The alignment between brightest cluster galaxies and host clusters

TL;DR

This study investigates the alignment between brightest cluster galaxies and their host clusters using optical and X-ray data, revealing significant alignment patterns and their potential implications for cluster evolution.

Contribution

It provides new evidence of stronger BCG-cluster alignment in X-ray measurements and explores the co-evolution of BCGs with intra-cluster medium morphology.

Findings

BCG-cluster alignment is confirmed and more significant than previous studies.

BCGs align more strongly with X-ray measured cluster orientations.

Alignment strength correlates with BCG brightness and is unaffected by ellipticity or cluster richness.

Abstract

The alignment between brightest cluster galaxies (BCGs) and host clusters can reveal the mystery of formation and evolution for galaxy clusters. We measure cluster orientations in optical based on the projected distribution of member galaxies and in X-ray by fitting the morphology of intra-cluster medium (ICM). Cluster orientations determined in the two wavelengths are generally consistent. The orientation alignment between BCGs and host clusters is confirmed and more significant than previous works. We find that BCGs are more aligned with cluster orientations measured in X-ray than those from optical data. Clusters with a brighter BCG generally show a stronger alignment. We argue that the detected redshift evolution of the alignment is probably caused by observational bias rather than intrinsic evolution. The alignment is not related to the ellipticity of BCGs, and the richness, ellipticity and dynamical state of host clusters. The strong alignment between BCGs and morphology of ICMs may be the consequence of the co-evolution between the central massive galaxy and host clusters.