Free access article

A&A 503, 399-408 (2009)
DOI: 10.1051/0004-6361/200811021

Cluster and cluster galaxy evolution history from IR to X-ray observations of the young cluster RX J1257.2+4738 at z = 0.866

M. P. Ulmer^{1, 2}, C. Adami¹, G. B. Lima Neto³, F. Durret⁴, G. Covone⁵, O. Ilbert^{1, 6}, E. S. Cypriano^{3, 7}, S. S. Allam⁸, R. G. Kron⁹, W. A. Mahoney¹⁰, and R. Gavazzi<sup>4

1</sup>  LAM, Pôle de l'Etoile Site Château-Gombert, 38 rue Frédéric Juliot-Curie, 13388 Marseille Cedex 13, France
    e-mail: christophe.adami@oamp.fr
²  Department of Physics and Astronomy, Northwestern University, 2131 Sheridan Road, Evanston IL 60208-2900, USA
³  Instituto de Astronomia, Geofísica e C. Atmosf./USP, R. do Matão 1226, 05508-090 São Paulo/SP, Brazil
⁴  Institut d'Astrophysique de Paris, CNRS, UMR 7095, Université Pierre et Marie Curie, 98bis Bd Arago, 75014 Paris, France
⁵  Università di Napolia “Federico II”, Dipartimento di Sciennze Fisiche and INAF – Observatorio Astronomico di Capodimonte, v. Moiariello 16, 80131 Napoli, Italy
⁶  Institute for Astronomy, 2680 Woodlawn Dr., University of Hawaii, Honolulu, Hawaii 96822, USA
⁷  Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
⁸  Fermi National Accelerator Laboratory, MS 127, PO Box 500, Batavia, IL 60510, USA
⁹  University of Chicago, Department of Astronomy and Astrophysics, 5640 South Ellis Avenue, Chicago, IL 60637, USA
¹⁰  California Institute of Technology, Spitzer Science Center, MS 314-6, 1200 East California Blvd, Pasadena, CA 91125, USA

Received 23 September 2008 / Accepted 30 June 2009

Abstract
Context. The cosmic time around the z ~ 1 redshift range appears crucial in the cluster and galaxy evolution, since it is probably the epoch of the first mature galaxy clusters. Our knowledge of the properties of the galaxy populations in these clusters is limited because only a handful of z ~ 1 clusters are presently known.
Aims. In this framework, we report the discovery of a z ~ 0.87 cluster and study its properties at various wavelengths.
Methods. We gathered X-ray and optical data (imaging and spectroscopy), and near and far infrared data (imaging) in order to confirm the cluster nature of our candidate, to determine its dynamical state, and to give insight on its galaxy population evolution.
Results. Our candidate structure appears to be a massive z ~ 0.87 dynamically young cluster with an atypically high X-ray temperature as compared to its X-ray luminosity. It exhibits a significant percentage (~90%) of galaxies that are also detected in the 24 m band.
Conclusions. The cluster RXJ1257.2+4738 appears to be still in the process of collapsing. Its relatively high temperature is probably the consequence of significant energy input into the intracluster medium besides the regular gravitational infall contribution. A significant part of its galaxies are red objects that are probably dusty with on-going star formation.

Key words: galaxies: clusters: individual: RX J1257.2+4738 -- galaxies: clusters: general -- Galaxy: evolution

© ESO 2009

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