EDP Sciences
Free access
Volume 406, Number 3, August II 2003
Page(s) 789 - 795
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20030657

A&A 406, 789-795 (2003)
DOI: 10.1051/0004-6361:20030657

The origin of X-ray emission of two distant ( $\mathsf{\textit{z}\,>1}$) cluster candidates with XMM-Newton

D. M. Neumann1, M. Arnaud1, C. Benoist2, L. da Costa3, H. E. Jørgensen4, L. F. Olsen4, S. Bardelli5, E. Zucca5, S. Arnouts6, A. Biviano

7 and M. Ramella7

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

(Received 18 March 2003 / Accepted 14 April 2003 )

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 z=1.2-1.7. is a rich system ( $\Lambda_{\rm cl}=299$), with a spectroscopically confirmed redshift of z=1.3. Both galaxy concentrations show firm X-ray detections, located within $30^{\prime\prime}$ 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 14 h65-1 kpc and 40 h65-1 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 ~ $ 0.7{-}2.1 \times 10^{44}~{h_{65}^{-2}}$ erg/s for , depending on the exact redshift. For the limit is $L_{\rm
bol}= (6.2\pm1.4) \times 10^{43}~{h_{65}^{-2}}$  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.

Key words: cosmology: observations -- cosmology: large-scale structure of Universe -- galaxies: clusters: individual: , -- X-rays: galaxies: clusters -- galaxies: active

Offprint request: D. M. Neumann, ddon@cea.fr

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