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