IllustrisTNG Snapshots for 10 Gyr of Dynamical Evolution of Brightest Cluster Galaxies and Their Host Clusters

TL;DR

This study uses the IllustrisTNG-300 simulation to analyze the evolution of velocity dispersions in massive galaxy clusters and their brightest galaxies over 10 billion years, revealing growth patterns and merger effects.

Contribution

It provides new insights into the dynamical evolution of clusters and BCGs from redshift 2 to 0, highlighting the growth rates and interaction effects with neighboring galaxies.

Findings

Both cluster and BCG velocity dispersions increase over time.

BCG velocity dispersion grows more slowly than cluster dispersion.

Simulation results generally agree with observations at low redshift.

Abstract

We explore the redshift evolution of the dynamical properties of massive clusters and their brightest cluster galaxies (BCGs) at $z < 2$ based on the IllustrisTNG-300 simulation. We select 270 massive clusters with $M_{200} < 10^{14}~{\rm M}_{\odot}$ at $z = 0$ and trace their progenitors based on merger trees. From 67 redshift snapshots covering $z < 2$, we compute the 3D subhalo velocity dispersion as a cluster velocity dispersion ($\sigma_{\rm cl}$). We also calculate the 3D stellar velocity dispersion of the BCGs ($\sigma_{\rm *,~BCG}$). Both $\sigma_{\rm cl}$ and $\sigma_{\rm *,~BCG}$ increase as universe ages. The BCG velocity dispersion grows more slowly than the cluster velocity dispersion. Furthermore, the redshift evolution of the BCG velocity dispersion shows dramatic changes at some redshifts resulting from dynamical interaction with neighboring galaxies (major mergers). We show that $\sigma_{\rm *,~BCG}$ is comparable with $\sigma_{\rm cl}$ at $z > 1$, offering an interesting observational test. The simulated redshift evolution of $\sigma_{\rm cl}$ and $\sigma_{\rm *,~BCG}$ generally agrees with an observed cluster sample for $z < 0.3$, but with large scatter. Future large spectroscopic surveys reaching to high redshift will test the implications of the simulations for the mass evolution of both clusters and their BCGs.