On Alignment of Galaxies in Clusters

TL;DR

This study investigates galaxy alignments within clusters, finding that alignment is more common in poor clusters and decreases over time due to galaxy accretion and interactions, shedding light on galaxy evolution.

Contribution

It introduces a method to analyze galaxy alignment based on position angles and distinguishes alignment patterns in isolated, low-density cluster regions.

Findings

Galaxy alignment is more frequent in poor clusters.

Alignment decreases as clusters evolve due to galaxy accretion.

Outer regions of clusters show less disturbed galaxy orientations.

Abstract

We discover alignment of galaxies in clusters by analyzing the distribution of their position angles. We assume that galaxies are aligned, if their number at one 90deg position angle interval is more than twice higher than at another 90deg interval. We selected for study the isolated clusters in order to exclude clusters the distribution of the galaxy orientation in which could possibly be altered by gravitational influence of a nearby cluster. Also, we study the galaxy position angle distribution at the outer regions of clusters with small space density where the variation of the position angles in the result of interactions between galaxies is smaller than at the central dens regions used as a control sample. We found that the alignment of galaxies is more often observed in poor clusters. We conclude that originally galaxies were aligned, but in the result of accretion of field galaxies with arbitrary orientation and mutual interactions of galaxies during the cluster evolution the relative part of aligned galaxies decreases.