2005MNRAS.359.1250A

We present the results of an initial search for clusters of galaxies at z∼ 1 and above, using data from 2.9 square degrees of XMM-Newton images. By selecting weak potentially extended X-ray sources with faint or no identifications in deep, ground-based optical imaging, we have constructed a starting sample of 19 high-redshift cluster candidates. Near-IR and R, z' imaging of these fields identified nine of them as high-redshift systems. Six of these were confirmed spectroscopically, three at z∼ 1.0 and the other three in the 0.8 < z < 0.92 range. The remaining three systems have solid photometric evidence to be at z_phot∼ 0.8, 1.0 and 1.3. The present sample significantly increases the number of such clusters. The measured density of z≳ 1 clusters, after discarding `low'-redshift systems at z≲ 0.92 is about 1.7/deg2 (with 68 per cent confidence interval equal to [1.0, 2.9]) for f_X≳ 2.5 10^–15 erg/cm2/s ([0.5-2] keV) and this is a lower limit, having screened not all potential z∼ 1 candidate clusters. Coordinates, X-ray measures and evidence for nine X-ray-selected high-redshift clusters is given.