Einstein CLUSTER ALIGNMENTS REVISITED

摘要

We examine whether the major axes of rich galaxy clusters tend to point toward their nearest neigh- boring cluster. We have used the data of Ulmer, McMillan, and Kowalski, who used position angles based on X-ray morphology. We also study a subset of this sample with updated positions and distances from the MX Northern Abell Cluster Survey [for rich clusters with well-known redshifts. A Kolmogorov-Smirnov (K-S) test shows no significant signal for nonrandom angles on any scale S l00 h-- l Mpc. However, refining the null hypothesis with the Wilcoxon rank-sum test, we found a high con- fidence signal for alignment. Confidence levels increase to a high of 99.997%, since only near neighbors that are very close are considered. We conclude that there is a strong alignment signal in the data, con- sistent with gravitational instability acting on Gaussian perturbations.