The Orientation of Galaxies in Galaxy Clusters

TL;DR

This study analyzes galaxy orientations in 247 rich Abell clusters, revealing that galaxy alignment anisotropy correlates with cluster richness and environmental factors, with weak links to cluster morphology.

Contribution

It provides the first comprehensive statistical analysis linking galaxy orientation anisotropy to cluster richness and morphology in a large sample.

Findings

Galaxy orientation anisotropy increases with cluster richness.

Weak dependence of galaxy alignments on cluster morphological type.

Velocity dispersion decreases with Bautz-Morgan type at nearly 3σ significance.

Abstract

We present an analysis of the spatial orientations of galaxies in the 247 optically selected rich Abell clusters, having in the considered area at least 100 members. We investigated the relation between angles giving information about galaxy angular momenta and the number of members in each structure. The position angles of the galaxy major axes, as well as two angles describing the spatial orientation of galaxy plane were tested for isotropy, by applying three different statistical tests. It is found that the values of statistics increase with the amount of galaxies' members, which is equivalent to the existence of the relation between anisotropy and number of galaxies in cluster. The search for connection between the galaxies alignments and Bautz - Morgan morphological types of examined clusters gave weak dependence. The statistically marginal relation between velocity dispersion and cluster richness was observed. In addition, it was found that the velocity dispersion decreases with Bautz - Morgan type at almost 3$\sigma$ level. These results shows the dependence of alignments with respect to clusters' richness, which can be regarded as environmental effect.