An extension of the SHARC survey ^*,**

¹ LAM, Traverse du Siphon, 13012 Marseille, France e-mail: christophe.adami@oamp.fr
² Department Physics & Astronomy, Northwestern University, Evanston, IL 60208-2900, USA
³ Institut d'Astrophysique de Paris, CNRS, UMR 7095, Université Pierre et Marie Curie, 98bis Bd Arago, 75014 Paris, France
⁴ Observatoire de Paris, LERMA, 61 Av. de l'Observatoire, 75014 Paris, France
⁵ INAF - Osservatorio Astronomico di Capodimonte, Naples, Italy
⁶ Department of Physics and Astronomy, University College London, London WC1E 6BT, UK
⁷ UCO/Lick Observatory, University of California, Santa Cruz, CA 95064, USA
⁸ University of Chicago, Department of Astronomy and Astrophysics, 5640 South Ellis Avenue, Chicago, IL 60637, USA
⁹ Instituto de Astronomia, Geofísica e C. Atmosf./USP, R. do Matão 1226, 05508-090 São Paulo/SP, Brazil
¹⁰ Astronomy Centre, University of Sussex, Falmer, Brighton BN1 9QJ, UK
¹¹ Department of Astronomy, National Center for Supercomputing Applications, University of Illinois, Urbana-Champaign, 1002 W. Green, Urbana, IL 61801, USA

Received: 6 February 2007
Accepted: 30 May 2007

Abstract

Aims.We report on our search for distant clusters of galaxies based on optical and X-ray follow up observations of X-ray candidates from the SHARC survey, and based on the assumption that the absence of bright optical or radio counterparts to possibly extended X-ray sources could mean that they are distant clusters.

Methods.We have obtained deep optical images and redshifts for several of these objects and analyzed archive XMM-Newton or Chandra data where applicable.

Results.In our list of candidate clusters, two are probably galaxy structures at redshifts of 0.51 and 0.28. Seven other structures are possibly galaxy clusters between 0.3 and 1. Three sources are identified with QSOs and are thus likely to be X-ray point sources, and six more also probably fall in this category. One X-ray source is spurious or variable. For 17 other sources, the data are too sparse at this time to put forward any hypothesis on their nature. We also serendipitously detected a cluster at and another galaxy concentration which is probably a structure with a redshift in the [ 0.15-0.6] range.

Conclusions.We discuss these results within the context of future space missions to demonstrate the necessity of a wide field of view telescope optimized for the 0.5-2 keV range.