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

Abstract

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 < z < 1.46), including 261 clusters with spectroscopic redshifts. The remainder have photometric redshifts. In addition, we have measured X‐ray temperatures ( T X ) for 401 clusters (0.4 < T X < 14.7 keV). We highlight seven interesting subsamples of XCS‐DR1 clusters: (i) 10 clusters at high redshift ( z > 1.0, including a new spectroscopically confirmed cluster at z = 1.01); (ii) 66 clusters with high T X (>5 keV); (iii) 130 clusters/groups with low T X (<2 keV); (iv) 27 clusters with measured 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.