Galaxy Alignments as a Probe of the Dynamical State of Clusters

Abstract

Abell: We present indications, based on a sample of 303 Abell clusters, for a relation between the dynamical state of clusters and the alignments of galaxy members with their parent cluster major-axis orientation as well as with the large-scale environment within which the clusters are embedded. The statistical results are complemented with a deep, wide-field case study of galaxy alignments in the cluster A521, which is characterized by multiple merging events (Maurogrdato et al.; Ferrari et al.) and whose galaxy members show a strong alignment signal out to ~5 h^-1 Mpc. Our results show that galaxy alignments appear to be stronger the more dynamically young the cluster is, especially when found in high-density environments. This relation complements the recently found ``cluster substructure-alignment connection'' (Plionis & Basilakos) by which dynamically young clusters, found in high-density environments, show stronger cluster-cluster alignments.