The stellar mass function and evolution of the density profile of galaxy clusters from the Hydrangea simulations at $0<z<1.5$

TL;DR

This study compares cosmological hydrodynamic simulations with observational data of galaxy clusters from redshift 0 to 1.5, focusing on stellar mass, galaxy distribution, and density profiles to understand cluster evolution.

Contribution

It provides a detailed comparison between Hydrangea simulations and observations, highlighting agreements and discrepancies in galaxy cluster properties across redshifts.

Findings

Simulations agree with observations on stellar mass to halo mass ratio and stellar mass function.

Simulations show higher stellar concentrations than observed at low redshifts.

The concentration of cluster galaxies increases with redshift, opposite to dark matter halo trends.

Abstract

Galaxy clusters are excellent probes to study the effect of environment on galaxy formation and evolution. Along with high-quality observational data, accurate cosmological simulations are required to improve our understanding of galaxy evolution in these systems. In this work, we compare state-of-the-art observational data of massive galaxy clusters ($>10^{14} \textrm{M}_{\odot}$) at different redshifts ($0<z<1.5$) with predictions from the Hydrangea suite of cosmological hydrodynamic simulations of 24 massive galaxy clusters ($>10^{14} \textrm{M}_{\odot}$ at $z=0$). We compare three fundamental observables of galaxy clusters: the total stellar mass to halo mass ratio, the stellar mass function (SMF), and the radial mass density profile of the cluster galaxies. In the first two of these, the simulations agree well with the observations, albeit with a slightly too high abundance of $M_\star \lesssim 10^{10} \textrm{M}_{\odot}$ galaxies at $z \gtrsim 1$. The NFW concentrations of cluster galaxies increase with redshift, in contrast to the decreasing dark matter halo concentrations. This previously observed behaviour is therefore due to a qualitatively different assembly of the smooth DM halo compared to the satellite population. Quantitatively, we however find a discrepancy in that the simulations predict higher stellar concentrations than observed at lower redshifts ($z<0.3$), by a factor of $\approx$2. This may be due to selection bias in the simulations, or stem from shortcomings in the build-up and stripping of their inner satellite halo.