ALIGNMENT EFFECTS OF CLUSTERS OF GALAXIES

We present the measurement of 204 position angles of the brightest cluster galaxies in a sample of southern clusters. We analyze cluster-cluster alignment effects in this sample and extend it with previous sample of Abell clusters in the northern hemisphere. Binggeli's (1982) test is used with distances derived from the log cz-m10 relationship, giving an alignment signal consistent with redshift derived distances. Our results suggest a weak but statistically significant signal of alignment of the brightest galaxy in a cluster with the projected vector toward the nearest-neighbor cluster. The anisotropy detected amounts approximately to a 30% excess of brightest cluster galaxies pointing to the nearest cluster of galaxies. The mean acute angle between the galaxy position angle and the direction toward the nearest neighbor is 〈φ〉 ≃30° ± 2°, or less. The scale of the detected anisotropy is D ≃ 15 Mpc/h. The statistical results are controlled by means of Monte Carlo simulations and several points concerning the cluster-cluster alignment effects are discussed.