X-ray selected galaxy clusters behind the Galactic plane

We present the results of the Clusters in the Zone of Avoidance (CIZA) project, which has mapped the large-scale matter distribution behind the Galactic plane by performing the first systematic search for X-ray luminous galaxy clusters at low Galactic latitudes. Previous cluster searches had avoided the Galactic plane due to the severe extinction and stellar obscuration present in the direction of the Milky Way. The approach outlined in this work, namely the use of X-ray emission to locate galaxy clusters, overcomes many of the problems faced by optically selected cluster searches since X-rays do not suffer as severe an extinction in the plane of the Galaxy compared to optical light. Using data from the ROSAT X-ray satellite and follow-up optical observations primarily carried out on the University of Hawaii 2.2 meter telescope, the survey has discovered over 250 galaxy clusters previously hidden by the Milky Way. We have used this sample to examine the distribution of large-scale structures in the Zone of Avoidance and reveal the nature of the Great Attractor region. We have also combined the CIZA sample with existing cluster catalogs covering the sky outside the Zone of Avoidance to create the first all-sky, X-ray selected cluster sample and used this catalog to reassess the origin of the Local Groups's peculiar velocity and ultimately the source of the observed local bulk flow. This work was supported by funding from the NASA Graduate Student Research Program (GSRP).