The zCOSMOS survey: the role of the environment in the evolution of the luminosity function of different galaxy types^*

¹ INAF - Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy e-mail: elena.zucca@oabo.inaf.it
² Laboratoire d'Astrophysique de Marseille, Université d'Aix-Marseille, CNRS, 38 rue Frederic Joliot-Curie, 13388 Marseille Cedex 13, France
³ Institute of Astronomy, Swiss Federal Institute of Technology (ETH Hönggerberg), 8093 Zürich, Switzerland
⁴ INAF - IASF Milano, via Bassini 15, 20133 Milano, Italy
⁵ Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003, USA
⁶ INAF - Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
⁷ Laboratoire d'Astrophysique de Toulouse-Tarbes, Université de Toulouse, CNRS, 14 avenue Edouard Belin, 31400 Toulouse, France
⁸ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
⁹ INAF - Osservatorio Astronomico di Padova, vicolo Osservatorio 5, 35122 Padova, Italy
¹⁰ Max-Planck-Institut für extraterrestrische Physik, 84571 Garching, Germany
¹¹ Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy
¹² INAF - Osservatorio Astronomico di Brera, via Brera 28, 20121 Milano, Italy
¹³ Instituto de Astrofisica de Andalucia, CSIC, Apdo. 3004, 18080 Granada, Spain
¹⁴ Dipartimento di Astronomia, Università di Padova, vicolo Osservatorio 3, 35122 Padova, Italy
¹⁵ INAF - Osservatorio Astronomico di Torino, strada Osservatorio 20, 10025 Pino Torinese, Italy
¹⁶ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MS 21218, USA
¹⁷ LBNL & BCCP, University of California, Berkeley, CA 94720, USA
¹⁸ Centre de Physique Theorique, Marseille, France
¹⁹ Institut d'Astrophysique de Paris, UMR 7095 CNRS, Université Pierre et Marie Curie, 98 bis Boulevard Arago, 75014 Paris, France
²⁰ Universitäts-Sternwarte, Scheinerstrasse 1, 81679 Munich, Germany
²¹ Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany
²² INAF, Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monteporzio Catone, Italy
²³ Canada-France-Hawaii Telescope Corporation, 65-1238 Mamalahoa Hwy, Kamuela, HI 96743, USA
²⁴ AIM Unité Mixte de Recherche CEA CNRS, Université Paris VII UMR 158, Paris, France
²⁵ California Institute of Technology, MC 105-24, 1200 East California Boulevard, Pasadena, CA 91125, USA
²⁶ Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI, 96822, USA
²⁷ Research Center for Space and Cosmic Evolution, Ehime University, Bunkyo-cho, Matsuyama 790-8577, Japan
²⁸ Large Binocular Telescope Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721-0065, USA

Received: 9 June 2009
Accepted: 17 September 2009

Abstract

Aims. An unbiased and detailed characterization of the galaxy luminosity function (LF) is a basic requirement in many astrophysical issues: it is of particular interest in assessing the role of the environment in the evolution of the LF of different galaxy types.

Methods. We studied the evolution in the B band LF to redshift in the zCOSMOS 10k sample, for which both accurate galaxy classifications (spectrophotometric and morphological) and a detailed description of the local density field are available.

Results. The global B band LF exhibits a brightening of ~0.7 mag in M^* from to . At low redshifts (), spectrophotometric late types dominate at faint magnitudes (), while the bright end is populated mainly by spectrophotometric early types. At higher redshift, spectrophotometric late-type galaxies evolve significantly and, at redshift ,the contribution from the various types to the bright end of the LF is comparable. The evolution for spectrophotometric early-type galaxies is in both luminosity and normalization: M^* brightens by ~0.6 mag but decreases by a factor ~1.7 between the first and the last redshift bin. A similar behaviour is exhibited by spectrophotometric late-type galaxies, but with an opposite trend for the normalization: a brightening of ~0.5 mag is present in M^*, while increases by a factor ~1.8.
Studying the role of the environment, we find that the global LF of galaxies in overdense regions has always a brighter M^* and a flatter slope. In low density environments, the main contribution to the LF is from blue galaxies, while for high density environments there is an important contribution from red galaxies to the bright end.
The differences between the global LF in the two environments are not due to only a difference in the relative numbers of red and blue galaxies, but also to their relative luminosity distributions: the value of M^* for both types in underdense regions is always fainter than in overdense environments. These results indicate that galaxies of the same type in different environments have different properties.
We also detect a differential evolution in blue galaxies in different environments: the evolution in their LF is similar in underdense and overdense regions between and , and is mainly in luminosity. In contrast, between and there is little luminosity evolution but there is significant evolution in , that is, however, different between the two environments: in overdense regions increases by a factor ~1.6, while in underdense regions this increase reaches a factor ~2.8. Analyzing the blue galaxy population in more detail, we find that this evolution is driven mainly by the bluest types.

Conclusions. The “specular” evolution of late- and early-type galaxies is consistent with a scenario where a part of blue galaxies is transformed in red galaxies with increasing cosmic time, without significant changes in the fraction of intermediate-type galaxies. The bulk of this tranformation in overdense regions probably happened before , while it is still ongoing at lower redshifts in underdense environments.