Alignment of Galaxies and Clusters

TL;DR

This study examines the alignment between brightest cluster galaxies and their host clusters using high-resolution X-ray and optical data, revealing a significant alignment but no correlation with cluster morphology or dynamical state.

Contribution

It introduces a method combining high-resolution X-ray and optical data to analyze galaxy-cluster alignments, providing new insights into their relationship.

Findings

Strong alignment between BCGs and cluster X-ray emission.

No correlation between ellipticity of X-ray and optical BCGs.

No dependence of alignment on cluster X-ray morphology.

Abstract

We investigated the influence of environment on cluster galaxies by examining the alignment of the brightest cluster galaxy (BCG) position angle with respect to the host cluster X-ray position angle. The cluster position angles were measured using high spatial resolution X-ray data taken from the Chandra ACIS archive, that significantly improved the determination of the cluster shape compared to the conventional method of using optical images. Meanwhile, those of the BCGs were measured using homogeneous dataset composed of high spatial resolution optical images taken with Suprime-Cam mounted on Subaru 8m telescope. We found a strong indication of an alignment between the cluster X-ray emission and optical light from BCGs, while we see no clear direct correlation between the degree of ellipticity of X-ray and optical BCG morphologies, despite the apparent alignment of two elliptical structures. We have also investigated possible dependence of the position angle alignment on the X-ray morphology of the clusters, and no clear trends are found. The fact that no trends are evident regarding frequency or degree of the alignment with respect to X-ray morphology may be consistent with an interpretation as a lack of dependence on the dynamical status of clusters.