XMM-LSS discovery of a z = 1.22 galaxy cluster

Creators: Bremer, M. N.; Valtchanov, I.; Willis, J.; Altieri, B.; Andreon, S.; Duc, P. A.; Fang, F.; Jean, C.; Lonsdale, C.; Pacaud, F.; Pierre, M.; Shupe, D. L.; Surace, J. A.; Waddington, I.

Abstract

We present details of the discovery of XLSS J022303.0−043622, a z= 1.2 cluster of galaxies. This cluster was identified from its X-ray properties and selected as a z > 1 candidate from its optical/near-infrared (IR) characteristics in the XMM Large-Scale Structure Survey (XMM-LSS). It is the most distant system discovered in the survey to date. We present ground-based optical and near-IR observations of the system carried out as part of the XMM-LSS survey. The cluster has a bolometric X-ray luminosity of 1.1 ± 0.7 × 10^44 erg s^−1 , fainter than most other known z > 1 X-ray selected clusters. In the optical it has a remarkably compact core, with at least a dozen galaxies inside a 125 kpc radius circle centred on the X-ray position. Most of the galaxies within the core, and those spectroscopically confirmed to be cluster members, have stellar masses similar to those of massive cluster galaxies at low redshift. They have colours comparable to those of galaxies in other z > 1 clusters, consistent with showing little sign of strong ongoing star formation. The bulk of the star formation within the galaxies appears to have ceased at least 1.5 Gyr before the observed epoch. Our results are consistent with massive cluster galaxies forming at z > 1 and passively evolving thereafter. We also show that the system is straightforwardly identified in Spitzer/IRAC 3.6- and 4.5-μm data obtained by the Spitzer Wide-area Infrared Extragalactic (SWIRE) survey emphasizing the power and utility of joint XMM and Spitzer searches for the most distant clusters.

Additional Information

© 2006 The Authors. Journal compilation © 2006 RAS. Accepted 2006 July 4. Received 2006 June 30; in original form 2005 November 4. XMM is an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. This work was based on observations made with ESO Telescopes at the La Silla and Paranal Observatories under programme IDs 70.A-0733 and 074.A-0360 and with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the CFHT which is operated by the National Research Council (NRC) of Canada, the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France and the University of Hawaii. This work is based in part on data products produced at TERAPIX and the Canadian Astronomy Data Centre as part of the CFHTLS, a collaborative project of NRC and CNRS. Support for SWIRE, part of the Spitzer Space Telescope Legacy Science Program, was provided by NASA through an award issued by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. This work was also supported by the European Community RTN Network POE (grant nr. HPRN-CT-2000-00138). MNB acknowledges Leverhulme Trust funding for the early part of this work. SA acknowledges financial contribution from contract ASI-INAF I/023/05/0. We thank Roberto de Propris for useful discussions.

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