The near-infrared luminosity function of cluster galaxies beyond redshift one

¹ Dipartimento di Scienze Fisiche, Università degli Studi di Napoli “Federico II”, via Cinthia, 80126 Napoli, Italy e-mail: vstrazzu@eso.org; strazzul@na.astro.it
² European Southern Observatory, Karl-Scwarzchild-Strasse 2, 85748 Garching, Germany
³ Department of Physics, University of California at Davis, 1 Shields Avenue, Davis, CA 95616, USA
⁴ Institute of Geophysics and Planetary Physics, LLNL, Livermore, CA 94551, USA
⁵ European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Santiago, Chile
⁶ Instituto Nazionale di Astrofisica, Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 34131 Trieste, Italy
⁷ Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles Str., Baltimore, MD 21218, USA
⁸ Jet Propulsion Laboratory, California Institute of Technology, MC 169–327, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
⁹ Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
¹⁰ Max-Planck-Institut für extraterrestrische Physik, Postfach 1319, 85748 Garching, Germany
¹¹ Department of Astronomy, Yale University, PO Box 208101, New Haven, CT 06520–8101, USA

Received: 11 October 2005
Accepted: 16 January 2006

Abstract

Aims.We determined the K_s band luminosity function (LF), and inferred the corresponding stellar mass function, of cluster galaxies at redshift , using near-infrared images of three X-ray luminous clusters at .

Methods.The composite LF was derived down to , by means of statistical background subtraction, and is well described by a Schechter function with and . Using available X-ray mass profiles we determined the M/L ratios of these three clusters, which tend to be lower than those measured in the local universe. Finally, from the K_s band composite LF we derived the stellar mass function of cluster galaxies.

Results.With these data, no significant difference can be seen between the cluster galaxies LF and the LF of field galaxies at similar redshift. We also found no significant evolution out to in the bright (<) part of the LF probed in this study, apart from a brightening of  mag of the characteristic magnitude of the high redshift LF. We confirm, and extend to higher redshift, the result from previous work that the redshift evolution of the characteristic magnitude M^* is consistent with passive evolution of a stellar population formed at .

Conclusions.The results obtained in this work support and extend previous findings that most of the stars in bright galaxies were formed at high redshift, and that K_s-bright () galaxies were already in place at , at least in the central regions of X-ray luminous clusters. Together with recent results on the field galaxy stellar mass function, this implies that most of the stellar mass is already assembled in massive galaxies by , both in low and high density environments.