lyα) to the spectral energy distributions (SEDs). The treatment of emission lines improves the photo-z accuracy by a factor of 2.5. Comparison of the derived photo-z with 4148 spectroscopic redshifts (i.e. ∆z = z s − z p ) indicates a dispersion of σ ∆z/(1+zs) = 0.007 at i + AB < 22.5, a factor of 2 − 6 times more accurate than earlier photo-z in the COSMOS, CFHTLS and COMBO-17 survey fields. At fainter magnitudes i + AB < 24 and z < 1.25, the accuracy is σ ∆z/(1+zs) = 0.012. The deep NIR and IRAC coverage enables the photo-z to be extended to z ∼ 2 albeit with a lower accuracy (σ ∆z/(1+zs) = 0.06 at i + AB ∼ 24). The redshift distribution of large magnitude-selected samples is derived and the median redshift is found to range from z m = 0.66 at 22 < i + AB < 22.5 to z m = 1.06 at 24.5 < i + AB < 25. At i + AB < 26.0, the multi-wavelength COSMOS catalog includes approximately 607,617 objects. The COSMOS-30 photo-z enable the full exploitation of this survey for studies of galaxy and large scale structure evolution at high redshift.

A simple two-color selection based on B-, z-, and K-band photometry is proposed for culling galaxies at 1:4 P z P 2:5 in K-selected samples and classifying them as star-forming or passive systems. The method is calibrated on the highly complete spectroscopic redshift database of the K20 survey, verified with simulations and tested on other data sets. Requiring BzK ¼ (z À K ) AB À (B À z) AB > À0:2 allows us to select actively starforming galaxies at z k1:4, independently of their dust reddening. On the other hand, objects with BzK < À0:2 and (z À K ) AB > 2:5 colors include passively evolving galaxies at z k1:4, often with spheroidal morphologies. Simple recipes to estimate the reddening, star formation rates (SFRs), and masses of BzK-selected galaxies are derived and are calibrated on K < 20 galaxies. These K < 20 galaxies have typical stellar masses of $10 11 M and sky and volume densities of $1 arcmin À2 and $10 À4 Mpc À3 , respectively. Based on their UV (reddeningcorrected ), X-ray, and radio luminosities, the BzK-selected star-forming galaxies with K < 20 turn out to have average SFR % 200 M yr À1 and median reddening E(B À V ) $ 0:4. This SFR is a factor of 10 higher than that of z $1 dusty extremely red objects, and a factor of 3 higher than found for z $ 2 UV-selected galaxies, both at similar K limits. Besides missing the passively evolving galaxies, the UV selection appears to miss some relevant fraction of the z $ 2 star-forming galaxies with K < 20, and hence of the (obscured) SFR density at this redshift. The high SFRs and masses add to other existing evidence that these z ¼ 2 star-forming galaxies may be among the precursors of z ¼ 0 early-type galaxies. A V/V max test suggests that such a population may be increasing in number density with increasing redshift. Theoretical models cannot reproduce simultaneously the space density of both passively evolving and highly star-forming galaxies at z ¼ 2. In view of Spitzer Space Telescope observations, an analogous technique based on RJL photometry is proposed to complement the BzK selection and to identify massive galaxies at 2:5 P z P 4:0. By selecting passively evolving galaxies as well as actively star-forming galaxies (including strongly dust-reddened ones), these color criteria should help in completing the census of the stellar mass and of the SFR density at high redshift.

We have determined the cosmological evolution of the density of active galactic nuclei (AGN) and of their N H distribution as a function of the un-absorbed 2-10 keV luminosity up to redshift 4. We used the HELLAS2XMM sample combined with other published catalogs, yielding a total of 508 AGN. Our best fit is obtained with a luminosity-dependent density evolution (LDDE) model where low luminosity (L X ∼10 43 erg s −1 ) AGN peak at z∼0.7, while high luminosity AGN (L X >10 45 erg s −1 ) peak at z∼2.0. A pure luminosity evolution model (PLE) can instead be rejected.There is evidence that the fraction of absorbed (N H >10 22 cm −2 ) AGN decreases with the intrinsic X-ray luminosity, and increases with the redshift.Our best fit solution provides a good fit to the observed counts, the cosmic X-ray background, and to the observed fraction of absorbed AGN as a function of the flux in the 10 −15 10 44 erg s −1 ) AGN have a density of 267 deg −2 at fluxes S 2−10 >10 −15 erg cm −2 s −1 . Using these results, we estimate a density of supermassive black holes in the local Universe of ρ BH = 3.2 h 2 70 × 10 5 M ⊙ Mpc −3 , which is consistent with the recent measurements of the black hole mass function in the local galaxies.

