Shapes and Probabilities of Galaxy Clusters

TL;DR

This paper presents a theoretical framework for estimating the likelihood of various galaxy cluster shapes based on their quasi-equilibrium state, highlighting the probability of different subcluster arrangements.

Contribution

It introduces a new theory linking galaxy cluster shapes to their virialized subcluster configurations, enabling probability comparisons of spatial arrangements.

Findings

Clusters with more than 10 subclusters are likely virialized.

Linear arrangements of subclusters are more probable than ring configurations.

The theory constrains possible cluster shapes based on quasi-equilibrium conditions.

Abstract

We develop a general theory for estimating the probability that a galaxy cluster of a given shape exists. The theory is based on the observed result that the distribution of galaxies is very close to quasi-equilibrium, in both its linear and nonlinear regimes. This places constraints on the spatial configuration of a cluster of galaxies in quasi-equilibrium. In particular, we show that that a cluster of galaxies may be described as a collection of nearly virialized subclusters of approximately the same mass. Clusters that contain more than 10 subclusters are very likely to be completely virialized. Using our theory, we develop a method for comparing probabilities of different spatial configurations of subclusters. As an illustrative example, we show that a cluster of galaxies arranged in a line is more likely to occur than a cluster of galaxies arranged in a ring.