The origin of X-ray emission of two distant () cluster candidates with XMM-Newton

¹ CEA/Saclay DSM/DAPNIA/SAp, L'Orme des Merisiers, 91191 Gif-sur-Yvette, France
² Observatoire de la Côte d'Azur, CERGA, BP 4229, 06304 Nice Cedex 4, France
³ ESO, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
⁴ Astronomical Observatory, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
⁵ INAF – Osservatorio Astronomico di Bologna via Ranzani 1, 40127 Bologna, Italy
⁶ Laboratoire d'Astrophysique de Marseille, Traverse du Siphon – BP 8, 13376 Marseille Cedex 12, France
⁷ INAF – Osservatorio Astronomico di Trieste via G.B. Tiepolo 11, 34131 Trieste, Italy


Corresponding author: D. M. Neumann, ddon@cea.fr

Received: 18 March 2003
Accepted: 14 April 2003

Abstract

We present here a study of  data of two distant galaxy cluster candidates. One of these was discovered serendipitously in near infrared data, CL J0533-2411, the other one corresponds to the cluster EIS J0533-2412 part of the EIS cluster survey. The estimated redshift of  is .  is a rich system (), with a spectroscopically confirmed redshift of . Both galaxy concentrations show firm X-ray detections, located within of their optical center. However, we cannot resolve the sources with . If the X-ray emission originates from the X-ray emitting intra-cluster medium (ICM) it would be extremely concentrated which is rather unlikely (core radii below kpc and kpc, respectively). We argue that the X-ray sources are more likely AGN members of the galaxy concentrations. We set an upper limit for the bolometric luminosity of a hot ICM in the range ~ erg/s for , depending on the exact redshift. For  the limit is erg/s. We interpret our result in the following way:  (and possibly ) are proto-clusters and show matter overdensities before collapse, which explains the low significance of extended X-ray emission.