The 10k zCOSMOS: morphological transformation of galaxies in the group environment since z~1

K. Kovac (1) , S. J. Lilly (1) , C. Knobel (1) , M. Bolzonella (2) , A. Iovino (1) , C. M. Carollo (3) , C. Scarlata (1) , M. Sargent , O. Cucciati (4) , G. Zamorani (1) , L. Pozzetti (5) , L. A. M. Tasca (6) , M. Scodeggio (7) , P. Kampczyk (1) , Y. Peng (8) , P. Oesch (1) , E. Zucca (9) , A. Finoguenov (10) , T. Contini (11) , J. -P. Kneib (11) , O. Le Fevre (6) , V. Mainieri (1) , A. Renzini (1) , S. Bardelli (5) , A. Bongiorno (2) , K. Caputi (1) , G. Coppa (1) , S. de La Torre (1) , L. de Ravel (1) , P. Franzetti (1) , B. Garilli (1) , F. Lamareille (11) , J. -F. Le Borgne (12) , V. Le Brun (6) , C. Maier (1) , M. Mignoli (1) , R. Pello (11) , E. Perez Montero (13) , E. Ricciardelli (1) , J. D. Silverman (1) , M. Tanaka (14) , L. Tresse (6) , D. Vergani (15) , U. Abbas (1) , D. Bottini (1) , A. Cappi (16) , P. Cassata (1) , Alessandro Cimatti (1) , M. Fumana (1) , L. Guzzo (1) , A. M. Koekemoer (17) , A. Leauthaud (6) , D. Maccagni (1) , Christian Marinoni (18, 19) , H. J. Mccracken (20) , P. Memeo (1) , B. Meneux (6) , C. Porciani (1) , R. Scaramella (1) , N. Z. Scoville (21)

1 AUTRES
2 UNIBO - Alma Mater Studiorum Università di Bologna = University of Bologna
3 University of Chicago
4 Dipartimento di Fisica
5 OABO - INAF - Osservatorio Astronomico di Bologna
6 LAM - Laboratoire d'Astrophysique de Marseille
7 INAF- Milano
8 Institute of Astronomy [ETH Zürich]
9 OAB - INAF - Osservatorio Astronomico di Brera
10 MPIA - Max-Planck-Institut für Astronomie
11 LATT - Laboratoire Astrophysique de Toulouse-Tarbes
12 LATT - Laboratoire d'Astrophysique de l'Observatoire Midi-Pyrénées
13 Glycosciences Laboratory
14 Tokai University
15 OAA - INAF - Osservatorio Astrofisico di Arcetri
16 IASF-Bo - Istituto di Astrofisica Spaziale e Fisica cosmica - Bologna
17 STSci - Space Telescope Science Institute
18 CPT - Centre de Physique Théorique - UMR 6207
19 CPT - Centre de Physique Théorique - UMR 7332
20 IAP - Institut d'Astrophysique de Paris
21 CALTECH - California Institute of Technology

We study the evolution of galaxies inside and outside of the group environment since z=1 using a large well defined set of groups and galaxies from the zCOSMOS-bright redshift survey in the COSMOS field. The fraction of galaxies with early-type morphologies increases monotonically with M_B luminosity and stellar mass and with cosmic epoch. It is higher in the groups than elsewhere, especially at later epochs. The emerging environmental effect is superposed on a strong global mass-driven evolution, and at z~0.5 and log(M*/Msol)~10.2, the "effect" of group environment is equivalent to (only) about 0.2 dex in stellar mass or 2 Gyr in time. The stellar mass function of galaxies in groups is enriched in massive galaxies. We directly determine the transformation rates from late to early morphologies, and for transformations involving colour and star formation indicators. The transformation rates are systematically about twice as high in the groups as outside, or up to 3-4 times higher correcting for infall and the appearance of new groups. The rates reach values, for masses around the crossing mass 10^10.5 Msol, as high as (0.3-0.7)/Gyr in the groups, implying transformation timescales of 1.4-3 Gyr, compared with less than 0.2/Gyr, i.e. timescales >5 Gyr, outside of groups. All three transformation rates decrease at higher stellar masses, and must decrease also at the lower masses below 10^10 Msol which we cannot well probe. The rates involving colour and star formation are consistently higher than those for morphology, by a factor of about 50%. Our conclusion is that the transformations which drive the evolution of the overall galaxy population since z~1 must occur at a rate 2-4 times higher in groups than outside of them.

Domaines: Cosmologie et astrophysique extra-galactique [astro-ph.CO]

K. Kovac, S. J. Lilly, C. Knobel, M. Bolzonella, A. Iovino, et al.. The 10k zCOSMOS: morphological transformation of galaxies in the group environment since z~1. The Astrophysical Journal, 2010, 718 (1), pp.86. ⟨10.1088/0004-637X/718/1/86⟩. ⟨hal-00421830⟩