We present the COSMOS2015 a catalog which contains precise photometric redshifts and stellar masses for more than half a million objects over the 2deg 2 COSMOS field. Including new Y JHK s images from the UltraVISTA-DR2 survey, Y -band from Subaru/Hyper-Suprime-Cam and infrared data from the Spitzer Large Area Survey with the Hyper-Suprime-Cam Spitzer legacy program, this near-infraredselected catalog is highly optimized for the study of galaxy evolution and environments in the early Universe. To maximise catalog completeness for bluer objects and at higher redshifts, objects have been detected on a χ 2 sum of the Y JHK s and z ++ images. The catalog contains ∼ 6 × 10 5 objects in the 1.5 deg 2 UltraVISTA-DR2 region, and ∼ 1.5 × 10 5 objects are detected in the "ultra-deep stripes" (0.62 deg 2 ) at K s ≤ 24.7 (3σ, 3 , AB magnitude). Through a comparison with the zCOSMOSbright spectroscopic redshifts, we measure a photometric redshift precision of σ ∆z/(1+zs) = 0.007 and a catastrophic failure fraction of η = 0.5%. At 3 < z < 6, using the unique database of spectroscopic redshifts in COSMOS, we find σ ∆z/(1+zs) = 0.021 and η = 13.2%. The deepest regions reach a 90% completeness limit of 10 10 M to z = 4. Detailed comparisons of the color distributions, number counts, and clustering show excellent agreement with the literature in the same mass ranges. COSMOS2015 represents a unique, publicly available, valuable resource with which to investigate the evolution of galaxies within their environment back to the earliest stages of the history of the Universe. The COSMOS2015 catalog is distributed via anonymous ftp b and through the usual astronomical archive systems (CDS, ESO, IRSA).

The rest-frame ultraviolet properties of galaxies during the first three billion years of cosmic time (redshift z > 4) indicate a rapid evolution in the dust obscuration of such galaxies. This evolution implies a change in the average properties of the interstellar medium, but the measurements are systematically uncertain owing to untested assumptions and the inability to detect heavily obscured regions of the galaxies. Previous attempts to measure the interstellar medium directly in normal galaxies at these redshifts have failed for a number of reasons, with two notable exceptions. Here we report measurements of the forbidden C ii emission (that is, [C II]) from gas, and the far-infrared emission from dust, in nine typical star-forming galaxies about one billion years after the Big Bang (z ≈ 5-6). We find that these galaxies have thermal emission that is less than 1/12 that of similar systems about two billion years later, and enhanced [C II] emission relative to the far-infrared continuum, confirming a strong evolution in the properties of the interstellar medium in the early Universe. The gas is distributed over scales of one to eight kiloparsecs, and shows diverse dynamics within the sample. These results are consistent with early galaxies having significantly less dust than typical galaxies seen at z < 3 and being comparable in dust content to local low-metallicity systems.

