Batch discovery of nine z ∼ 1 clusters using X-ray and K or R, z′ images

We present the results of an initial search for clusters of galaxies at z similar to 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 similar to 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) similar to 0-8, 1.0 and 1.3. The present sample significantly increases the number of such clusters. The measured density of z I clusters, after discarding 'low'-redshift systems at z less than or similar to 0.92 is about 1.7 deg(-2) (with 68 per cent confidence interval equal to [1.0, 2.9]) for f(x) greater than or similar to 2.5 10(-15) erg cm(-2) s(-1) ([0.5-2] keV) and this is a lower limit, having, screened not all potential z similar to 1 candidate clusters. Coordinates, X-ray measures and evidence for nine X-ray-selected high-redshift clusters is given.