Scaling relations of the colour – detected cluster RzCS 052 at z = 1 . 016 and some other high redshift clusters

We report on the discovery of the z = 1.016 cluster RzCS 052 using a modified red sequence method, followup spectroscopy and X-ray imaging. This cluster has a velocity dispersion of 710 ± 150 km s, a virial mass of 4.0 × 10 M⊙ (based on 21 spectroscopically confirmed members) and an X-ray luminosity of (0.68± 0.47)× 10 ergs s in the [1-4] keV band. This optically selected cluster appears to be of richness class 3 and to follow the known LX − σv relation for high redshift Xray selected clusters. Using these data, we find that the halo occupation number for this cluster is only marginally consistent with what expected assuming a self-similar evolution of cluster scaling relations, suggesting perhaps a break of them at z ∼ 1. We also rule out a strong galaxy merging activity between z = 1 and today. Finally, we present a Bayesian approach to measuring cluster velocity dispersions and X-ray luminosities in the presence of a background: we critically reanalyze recent claims for X-ray underluminous clusters using these techniques and find that the clusters can be accommodated within the existing LX − σv relation.