A z = 0.9 Supercluster of X-Ray Luminous, Optically Selected, Massive Galaxy Clusters

Abstract

We report the discovery of a compact supercluster structure at . The structure comprises three optically z p 0.9 selected clusters, all of which are detected in X-rays and spectroscopically confirmed to lie at the same redshift. The Chandra X-ray temperatures imply individual masses of ∼ M,. The X-ray masses are consistent 14 5 # 10 with those inferred from optical–X-ray scaling relations established at lower redshift. A strongly lensed z ∼ 4 Lyman break galaxy behind one of the clusters allows a strong-lensing mass to be estimated for this cluster, which is in good agreement with the X-ray measurement. Optical spectroscopy of this cluster gives a dynamical mass in good agreement with the other independent mass estimates. The three components of the RCS 231900 supercluster are separated from their nearest neighbor by a mere !3 Mpc in the plane of the sky and likely !10 Mpc along the line of sight, and we interpret this structure as the high-redshift antecedent of massive (∼10 15 M ) clusters such as MS 0451.50305. z ∼ 0.5