The evolution of galaxy clustering from z=0 to z~=4.5 is analysed using the angular correlation function and the photometric redshift distribution of galaxies brighter than IAB<=28.5 in the Hubble Deep Field North. The reliability of the photometric redshift estimates is discussed on the basis of the available spectroscopic redshifts, comparing different codes and investigating the effects of photometric errors. The redshift bins in which the clustering properties are measured are then optimized to take into account the uncertainties of the photometric redshifts. The results show that the comoving correlation length r0 has a small decrease in the range 0<~z<~1 followed by an increase at higher z. We compare these results with the theoretical predictions of a variety of cosmological models belonging to the general class of Cold Dark Matter scenarios, including Einstein-de Sitter models, an open model and a flat model with non-zero cosmological constant. Comparison with the expected mass clustering evolution indicates that the observed high-redshift galaxies are biased tracers of the dark matter with an effective bias b strongly increasing with redshift. Assuming an Einstein-de Sitter universe, we obtain b~=2.5 at z~=2 and b~=5 at z~=4. These results support theoretical scenarios of biased galaxy formation in which the galaxies observed at high redshift are preferentially located in more massive haloes. Moreover, they suggest that the usual parameterization of the clustering evolution as ξ(r,z)=ξ(r,0)(1+z)-(3+ɛ) is not a good description for any value of ɛ. Comparison of the clustering amplitudes that we measured at z~=3 with those reported by Adelberger et al. and Giavalisco et al., based on a different selection, suggests that the clustering depends on the abundance of the objects: more abundant objects are less clustered, as expected in the paradigm of hierarchical galaxy formation. The strong clustering and high bias measured at z~=3 are consistent with the expected density of massive haloes predicted in the frame of the various cosmologies considered here. At z~=4, the strong clustering observed in the Hubble Deep Field requires a significant fraction of massive haloes to be already formed by that epoch. This feature could be a discriminant test for the cosmological parameters if confirmed by future observations

This Special Issue of the Astrophysical Journal Letters is dedicated to presenting initial results from the Great Observatories Origins Deep Survey (GOODS) that are primarily, but not exclusively, based on multi-band imaging data obtained with the Hubble Space Telescope (HST) and the Advanced Camera for Surveys (ACS). The survey covers roughly 320 square arcminutes in the ACS F435W, F606W, F814W, and F850LP bands, divided into two well-studied fields. Existing deep observations from the Chandra X-ray Observatory (CXO) and groundbased facilities are supplemented with new, deep imaging in the optical and

The Sloan Digital Sky Survey III (SDSS-III) presents the first spectroscopic data from the Baryon Oscillation Spectroscopic Survey (BOSS). This ninth data release (DR9) of the SDSS project includes 535,995 new galaxy spectra (median z ∼ 0.52), 102,100 new quasar spectra (median z ∼ 2.32), and 90,897 new stellar spectra, along with the data presented in previous data releases. These spectra were obtained with the new BOSS spectrograph and were taken between 2009 December and 2011 July. In addition, the stellar parameters pipeline, which determines radial velocities, surface temperatures, surface gravities, and metallicities of stars, has been updated and refined with improvements in temperature estimates for stars with T eff < 5000 K and in metallicity estimates for stars with [Fe/H] > −0.5. DR9 includes new stellar parameters for all stars presented in DR8, including stars from SDSS-I and II, as well as those observed as part of the SDSS-III Sloan Extension for Galactic Understanding and Exploration-2 (SEGUE-2).

