Indications for 3 Mpc-scale large-scale structure associated with an X-ray luminous cluster of galaxies at z = 0.95

Context: X-ray luminous clusters of galaxies at z ~ 1 are emerging as major cosmological probes and are fundamental tools to study the cosmic large-scale structure and environmental effects of galaxy evolution at large look-back times.
Aims: We present details of the newly-discovered galaxy cluster XMMU J0104.4-0630 at z = 0.947 and a probable associated system in the LSS environment.
Methods: The clusters were found in a systematic study for high-redshift systems using deep archival XMM-Newton data for the serendipitous detection and the X-ray analysis, complemented by optical/near-infrared (NIR) imaging observations and spectroscopy of the main cluster.
Results: We find a well-evolved, intermediate luminosity cluster with L^{0.5-2.0 keV}_X = (6.4± 1.3) × 10⁴³ h^-2₇₀ erg s^-1 and strong central 1.4 GHz radio emission. The cluster galaxy population exhibits a pronounced transition toward bluer colors at cluster-centric distances of 1-2 core radii, consistent with an age difference of 1-2 Gyr for a single burst solar metallicity model. The second, less evolved X-ray cluster at a projected distance of 6.4´ (~3 Mpc) and a concordant red-sequence color likely forms a cluster-cluster bridge with the main target as part of its surrounding large-scale structure at z ≃ 0.95.

Based on observations obtained with ESO Telescopes at the Paranal Observatory under programme ID 72.A-0706 and 275.A-5059, and observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).