2008A&A...481L..73F

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. We present details of the newly-discovered galaxy cluster XMMUJ0104.4-0630 at z=0.947 and a probable associated system in the LSS environment. 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. We find a well-evolved, intermediate luminosity cluster with L^0.5–2.0keV_X=(6.4±1.3)x10⁴³h^–2₇₀erg/s and strong central 1.4GHz 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 1-2Gyr for a single burst solar metallicity model. The second, less evolved X-ray cluster at a projected distance of 6.4' (∼3Mpc) 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.