The spatial distribution of satellites in galaxy clusters

TL;DR

This study analyzes the spatial distribution of satellite galaxies in galaxy clusters, revealing that they are more anisotropic than in smaller galaxies, with alignments related to the host halo's shape and evolution over redshift.

Contribution

It extends previous studies of satellite distributions to galaxy clusters using SDSS and Millennium simulation data, highlighting anisotropy and alignment patterns.

Findings

Satellites in clusters are more anisotropic than in Milky Way-like galaxies.

The plane of satellites aligns with the host halo's minor axis.

Anisotropy increases with redshift at fixed cluster mass.

Abstract

The planar distributions of satellite galaxies around the Milky Way and Andromeda have been extensively studied as potential challenges to the standard cosmological model. Using the Sloan Digital Sky Survey and the Millennium simulation we extend such studies to the satellite galaxies of massive galaxy clusters. We find that both observations and simulations of galaxy clusters show an excess of anisotropic satellite distributions. On average, satellites in clusters have a higher degree of anisotropy than their counterparts in Milky-Way-mass hosts once we account for the difference in their radial distributions. The normal vector of the plane of satellites is strongly aligned with the host halo's minor axis, while the alignment with the large-scale structure is weak. At fixed cluster mass, the degree of anisotropy is higher at higher redshift. This reflects the highly anisotropic nature of satellites accretion points, a feature that is partly erased by the subsequent orbital evolution of the satellites. We also find that satellite galaxies are mostly accreted singly so group accretion is not the explanation for the high flattening of the planes of satellites.