The XMM Cluster Survey: optical analysis methodology and the first data release

The XMM Cluster Survey (XCS) is a serendipitous search for galaxy clusters using all publicly available data in the XMM–Newton Science Archive. Its main aims are to measure cosmological parameters and trace the evolution of X-ray scaling relations. In this paper we present the first data release from the XMM Cluster Survey (XCS-DR1). This consists of 503 optically confirmed, serendipitously detected, X-ray clusters. Of these clusters, 256 are new to the literature and 357 are new X-ray discoveries. We present 463 clusters with a redshift estimate (0.06 T X ) for 401 clusters (0.4 T X 1.0, including a new spectroscopically confirmed cluster at ɀ = 1.01); (ii) 66 clusters with high T X (>5 keV); (iii) 130 clusters/groups with low T X ( T X values in the Sloan Digital Sky Survey (SDSS) ‘Stripe 82’ co-add region; (v) 77 clusters with measured T X values in the Dark Energy Survey region; (vi) 40 clusters detected with sufficient counts to permit mass measurements (under the assumption of hydrostatic equilibrium); (vii) 104 clusters that can be used for applications such as the derivation of cosmological parameters and the measurement of cluster scaling relations. The X-ray analysis methodology used to construct and analyse the XCS-DR1 cluster sample has been presented in a companion paper, Lloyd-Davies et al.