Aims. The aim of this work is to investigate the physical, structural and evolutionary properties of old, passive galaxies at z > 1.4 and to place new constraints on massive galaxy formation and evolution. Methods. We combine ultradeep optical spectroscopy from the GMASS project (Galaxy Mass Assembly ultradeep Spectroscopic Survey) with GOODS multi-band (optical to mid-infrared) photometry and HST imaging to study a sample of spectroscopically identified passive galaxies at 1.39 < z < 1.99 selected from Spitzer Space Selescope imaging at 4.5 µm. Results. A stacked spectrum with an equivalent integration time of ∼500 h was obtained and compared with libraries of synthetic stellar population spectra. The stacked spectrum is publicly released. The spectral and photometric SED properties indicate very weak or absent star formation, moderately old stellar ages of ≈1 Gyr (for solar metallicity) and stellar masses in the range of 10 10−11 M , thus implying that the major star formation and assembly processes for these galaxies occurred at z > 2. No X-ray emission was found neither from individual galaxies nor from a stacking analysis of the sample. Only one galaxy shows a marginal detection at 24 µm. These galaxies have morphologies that are predominantly compact and spheroidal. However, their sizes (R e 1 kpc) are much smaller than those of spheroids in the present-day Universe. Their stellar mass surface densities are consequently higher by ≈1 dex if compared to spheroids at z ≈ 0 with the same mass. Their rest-frame B-band surface brightness scales with the effective radius, but the offset with respect to the surface brightness of the local Kormendy relation is too large to be explained by simple passive evolution. At z ≈ 1, a larger fraction of passive galaxies follows the z ≈ 0 size-mass relation. Superdense relics with R e ≈ 1 kpc are extremely rare at z ≈ 0 with respect to z > 1, and absent if R e < 1 kpc. Because of the similar sizes and mass densities, we suggest that the superdense passive galaxies at 1 < z < 2 are the remnants of the powerful starbursts occurring in submillimeter-selected galaxies at z > 2. The results are compared with theoretical models and the main implications discussed in the framework of massive galaxy formation and evolution.

Over the past two decades observations and theoretical simulations have established a global frame-work of galaxy formation and evolution in the young Universe (1-3).Galaxies formed as baryonic gas cooled at the centres of collapsing dark matter halos. Mergers of halos and galaxies led to the hierarchical build-up of galaxy mass.It remains unclear, however, over what timescales galaxies were assembled and when and how bulges and disks, the primary components of present day galaxies, were formed. It is also puzzling that the most massive galaxies were more abundant and were forming stars more rapidly at early epochs than expected from models (4-7). A major step forward in understanding these issues requires well resolved physical information on individual galaxies at high redshift. Here we report adaptive optics, spectroscopic observations of a representative luminous star forming galaxy when the Universe was only twenty percent of its current age. The far superior angular resolution of these data compared to our first study (8) reveals the physical and dynamical properties of a high redshift galaxy in unprecedented detail. A large and massive rotating proto-disk is channelling gas toward a growing central stellar bulge hosting an accreting massive black hole. The high gas surface densities, large star formation rate and moderately young stellar ages suggest rapid assembly, fragmentation and conversion to stars of an initially very gas rich protodisk, with no obvious evidence for a major merger. 2Imaging spectroscopy of high redshift galaxies at high angular resolution of well understood rest-frame optical spectral diagnostics is now becoming feasible with advanced instruments on large ground-based telescopes. This promises new empirical information about the crucial epoch of galaxy evolution near cosmological redshift z~2, about 3 billion years after the Big Bang when the Universe was about 20% of its current age. We have recently begun a study of a representative sample of z~2-3 star forming galaxies, selected based on their rest-frame ultra-violet/optical fluxes and colours, with the near-infrared integral field spectrometer SINFONI on the Very Large Telescope of the European Southern Observatory (9, 10). Our first results (8) revealed that fairly large and massive proto-disk galaxies were present already at z~2-3. We did not have sufficient resolution, however, to distinguish unambiguously between a merger and disk interpretation, or to resolve the bulge and disk components. For one of these luminous star forming galaxies, BzK-15504 (z=2.38: 11, 12), the presence of a nearby star and excellent atmospheric conditions now allowed us, for the first time, to take full advantage of the adaptive optics mode of SINFONI. We achieved an angular resolution of ~0.15" (1.2 kpc or 4000 light years), more than three times better than in our previous work.BzK-15504 is a fairly typical representative of rest-frame optically bright, actively star forming galaxies at that redshift (for details see caption of Fig.1 and Suppleme...

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.