Cluster galaxies in XMMU J2235-2557: galaxy population properties in most massive environments at z  ~  1.4^⋆

¹ National Radio Astronomy Observatory, 1003 Lopezville Rd., Socorro, NM, 87801 USA
e-mail: vstrazzu@nrao.edu
² European Southern Observatory, Karl Schwarzschild Strasse 2, 85748 Garching bei Muenchen, Germany
³ CEA, Laboratoire AIM-CNRS-Université Paris Diderot, Irfu/SAp, Orme des Merisiers, 91191 Gif-sur-Yvette, France
⁴ INAF-Osservatorio Astronomico di Trieste, via Tiepolo 11, 34131 Trieste, Italy
⁵ Department of Astronomy, Universidad de Concepción. Casilla 160-C, Concepción, Chile
⁶ Australian Astronomical Observatory, PO Box 296, Epping, NSW 1710, Australia
⁷ Institute for the Physics and Mathematics of the Universe, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa-shi, Chiba 277-8583, Japan
⁸ Wells Fargo Bank, 4525 Sharon Road, Charlotte, NC 28211, USA
⁹ Department of Physics and Astronomy, University of California, Riverside, CA 92521, USA
¹⁰ Department of Physics, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA
¹¹ Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany
¹² Universitäts-Sternwarte, Scheinerstrasse 1, Munich 81679, Germany
¹³ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
¹⁴ Astronomy Department, University of California, Santa Cruz, CA 95064, USA
¹⁵ Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112, USA
¹⁶ Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Berkeley, CA 94720, USA
¹⁷ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA

Received: 21 June 2010
Accepted: 29 August 2010

Abstract

We present a multi-wavelength study of galaxy populations in the core of the massive, X-ray luminous cluster XMMU J2235 at z = 1.39, based on high quality VLT and HST photometry at optical and near-infrared wavelengths.

We derive luminosity functions in the z, H, and K_s bands, approximately corresponding to restframe U, R and z band. These show a faint-end slope consistent with being flat, and a characteristic magnitude M^∗ close to passive evolution predictions of M^∗ of local massive clusters, with a formation redshift z > 2.

The color − magnitude and color-mass diagrams show evidence of a tight red sequence (intrinsic scatter  ≲ 0.08) of massive galaxies already in place, with overall old stellar populations and generally early-type morphology. Beside the red colors, these massive (>6 × 10¹⁰   M_⊙) galaxies typically show early-type spectral features, and rest-frame far-UV emission consistent with very low star formation rates (SFR < 0.2   M_⊙ yr^-1).

Star forming spectroscopic members, with SFR of up to  ~100 M_⊙/yr, are all located at clustercentric distances  ≳ 250 kpc, with the central cluster region already appearing effectively quenched. Most part of the cluster galaxies more massive than 6 × 10¹⁰   M_⊙ within the studied area do not appear to host significant levels of star formation.

The high-mass end of the galaxy populations in the core of this cluster appears to be in a very advanced evolutionary stage, not only in terms of formation of the stellar populations, but also of the assembly of the stellar mass. The high-mass end of the galaxy stellar mass function is essentially already in place. The stellar mass fraction estimated within r₅₀₀ (~1%, Kroupa IMF) is already similar to that of local massive clusters.

On the other hand, surface brightness distribution modeling of the massive red sequence galaxies may suggest that their size is often smaller than expected based on the local stellar mass vs. size relation. An evolution of the stellar mass vs. size relation might imply that, in spite of the overall early assembly of these sources, their evolution is not complete, and processes like minor (and likely dry) merging might still shape the structural properties of these objects to resemble those of their local counterparts, without substantially affecting their stellar mass or host stellar populations. Nonetheless, a definite conclusion on the actual relevance of size evolution for the studied early-type sample is precluded by possible systematics and biases.