The Dipole Anisotropy of the First All-Sky X-Ray Cluster Sample

We combine the recently published CIZA (clusters in the zone of avoidance) galaxy cluster catalog with the XBAC (X-ray-brightest Abell-type cluster) sample to produce the first all-sky catalog of X-ray clusters, in order to examine the origins of the Local Group's peculiar velocity without the use of reconstruction methods to fill the traditional zone of avoidance. The advantages of this approach are (1) X-ray-emitting clusters tend to trace the deepest potential wells and therefore have the greatest effect on the dynamics of the Local Group, and (2) our all-sky sample provides data for nearly a quarter of the sky that is largely incomplete in optical cluster catalogs. We find that the direction of the Local Group's peculiar velocity is well aligned with the cosmic microwave background (CMB) as early as the Great Attractor region 40 h-1 Mpc away, but that the amplitude of its dipole motion is largely set between 140 and 160 h-1 Mpc. Unlike previous studies using galaxy samples, we find that without Virgo included, ~70% of our dipole signal comes from mass concentrations at large distances (>60 h-1 Mpc) and does not flatten, indicating isotropy in the cluster distribution, until at least 160 h-1 Mpc. We also present a detailed discussion of our dipole profile, linking observed features to the structures and superclusters that produce them. We find that most of the dipole signal at large distances can be attributed to the Shapley supercluster centered at about 150 h-1 Mpc and a handful of very massive individual clusters, some of which are newly discovered and lie well inside the zone of avoidance.