Context. Establishing the number of faint active galactic nuclei (AGNs) at z = 4−6 is crucial to understanding their cosmological importance as main contributors to the reionization of the Universe. Aims. In order to derive the AGN contribution to the cosmological ionizing emissivity we have selected faint AGN candidates at z > 4 in the CANDELS GOODS-South field, which is one of the deepest fields with extensive multiwavelength coverage from Chandra, HST, Spitzer, and various ground-based telescopes. Methods. We have adopted a relatively novel criterion. As a first step, high redshift galaxies are selected in the NIR H band down to very faint levels (H ≤ 27) using reliable photometric redshifts. At z > 4 this corresponds to a selection criterion based on the galaxy rest-frame UV flux. AGN candidates are then picked up from this parent sample if they show X-ray fluxes above a threshold of F X ∼ 1.5 × 10 −17 erg cm −2 s −1 (0.5−2 keV), corresponding to a probability of spurious detections of 2 × 10 −4 in the deep X-ray 4 Ms Chandra image. Results. We have found 22 AGN candidates at z > 4 and we have derived the first estimate of the UV luminosity function in the redshift interval 4 < z < 6.5 and absolute magnitude interval −22.5 M 1450 −18.5 typical of local Seyfert galaxies. The faint end of the derived luminosity function is about two to four magnitudes fainter at z ∼ 4−6 than that derived from previous UV surveys. We estimated ionizing emissivities and hydrogen photoionization rates in the same redshift interval under reasonable assumptions and after discussion of possible caveats, the most important being the large uncertainties involved in the estimate of photometric redshift for sources with featureless, almost power-law SEDs and/or low average escape fraction of ionizing photons from the AGN host galaxies. Both effects could, in principle, significantly reduce the estimated average volume densities and/or ionizing emissivities, especially at the highest redshifts. Conclusions. At z = 4−6.5 we argue that, under reasonable evaluations of possible biases, the probed AGN population can produce photoionization rates consistent with that required to keep the intergalactic medium observed in the Lyman-α forest of high redshift QSO spectra highly ionized, providing an important contribution to the cosmic reionization.

Aims. The goal of this work is to measure the evolution of the Galaxy Stellar Mass Function and of the resulting Stellar Mass Density up to redshift 4, in order to study the assembly of massive galaxies in the high redshift Universe. Methods. We have used the GOODS-MUSIC catalog, containing ∼3000 Ks-selected galaxies with multi-wavelength coverage extending from the U band to the Spitzer 8 µm band, of which 27% have spectroscopic redshifts and the remaining fraction have accurate photometric redshifts. On this sample we have applied a standard fitting procedure to measure stellar masses. We compute the Galaxy Stellar Mass Function and the resulting Stellar Mass Density up to redshift 4, taking into proper account the biases and incompleteness effects. Results. Within the well known trend of global decline of the Stellar Mass Density with redshift, we show that the decline of the more massive galaxies may be described by an exponential timescale of 6 Gyr up to z 1.5, and proceeds much faster thereafter, with an exponential timescale of 0.6 Gyr. We also show that there is some evidence for a differential evolution of the Galaxy Stellar Mass Function, with low mass galaxies evolving faster than more massive ones up to z 1−1.5 and that the Galaxy Stellar Mass Function remains remarkably flat (i.e. with a slope close to the local one) up to z 1−1.3. Conclusions. The observed behaviour of the Galaxy Stellar Mass Function is consistent with a scenario where about 50% of presentday massive galaxies formed at a vigorous rate in the epoch between redshift 4 and 1.5, followed by a milder evolution until the present-day epoch.

