Young star cluster populations in the E-MOSAICS simulations
  We present an analysis of young star clusters (YSCs) that form in the
E-MOSAICS cosmological, hydrodynamical simulations of galaxies and their star
cluster populations. Through comparisons with observed YSC populations, this
work aims to test models for YSC formation and obtain an insight into the
formation processes at work in part of the local galaxy population. We find
that the models used in E-MOSAICS for the cluster formation efficiency and
high-mass truncation of the initial cluster mass function ($M_\mathrm{c,\ast}$)
both quantitatively reproduce the observed values of cluster populations in
nearby galaxies. At higher redshifts ($z \geq 2$, near the peak of globular
cluster formation) we find that, at a constant star formation rate (SFR)
surface density, $M_\mathrm{c,\ast}$ is larger than at $z=0$ by a factor of
four due to the higher gas fractions in the simulated high-redshift galaxies.
Similar processes should be at work in local galaxies, offering a new way to
test the models. We find that cluster age distributions may be sensitive to
variations in the cluster formation rate (but not SFR) with time, which may
significantly affect their use in tests of cluster mass loss. By comparing
simulations with different implementations of cluster formation physics, we
find that (even partially) environmentally-independent cluster formation is
inconsistent with the brightest cluster-SFR and specific
luminosity-$\Sigma_\mathrm{SFR}$ relations, whereas these observables are
reproduced by the fiducial, environmentally-varying model. This shows that
models in which a constant fraction of stars form in clusters are inconsistent
with observations.