We explore the redshift evolution of the specific star formation rate (SSFR) for galaxies of different stellar mass by drawing on a deep 3.6 µm-selected sample of > 10 5 galaxies in the 2 deg 2 COSMOS field. The average star formation rate (SFR) for sub-sets of these galaxies is estimated with stacked 1.4 GHz radio continuum emission. We separately consider the total sample and a subset of galaxies that shows evidence for substantive recent star formation in the rest-frame optical spectral energy distributions. At redshifts 0.2 < z < 3 both populations show a strong and mass-independent decrease in their SSFR towards the present epoch. It is best described by a power-law (1 + z) n , where n ∼ 4.3 for all galaxies and n ∼ 3.5 for star forming (SF) sources. The decrease appears to have started at z > 2, at least for high-mass (M * 4 × 10 10 M ⊙ ) systems where our conclusions are most robust. Our data show that there is a tight correlation with power-law dependence, SSFR ∝ M * β , between SSFR and stellar mass at all epochs. The relation tends to flatten below M * ≈ 10 10 M ⊙ if quiescent galaxies are included; if they are excluded from the analysis a shallow index β SFG ≈ −0.4 fits the correlation. On average, higher mass objects always have lower SSFRs, also among SF galaxies. At z > 1.5 there is tentative evidence for an upper threshold in SSFR that an average galaxy cannot exceed, possibly due to gravitationally limited molecular gas accretion. It is suggested by a flattening of the SSFR-M * relation (also for SF sources), but affects massive (> 10 10 M ⊙ ) galaxies only at the highest redshifts. Since z = 1.5 there thus is no direct evidence that galaxies of higher mass experience a more rapid waning of their SSFR than lower mass SF systems. In this sense, the data rule out any strong 'downsizing' in the SSFR. We combine our results with recent measurements of the galaxy (stellar) mass function in order to determine the characteristic mass of a SF galaxy: we find that since z ∼ 3 the majority of all new stars were always formed in galaxies of M * = 10 10.6±0.4 M ⊙ . In this sense, too, there is no 'downsizing'. Finally, our analysis constitutes the most extensive SFR density determination with a single technique out to z = 3. Recent Herschel results are consistent with our results, but rely on far smaller samples.Note. -Median stacking-based average 1.4 GHz radio flux densities and derived average quantities for all our bins in mass and redshift for star forming systems within our mass-selected sample. For details see caption of Tab. 2. † Mass bin contains data below the limit of mass representativeness and yields an upper limit to the average SFR (see Sec. 2.6 for further details.) ⋆ First mass bin above the limit of representativeness (see Sec. 2.6) which contains a low fraction (< 15 %) of optically faint objects with m AB (i + ) ≥ 25.5 for which the photo-z accuracy is degraded (see Sec. 2.2 for further details). The average SFR measured in this bin might be slightly overestimated towards higher values (se...

We aim to measure the average dust and molecular gas content of massive star-forming galaxies (>3 × 10 10 M ) up to z = 4 in the COSMOS field to determine if the intense star formation observed at high redshift is induced by major mergers or is caused by large gas reservoirs. Firstly, we measured the evolution of the average spectral energy distributions as a function of redshift using a stacking analysis of Spitzer, Herschel, LABOCA, and AzTEC data for two samples of galaxies: normal star-forming objects and strong starbursts, as defined by their distance to the main sequence. We found that the mean intensity of the radiation field U heating the dust (strongly correlated with dust temperature) increases with increasing redshift up to z = 4 in main-sequence galaxies. We can reproduce this evolution with simple models that account for the decrease in the gas metallicity with redshift. No evolution of U with redshift is found in strong starbursts. We then deduced the evolution of the molecular gas fraction (defined here as M mol /(M mol + M )) with redshift and found a similar, steeply increasing trend for both samples. At z ∼ 4, this fraction reaches ∼60%. The average position of the main-sequence galaxies is on the locus of the local, normal star-forming disks in the integrated Schmidt-Kennicutt diagram (star formation rate versus mass of molecular gas), suggesting that the bulk of the star formation up to z = 4 is dominated by secular processes.

We present first results of a study aimed to constrain the star formation rate and dust content of galaxies at z≈2. We use a sample of BzK-selected star-forming galaxies, drawn from the COSMOS survey, to perform a stacking analysis of their 1.4 GHz radio continuum as a function of different stellar population properties, after removing AGN contaminants from the sample. Dust unbiased star formation rates are derived from radio fluxes assuming the local radio-IR correlation. The main results of this work are: i) specific star formation rates are constant over about 1 dex in stellar mass and up to the highest stellar mass probed; ii) the dust attenuation is a strong function of galaxy stellar mass with more massive galaxies being more obscured than lower mass objects; iii) a single value of the UV extinction applied to all galaxies would lead to grossly underestimate the SFR in massive galaxies; iv) correcting the observed UV luminosities for dust attenuation based on the Calzetti recipe provide results in very good agreement with the radio derived ones; v) the mean specific star formation rate of our sample steadily decreases by a factor of ∼ 4 with decreasing redshift from z = 2.3 to 1.4 and a factor of ∼ 40 down the local Universe.These empirical SFRs would cause galaxies to dramatically overgrow in mass if maintained all the way to low redshifts, we suggest that this does not happen because star formation is progressively quenched, likely starting from the most massive galaxies.

