Coevolution of Brightest Cluster Galaxies and Their Host Clusters in IllustrisTNG

Abstract

We use IllustrisTNG simulations to explore the dynamic scaling relation between massive clusters and their-central-brightest cluster galaxies (BCGs). The IllustrisTNG-300 simulation we use includes 280 massive clusters from the z = 0 snapshot with M (200) > 10(14) M (circle dot), enabling a robust statistical analysis. We derive the line-of-sight velocity dispersion of the stellar particles of the BCGs (sigma (*,BCG)), analogous to the observed BCG stellar velocity dispersion. We also compute the subhalo velocity dispersion to measure the cluster velocity dispersion (sigma (cl)). Both sigma (*,BCG) and sigma (cl) are proportional to the cluster halo mass, but the slopes differ slightly. Thus, like the observed relation, sigma (*,BCG)/sigma (cl) declines as a function of sigma (cl), but the scatter is large. We explore the redshift evolution of the sigma (*,BCG) - sigma (cl) scaling relation for z less than or similar to 1 in a way that can be compared directly with observations. The scaling relation has a similar slope at high redshift, but the scatter increases because of the large scatter in sigma (*,BCG). The simulations imply that high-redshift BCGs are dynamically more complex than their low-redshift counterparts.