X-ray groups of galaxies at 0.5 < z < 1 in zCOSMOS: increased AGN activities in high redshift groups

Masayuki Tanaka,Alexis Finoguenov,S. J. Lilly,M. Bolzonella,C. Marcella Carollo,T. Contini,A. Iovino,Jean-Paul Kneib,F. Lamareille,Olivier Le Fevre,V. Mainieri,V. Presotto,A. Renzini,Marco Scodeggio,J. D. Silverman,Gianni Zamorani,S. Bardelli,A. Bongiorno,K. Caputi,O. Cucciati,Sylvain de la Torre,Loic de Ravel,P. Franzetti,B. Garilli,P. Kampczyk,C. Knobel,K. Kovac,Jean-Francois Le Borgne,Vincent Le Brun,C. Lopez-Sanjuan,C. Maier,M. Mignoli,R. Pello,Y. Peng,E. Perez Montero,L. Tasca,L. Tresse,D. Vergani,Elena Zucca,L. Barnes,R. Bordoloi,A. Cappi,Andrea Cimatti,G. Coppa,Anton M. Koekemoer,H. J. McCracken,M. Moresco,P. Nair,P. A. Oesch,L. Pozzetti,N. Welikala

X-ray groups of galaxies at 0.5 < z < 1 in zCOSMOS: increased AGN activities in high redshift groups

2012

We present a photometric and spectroscopic study of galaxies at 0.5 redshifts from zCOSMOS. We show that the fraction of red galaxies is higher in groups than in the field at all redshifts probed in our study. Interestingly, the fraction of [O II] emitters on the red sequence increases at higher redshifts in groups, while the fraction does not strongly evolve in the field. This is due to increased dusty star-formation activities and/or increased activities of active galactic nuclei (AGNs) in high-redshift groups. We investigate these possibilities using the 30-band photometry and X-ray data. We find that the stellar population of the red [O II] emitters in groups is old, and there is no clear hint of dusty star-formation activities in those galaxies. The observed increase of red [O II] emitters in groups is likely due to increased AGN activities. However, since our overall statistics are poor, any firm conclusions need to be drawn from a larger statistical sample of z similar to 1 groups.

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