The influence of galaxy mergers on the mass dispersion of brightest cluster galaxies

TL;DR

This study uses simulations to show that galaxy mergers can explain the small variation in the brightness of the brightest cluster galaxies across different clusters, supporting the idea of their dynamical evolution.

Contribution

It demonstrates through statistical simulations that merging processes account for the small mass dispersion of brightest cluster galaxies, aligning with observed data.

Findings

Merger processes are more significant in smaller, compact groups.

The small mass dispersion of BCGs is maintained by limited merger events.

Simulations match observed uniformity in BCG brightness across clusters.

Abstract

The absolute magnitude of the brightest galaxy of clusters varies remarkably little and is nearly independent of all other physical properties of the cluster as, e.g., its spatial extension or its richness. The question arises whether the observed small scatter is compatible with the assumption of dynamical evolution of the cluster. This is investigated with the help of statistical analysis of the results of cluster simulation. The underlying interaction process is merging (and also destruction) of smaller galaxies forming the giant galaxy. The cluster itself is supposed to be in virial equilibrium. We find that the evolutionary importance of merger processes grows with decreasing scale. Rich clusters as well as their brightest members evolve merely slowly whereas compact groups as well as their brightest members evolve more rapidly and more violently. We also find that the number of merger processes leading to the growth of the brightest cluster galaxy (BCG) is small enough to keep the BCG mass dispersion below the measured value. Our simulations substantiate that just the combination of the initial distribution function and the following merging to form the BCG can explain the remarkably small variance of mean BCG masses between clusters of different size and different number of galaxies.