Velocity dispersion of the brightest cluster galaxies in cosmological simulations

TL;DR

This study uses hydrodynamical simulations to analyze the velocity dispersion of Brightest Cluster Galaxies and their surrounding light, finding good agreement with observations and confirming the robustness of velocity dispersion profiles as indicators of cluster mass.

Contribution

The paper demonstrates that cosmological simulations accurately reproduce the velocity dispersion profiles and scaling relations of BCGs, supporting their use in understanding galaxy cluster dynamics.

Findings

Simulations match observed BCG and cluster velocity dispersion relations.

Velocity dispersion profiles are consistent with observational data.

The slope of the BCG velocity dispersion profile correlates with cluster mass.

Abstract

Using the DIANOGA hydrodynamical zoom-in simulation set of galaxy clusters, we analyze the dynamics traced by stars belonging to the Brightest Cluster Galaxies (BCGs) and their surrounding diffuse component, forming the intracluster light (ICL), and compare it to the dynamics traced by dark matter and galaxies identified in the simulations. We compute scaling relations between the BCG and cluster velocity dispersions and their corresponding masses (i.e. $M_\mathrm{BCG}^{\star}$- $\sigma_\mathrm{BCG}^{\star}$, $M_{200}$- $\sigma_{200}$, $M_\mathrm{BCG}^{\star}$- $M_{200}$, $\sigma_\mathrm{BCG}^{\star}$- $\sigma_{200}$), we find in general a good agreement with observational results. Our simulations also predict $\sigma_\mathrm{BCG}^{\star}$- $\sigma_{200}$ relation to not change significantly up to redshift $z=1$, in line with a relatively slow accretion of the BCG stellar mass at late times. We analyze the main features of the velocity dispersion profiles, as traced by stars, dark matter, and galaxies. As a result, we discuss that observed stellar velocity dispersion profiles in the inner cluster regions are in excellent agreement with simulations. We also report that the slopes of the BCG velocity dispersion profile from simulations agree with what is measured in observations, confirming the existence of a robust correlation between the stellar velocity dispersion slope and the cluster velocity dispersion (thus, cluster mass) when the former is computed within $0.1 R_{500}$. Our results demonstrate that simulations can correctly describe the dynamics of BCGs and their surrounding stellar envelope, as determined by the past star-formation and assembly histories of the most massive galaxies of the Universe.