The Cosmic Evolution Survey (COSMOS): The relationships between galaxy morphology, colors, mass and environment at z 3c 0.7

We present a detailed analysis of the evolution of the rest-frame B-band morphology of K-selected galaxies with 0 < z < 2.5. This work is based on the K20 spectroscopic sample (Ks < 20) located within the Chandra Deep Field South area, coupled with the public deep GOODS (Great Observatories Origins Deep Surveys) Hubble Space Telescope (HST)+Advanced Camera for Surveys (ACS) multiband optical imaging available in that field. Thanks to the spectroscopic completeness of this catalogue reaching 94 per cent, we can compare the morphological and spectroscopic properties of galaxies with unprecedented detail. Our morphological analysis includes visual inspection and automatic procedures using both parametric (e.g. the S\ue9rsic indices treated by the GALFIT and GASPHOT packages) and non-parametric (concentration, asymmetry and clumpiness, CAS) methods. By exploiting the four-band deep ACS imaging we account in detail for morphological K-correction as a function of the redshift and show that, while parametric methods do not efficiently separate early- and late-type galaxies, non-parametric ones prove more efficient and reliable. Our analysis classifies the K20 galaxies as: 60/300 (20 per cent, class 1) normal ellipticals/S0 14/300 (4 per cent, class 2) perturbed or peculiar ellipticals; 80/300 (27 per cent, class 3) normal spirals; 48/300 (16 per cent, class 4) perturbed or actively star-forming spirals; 98/300 (33 per cent, class 5) irregulars. The morphological and spectroscopic classifications are compatible with each other for more than 90 per cent of the sample galaxies, while seven class-1 E/S0 objects show emission lines and 11 spirals and irregulars (classes 3+4+5) have purely absorption-line spectra. The evolution of the merging fraction is constrained up to z~ 2, by carefully accounting the effects of morphological K-correction: both asymmetry criterion and pair statistics show an increasing merging fraction as a function of redshift. We finally analyse the redshift dependence of the effective radii for early- and late-type galaxies and find some mild evidence for a decrease with z of the early-type galaxy sizes, while the discs and irregulars remain constant. Altogether, this analysis of the K20 sample indicates the large predominance of spirals and irregulars at 0.5 < z < 1.5 in K-band selected samples at even moderate depths

Stellar and total baryon mass fractions in groups and clusters since Redshift 1

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 deg2 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 ~1013-1015 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 langMrang = 5 × 1013 M ☉ to langMrang = 7 × 1014 M ☉. After consideration of a plausible contribution due to intracluster 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 langMrang = 5 × 1013 M ☉. The discrepancy decreases toward higher total masses, such that it is 1σ at langMrang = 7 × 1014 M ☉. We discuss this result in terms of nongravitational processes such as feedback and filamentary heating