# BCG Mass Evolution in Cosmological Hydro-Simulations

## TL;DR

This study uses cosmological hydrodynamical simulations to analyze the stellar mass growth of Brightest Cluster Galaxies, finding results consistent with observations and supporting an inside-out formation scenario.

## Contribution

First detailed analysis of BCG mass evolution in cosmological hydro-simulations, comparing different methods and apertures, and linking assembly history with cluster evolution.

## Key findings

- BCG masses at z=0 match recent observations.
- Mass growth factors from z=1 to z=0 are consistent with observations.
- BCGs assemble half their stellar mass around redshift 1.5.

## Abstract

We analyze the stellar growth of Brightest Cluster Galaxies (BCGs) produced by cosmological zoom-in hydrodynamical simulations of the formation of massive galaxy clusters. The evolution of the stellar mass content is studied considering different apertures, and tracking backwards either the main progenitor of the $z=0$ BCG or that of the cluster hosting the BCG at $z=0$. Both methods lead to similar results up to $z \simeq 1.5$. The simulated BCGs masses at $z=0$ are in agreement with recent observations. In the redshift interval from $z=1$ to $z=0$ we find growth factors 1.3, 1.6 and 3.6 for stellar masses within 30kpc, 50kpc and 10% of $R_{500}$ respectively. The first two factors, and in general the mass evolution in this redshift range, are in agreement with most recent observations. The last larger factor is similar to the growth factor obtained by a semi-analytical model (SAM). Half of the star particles that end up in the inner 50 kpc was typically formed by redshift $\sim$ 3.7, while the assembly of half of the BCGs stellar mass occurs on average at lower redshifts $\sim 1.5$. This assembly redshift correlates with the mass attained by the cluster at high $z \gtrsim 1.3$, due to the broader range of the progenitor clusters at high-$z$. The assembly redshift of BCGs decreases with increasing apertures. Our results are compatible with the {\it inside-out} scenario. Simulated BCGs could lack intense enough star formation (SF) at high redshift, while possibly exhibit an excess of residual SF at low redshift.