A Systematic X‐Ray Search for Clusters of Galaxies behind the Milky Way. II. The Second CIZA Subsample

Abstract

We present the latest results of the Clusters in the Zone of Avoidance (CIZA) survey, which is mapping the large-scale matter distribution behind the Milky Way by performing the first systematic search for X-ray luminous galaxy clusters at low Galactic latitudes. The survey's approach, which uses X-ray emission to locate cluster candidates, overcomes the problems faced by optically selected cluster surveys which have traditionally avoided this region of the sky due to the severe extinction present along the Galactic plane. We here present the second flux-limited CIZA cluster catalog containing 60 X-ray luminous galaxy clusters, 88% of which are new discoveries. We also examine the degree to which known superclusters extend into the Zone of Avoidance and highlight newly discovered structures which have previously gone unnoticed. We show that the survey has found far fewer rich clusters in the Great Attractor region than would be expected given the region's proposed mass. Instead, we find a significant increase in the number of clusters behind the Great Attractor, with the most notable being an association of clusters near the Shapley supercluster. We propose these clusters trace an extension of the large-scale filament network in which the Shapley concentration is embedded. We also highlight an association of clusters near the Galactic anticenter, which is the first supercluster found to be completely hidden by the Milky Way. Our finding of a less massive Great Attractor and the detection of significant structures behind the complex supports studies which suggest the motion of nearby galaxies, including that of the Local Group, is due, in part, to a large-scale bulk flow which is induced by overdensities beyond the Great Attractor region.