  We present here a study of XMM-Newton 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 CL J0533-2411 is z=1.2-1.7.
EIS J0533-2412 is a rich system (Lambda_cl=299), with a spectroscopically
confirmed redshift of z=1.3. Both galaxy concentrations show firm X-ray
detections, located within 30" of their optical center. However, we cannot
resolve the sources with XMM-Newton. 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 14 h_{65}^{-1}kpc and 40
h_{65}^{-1}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 ~0.7-2.1 10^{44}
h_{65}^{-2}erg/s for CL J0533-2411, depending on the exact redshift. For EIS
J0533-2412 the limit is L_bol=(6.2+/-1.4) 10^{43} h_{65}^{-2}erg/s. We
interpret our result in the following way: EIS J0533-2412 (and possibly CL
J0533-2411) are proto-clusters and show matter overdensities before collapse,
which explains the low significance of extended X-ray emission.

Astrophysics