Abstract. We present a detailed analysis of the stellar mass content of galaxies up to z = 2.5 as obtained from the K20 spectrophotometric galaxy sample. We have applied and compared two different methods to estimate the stellar mass M * from broad-band photometry: a Maximal Age approach, where we maximize the age of the stellar population to obtain the maximal mass compatible with the observed R − K color, and a Best Fit model, where the best-fitting spectrum to the complete UBVRIzJK s multicolor distribution is used. We find that the M * /L ratio decreases with redshift: in particular, the average M * /L ratio of early type galaxies decreases with z, with a scatter that is indicative of a range of star-formation time-scales and redshift of formation. More important, the typical M * /L ratio of massive early type galaxies is larger than that of less massive ones, suggesting that their stellar population formed at higher z. We show that the final K20 galaxy sample spans a range of stellar masses from M * = 10 9 M to M * = 10 12 M : massive galaxies (M * ≥ 10 11 M ) are common at 0.5 < z < 1, and are detected also up to z 2. We compute the Galaxy Stellar Mass Function at various z, of which we observe only a mild evolution (i.e. by 20-30%) up to z 1. At z > 1, the evolution in the normalization of the GSMF appears to be much faster: at z 2, about 35% of the present day stellar mass in objects with M * 10 11 M appear to have assembled. We also detect a change in the physical nature of the most massive galaxies: at z < ∼ 0.7, all galaxies with M > 10 11 M are early type, while at higher z a population of massive star-forming galaxies progressively appears. We finally analyze our results in the framework of Λ-CDM hierarchical models. First, we show that the large number of massive galaxies detected at high z does not violate any fundamental Λ-CDM constraint based on the number of massive DM halos. Then, we compare our results with the predictions of several renditions of both semianalytic as well as hydro-dynamical models. The predictions from these models range from severe underestimates to slight overestimates of the observed mass density at ≤2. We discuss how the differences among these models are due to the different implementation of the main physical processes.

Aims. We present a high quality multiwavelength (from 0.3 to 8.0 µm) catalog of the large and deep area in the GOODS Southern Field covered by the deep near-IR observations obtained with the ESO VLT. Methods. The catalog is entirely based on public data: in our analysis, we have included the F435W, F606W, F775W and F850LP ACS images, the JHKs VLT data, the Spitzer data provided by IRAC instrument (3.6, 4.5, 5.8 and 8.0 µm), and publicly available U-band data from the 2.2ESO and VLT-VIMOS. We describe in detail the procedures adopted to obtain this multiwavelength catalog. In particular, we developed a specific software for the accurate "PSF-matching" of space and ground-based images of different resolution and depth (ConvPhot), of which we analyse performances and limitations. We have included both z-selected, as well as Ks-selected objects, yielding a unique, self-consistent catalog. The largest fraction of the sample is 90% complete at z 26 or Ks 23.8 (AB scale). Finally, we cross-correlated our data with all the spectroscopic catalogs available to date, assigning a spectroscopic redshift to more than 1000 sources. Results. The final catalog is made up of 14 847 objects, at least 72 of which are known stars, 68 are AGNs, and 928 galaxies with spectroscopic redshift (668 galaxies with reliable redshift determination). We applied our photometric redshift code to this data set, and the comparison with the spectroscopic sample shows that the quality of the resulting photometric redshifts is excellent, with an average scatter of only 0.06. The full catalog, which we named GOODS-MUSIC (MUltiwavelength Southern Infrared Catalog), including the spectroscopic information, is made publicly available, together with the software specifically designed to this end.

The Sloan Digital Sky Survey (SDSS) has been in operation since 2000 April. This paper presents the tenth public data release (DR10) from its current incarnation, SDSS-III. This data release includes the first spectroscopic data from the Apache Point Observatory Galaxy Evolution Experiment (APOGEE), along with spectroscopic data from the Baryon Oscillation Spectroscopic Survey (BOSS) taken through 2012 July. The APOGEE instrument is a near-infrared R ∼ 22,500 300-fiber spectrograph covering 1.514-1.696 µm. The APOGEE survey is studying the chemical abundances and radial velocities of roughly 100,000 red giant star candidates in the bulge, bar, disk, and halo of the Milky Way. DR10 includes 178,397 spectra of 57,454 stars, each typically observed three or more times, from APOGEE. Derived quantities from these spectra (radial velocities, effective temperatures, surface gravities, and metallicities) are also included. arXiv:1307.7735v3 [astro-ph.IM] 17 Jan 2014 2 DR10 also roughly doubles the number of BOSS spectra over those included in the ninth data release. DR10 includes a total of 1,507,954 BOSS spectra, comprising 927,844 galaxy spectra; 182,009 quasar spectra; and 159,327 stellar spectra, selected over 6373.2 deg 2 .