2XMM J083026+524133: the most X-ray luminous cluster at redshift 1

Abstract

Aims. In the distant universe X-ray luminous clusters of galaxies are rare objects. Large area surveys are therefore needed to probe the high luminosity end of the cluster population at redshifts z > 1. Methods. We correlated extended X-ray sources from the second XMM-Newton source catalogue (2XMM) with the SDSS in order to identify new clusters of galaxies. Distant cluster candidates in empty SDSS fields were imaged in the r -a ndz-bands with the Large Binocular Telescope. We extracted the X-ray spectra of the cluster candidates and fitted thermal plasma models to the data. Results. We determined the redshift 0.99 ± 0.03 for 2XMM J083026.2+524133 from its X-ray spectrum. With a bolometric luminosity of 1.8 × 10 45 erg s −1 this is the most X-ray luminous cluster at redshifts z ≥ 1. We measured a gas temperature of 8.2 ± 0. 9k eV and estimate a cluster mass M500 = 5.6 × 10 14 M� . The optical imaging revealed a rich cluster of galaxies.