Number density as a function of the photometric redshift for the extragalactic sources with a photo-z less than 2 in the entire 3.9 × 4.3   arcmin² region of the sky imaged with GROND (black solid line), for those among them inside the bona fide cluster area (red solid line) or in the surrounding field (blue short-dashed line) – panel a). The analogous distribution functions for the sub-sample of EROs, expected to be at z ~ 1−2 (see text), are also reproduced (panel b)). For the redshift bins 1.0–1.1, 1.2–1.3 and 1.5–1.6, the density of sources within a cluster-centric distance of 1′ exceeds that computed in the adjacent field by a factor of 2. In correspondence of the last two redshift bins, there is a clear excess of EROs.