The properties, origin and evolution of stellar clusters in galaxy
  simulations and observations
  We investigate the properties and evolution of star particles in two
simulations of isolated spiral galaxies, and two galaxies from cosmological
simulations. Unlike previous numerical work, where typically each star particle
represents one `cluster', for the isolated galaxies we are able to model
features we term `clusters' with groups of particles. We compute the spatial
distribution of stars with different ages, and cluster mass distributions,
comparing our findings with observations including the recent LEGUS survey. We
find that spiral structure tends to be present in older (100s Myrs) stars and
clusters in the simulations compared to the observations. This likely reflects
differences in the numbers of stars or clusters, the strength of spiral arms,
and whether the clusters are allowed to evolve. Where we model clusters with
multiple particles, we are able to study their evolution. The evolution of
simulated clusters tends to follow that of their natal gas clouds. Massive,
dense, long-lived clouds host massive clusters, whilst short-lived clouds host
smaller clusters which readily disperse. Most clusters appear to disperse
fairly quickly, in basic agreement with observational findings. We note that
embedded clusters may be less inclined to disperse in simulations in a galactic
environment with continuous accretion of gas onto the clouds than isolated
clouds and correspondingly, massive young clusters which are no longer
associated with gas tend not to occur in the simulations. Caveats of our models
include that the cluster densities are lower than realistic clusters, and the
simplistic implementation of stellar feedback.
