The origin of X-ray emission of two distant ($\mathsf{\textit{z}\,>1}$) cluster candidates with XMM-Newton

We present here a study of data of two distant galaxy cluster candidates. One of these was discovered serendipitously in near infrared data, CL J0533-2411, the other one corresponds to the cluster EIS J0533-2412 part of the EIS cluster survey. The estimated redshift of is . is a rich system (), with a spectroscopically confirmed redshift of . Both galaxy concentrations show firm X-ray detections, located within of their optical center. However, we cannot resolve the sources with . If the X-ray emission originates from the X-ray emitting intra-cluster medium (ICM) it would be extremely concentrated which is rather unlikely (core radii below kpc and kpc, respectively). We argue that the X-ray sources are more likely AGN members of the galaxy concentrations. We set an upper limit for the bolometric luminosity of a hot ICM in the range ~ erg/s for , depending on the exact redshift. For the limit is erg/s. We interpret our result in the following way: (and possibly ) are proto-clusters and show matter overdensities before collapse, which explains the low significance of extended X-ray emission.