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

We present the latest results of the Clusters in the Zone of Avoidance (CIZA) survey, which is mapping large-scale structures behind the Milky Way by performing the first systematic search for galaxy clusters at low Galactic latitudes. The survey's approach, which uses X-ray emission to locate cluster candidates, minimizes 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 57 X-ray-selected galaxy clusters, of which 88% are new discoveries. We use this sample to examine the degree to which known large-scale structures extend into the zone of avoidance and highlight newly discovered structures that have previously gone unnoticed. We note that the CIZA survey has thus far found 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 that 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 form the first supercluster found to be completely hidden by the Milky Way. Our preliminary findings of a less massive Great Attractor and the detection of significant structures behind the complex support studies that suggest the motion of nearby galaxies is due, in part, to a large-scale bulk flow, which is induced by overdensities beyond the Hydra-Centaurus region.