1305.1308 (M. Moresco et al.)

Spot the difference. Impact of different selection criteria on early-type galaxies observed properties in zCOSMOS 20-k sample    [PDF]

M. Moresco, L. Pozzetti, A. Cimatti, G. Zamorani, M. Bolzonella, F. Lamareille, M. Mignoli, E. Zucca, S. J. Lilly, C. M. Carollo, T. Contini, J. -P. Kneib, O. Le Fevre, V. Mainieri, A. Renzini, M. Scodeggio, S. Bardelli, A. Bongiorno, K. Caputi, O. Cucciati, S. de la Torre, L. de Ravel, P. Franzetti, B. Garilli, A. Iovino, P. Kampczyk, C. Knobel, K. Kovac, J. -F. Le Borgne, V. Le Brun, C. Maier, R. Pello', Y. Peng, E. Perez-Montero, V. Presotto, J. D. Silverman, M. Tanaka, L. Tasca, L. Tresse, D. Vergani, L. Barnes, R. Bordoloi, A. Cappi, C. Diener, A. M. Koekemoer, E. Le Floch, C. Lopez-Sanjuan, H. J. McCracken, P. Nair, P. Oesch, C. Scarlata, N. Scoville, N. Welikala

We present the analysis of photometric, spectroscopic and morphological properties for differently selected samples of early-type galaxies up to z=1 extracted from the zCOSMOS-20k spectroscopic survey. This analysis intends to explore the dependence of galaxy properties on the selection criterion adopted, to study the degree of contamination due to blue/star-forming/non-passive outliers, and to provide a comparison between different commonly used selection criteria. We extracted from the zCOSMOS-20k catalog 6 different samples of early-type galaxies based on morphology, optical colors, specific star formation rate, a best-fit to the observed spectral energy distribution, and a criterion combining morphological, spectroscopic and photometric informations. The "morphological" sample has the higher percentage of contamination in colors, specific star formation rate and presence of emission lines, while the "pure passive" sample is the purest, with properties mostly compatible with no star formation activity; however, it is also the less economic criterion in terms of information used. The best performing among the other criteria are the "photometric type" and the "sSFR", providing a percentage of contamination only slightly higher than the "pure passive" criterion (on average of a factor of ~2) but with absolute values of the properties of contaminants still compatible with a red, passively evolving population. We also provided two revised definitions of early type galaxies based on restframe color-color and color-mass criteria, that better reproduce the observed bimodalities. The analysis of the number densities shows evidences of mass-assembly downsizing, with galaxies at 10.25View original: http://arxiv.org/abs/1305.1308