The XMM-Newton Distant Cluster Project is a serendipitous survey for clusters of galaxies at redshifts z>=0.8 based on deep archival XMM-Newton observations. ... Low-significance candidate high-z clusters are followed up with the seven-channel imager
GROND (Gamma-Ray Burst Optical and Near-Infrared Detector) that is mounted at a 2m-class telescope. ... The test case is XMMU J0338.7+0030, suggested to be at z~1.45+/-0.15 from the analysis of the z-H vs H colour-magnitude diagram obtained from the follow-up imaging. Later VLT-FORS2 spectroscopy enabled us to identify four members, which set this cluster at z=1.097+/-0.002. To reach a better knowledge of its galaxy population, we observed XMMU J0338.7+0030 with GROND for about 6 hr. The publicly available photo-z code le Phare was used. The Ks-band number counts of the non-stellar sources out of the 832 detected down to z~26 AB-mag in the 3.9x4.3 square arcmin region of XMMU J0338.7+0030 imaged at all GROND bands clearly exceed those computed in deep fields/survey areas at ~20.5 - 22.5 AB-mag. The photo-zs of the three imaged spectroscopic members yield z=1.12+/-0.09. The spatial distribution and the properties of the GROND sources with a photo-z in the range 1.01 - 1.23 confirm the correspondence of the X-ray source with a galaxy over-density at a significance of at least 4.3 sigma. Candidate members that are spectro-photometrically classified as elliptical galaxies define a red locus in the i-z vs z colour-magnitude diagram that is consistent with the red sequence of the cluster RDCS J0910+5422 at z=1.106. XMMU J0338.7+0030 hosts also a population of bluer late-type spirals and irregulars. The starbursts among the photometric members populate both loci, consistently with previous results. The analysis of the available data set indicates that XMMU J0338.7+0030 is a low-mass cluster (M_200 ~ 1E14 M_sun) at z=1.1. (Abridged)
[Abridged] We searched for diffuse stellar emission around BCGs in three of the most X-ray luminous clusters found at z~0.3 in the REFLEX cluster survey and observed with XMM-Newton. These systems (RXCJ0014.3-3022, RXCJ0232.2-4420, and RXCJ2308.3-021
1) are in different dynamical states, as witnessed by their X-ray morphology and optical appearence (e.g. multiplicity of BCGs). [Abridged] Diffuse stellar emission is robustly detected down to a surface brightness of 26 R-mag/arcsec^2 (observed frame) around a total of seven BCGs, extending up to galactocentric distances of ~100 kpc. In particular, it surrounds a pair of BCGs in RXCJ0232.2-4420, while it bridges two BCGs associated with the minor subcomponent of the merging cluster RXCJ0014.3-3022. The diffuse light detected at the greatest distances from the BCGs of the rather regular clusters RXCJ0232.2-4420 and RXCJ2308.3-0211 follows the ICM distribution. Its B-R colour is consistent with the colours measured within the BCG effective radii. The diffuse light around the two pairs of BCGs in RXCJ0014.3-3022 exhibits bluer colours than the BCG central regions by up to 0.5 mag. If the contribution of the intracluster light (ICL) to the detected diffuse light around BCGs is not negligible, ICL and BCGs have similar stellar populations in relatively relaxed clusters. Merging on a cluster scale eventually adds gravitational stresses to BCGs and other galaxies in subcluster cores. This event may affect the properties of the diffuse stellar emission around BCGs. Shredding of star-forming, low-metallicity dwarf galaxies is favoured as the cause of the bluer B-R colours of the diffuse stellar component around the two pairs of BCGs in the merging cluster RXCJ0014.3-3022.