The Sloan Digital Sky Survey has validated and made publicly available its Second Data Release. This data release consists of 3324 square degrees of five-band (u g r i z) imaging data with photometry for over 88 million unique objects, 367,360 spectra of galaxies, quasars, stars and calibrating blank sky patches selected over 2627 degrees of this area, and tables of measured parameters from these data. The imaging data reach a depth of r ~ 22.2 (95% completeness limit for point sources) and are photometrically and astrometrically calibrated to 2% rms and 100 milli-arcsec rms per coordinate, respectively. The imaging data have all been processed through a new version of the SDSS imaging pipeline, in which the most important improvement since the last data release is fixing an error in the model fits to each object. The result is that model magnitudes are now a good proxy for point spread function (PSF) magnitudes for point sources, and Petrosian magnitudes for extended sources. The spectroscopy extends from 3800 A to 9200 A at a resolution of 2000. The spectroscopic software now repairs a systematic error in the radial velocities of certain types of stars, and has substantially improved spectrophotometry. All data included in the SDSS Early Data Release and First Data Release are reprocessed with the improved pipelines, and included in the Second Data Release. The data are publically available as of 2004 March 15 via the web sites http://www.sdss.org/dr2 and http://skyserver.sdss.org .Comment: 24 pages, submitted to AJ. See ftp://ftp.astro.princeton.edu/strauss/sdss/dr2.ps for high-resolution figure

In the context of the VLA-COSMOS Deep project, additional VLA A array observations at 1.4 GHz were obtained for the central degree of the COSMOS field and combined with the existing data from the VLA-COSMOS Large project. A newly constructed Deep mosaic with a resolution of 2. 5 was used to search for sources down to 4σ with 1σ ≈ 12 μJy beam −1 in the central 50 × 50 . This new catalog is combined with the catalog from the Large project (obtained at 1. 5 × 1. 4 resolution) to construct a new Joint catalog. All sources listed in the new Joint catalog have peak flux densities of 5σ at 1. 5 and/or 2. 5 resolution to account for the fact that a significant fraction of sources at these low flux levels are expected to be slightly resolved at 1. 5 resolution. All properties listed in the Joint catalog, such as peak flux density, integrated flux density, and source size, are determined in the 2. 5 resolution Deep image. In addition, the Joint catalog contains 43 newly identified multi-component sources.

We investigate if the discrepancy between estimates of the total baryon mass fraction obtained from observations of the cosmic microwave background (CMB) and of galaxy groups/clusters persists when a large sample of groups is considered. To this purpose, 91 candidate X-ray groups/poor clusters at redshift 0.1 ≤ z ≤ 1 are selected from the COSMOS 2 deg 2 survey, based only on their X-ray luminosity and extent. This sample is complemented by 27 nearby clusters with a robust, analogous determination of the total and stellar mass inside R 500 . The total sample of 118 groups and clusters with z ≤ 1 spans a range in M 500 of ∼ 10 13 -10 15 M ⊙ . We find that the stellar mass fraction associated with galaxies at R 500 decreases with increasing total mass as M −0.37±0.04 500, independent of redshift. Estimating the total gas mass fraction from a recently derived, high quality scaling relation, the total baryon mass fraction (f stars+gas 500 = f stars 500 + f gas 500 ) is found to increase by ∼ 25% when M 500 increases from M = 5 × 10 13 M ⊙ to M = 7 × 10 14 M ⊙ . After consideration of a plausible contribution due to intra-cluster light (11-22% of the total stellar mass), and gas depletion through the hierarchical assembly process (10% of the gas mass), the estimated values of the total baryon mass fraction are still lower than the latest CMB measure of the same quantity (WMAP5), at a significance level of 3.3σ for groups of M = 5 × 10 13 M ⊙ . The discrepancy decreases towards higher total masses, such that it is 1σ at M = 7 × 10 14 M ⊙ . We discuss this result in terms of non-gravitational processes such as feedback and filamentary heating.