The XMM-LSS survey^*

First high redshift galaxy clusters: Relaxed and collapsing systems

¹ CEA/Saclay, Service d'Astrophysique, 91191, Gif-sur-Yvette, France e-mail: i.valtchanov@imperial.ac.uk
² Astrophysics Group, Blackett Laboratory, Imperial College, London SW7 2BW, UK
³ ESO, Ave. Alonso de Cordova 3107, Casilla 19, Santiago 19001, Chile
⁴ School of Physics and Astronomy, University of Birmingham, Birmingham, UK
⁵ INAF – Osservatorio Astronomico di Brera, via Brera 28, 20121 Milano, Italy
⁶ LAM, Traverse du Siphon, 13012 Marseille, France
⁷ ESA, Villafranca del Castillo, Spain
⁸ Istituto di Astrofisica Spaziale e Fisica Cosmica, Sezione di Milano, via Bassini 15, 20133 Milano
⁹ Department of Physics, University of Bristol, H.H. Wills Laboratory, Bristol, UK
¹⁰ Université de Liège, Allée du 6 Août, 17, B5C, 4000 Sart Tilman, Belgium

Received: 2 May 2003
Accepted: 5 May 2004

Abstract

We present five newly found galaxy clusters at from the XMM Large-Scale Structure Survey (XMM-LSS). All five objects are extended X-ray sources in the XMM images. For three of them we have sufficient spectroscopically confirmed member galaxies that an estimate of the velocity dispersion is possible: XLSSC 001 at and  km s^-1, XLSSC 002 at and  km s^-1 and XLSSC 003 at and  km s^-1. These three clusters have X-ray bolometric luminosities  erg s^-1 and temperatures  keV, and consequently are less massive than previously known clusters at similar redshifts, but nevertheless they follow the low redshift scaling relations between  and , within the limits of the measurement errors. One of the clusters, XLSSC 004, is detected independently as an overdensity of galaxies of a colour that matches the redshift of the central galaxy , although it cannot unambiguously be confirmed by the spectroscopic observations alone. The highest redshift candidate cluster pertaining to this paper, XLSSC 005, is most likely a double cluster complex at a redshift around unity, associated with an extended X-ray source with probable substructure.