Portion (8.25 × 8.25 arcmin²) of the J-band HAWKI image with XMM-Newton X-ray contours overlayed. The field of view of the different instruments used in this work is also shown. The HAWKI J and Ks and ISPI H-band observations cover a field of view much larger than the figure. The FORS2 B-, R- and z-band coverage was obtained from different ESO programs. Most of the X-ray sources are likely distant AGNs, but the extended emission associated with the cluster can be appreciated in the center. The dashed circle marks the R₅₀₀ = 0.75 Mpc radius derived by Rosati et al. (2009). We denote the position of the galaxies analyzed in this study by distinguishing between field and cluster and between those that yielded a V_max value and those that did not.