Efficient early stellar feedback can suppress galactic outflows by
  reducing supernova clustering
  We present a novel set of stellar feedback models, implemented in the
moving-mesh code Arepo, designed for galaxy formation simulations with
near-parsec (or better) resolution. These include explicit sampling of stars
from the IMF, allowing feedback to be linked to individual massive stars, an
improved method for the modelling of H II regions, photoelectric heating from a
spatially varying FUV field and supernova feedback. We perform a suite of 32
simulations of isolated $M_\mathrm{vir} = 10^{10}\,\mathrm{M_\odot}$ galaxies
with a baryonic mass resolution of $20\,\mathrm{M_\odot}$ in order to study the
non-linear coupling of the different feedback channels. We find that
photoionization and supernova feedback are both independently capable of
regulating star formation to the same level, while photoelectric heating is
inefficient. Photoionization produces a considerably smoother star formation
history than supernovae. When all feedback channels are combined, the
additional suppression of star formation rates is minor. However, outflow rates
are substantially reduced relative to the supernova only simulations. We show
that this is directly caused by a suppression of supernova clustering by the
photoionization feedback, disrupting star forming clouds prior to the first
supernovae. We demonstrate that our results are robust to variations of our
star formation prescription, feedback models and the gas fraction of the disk.
Our results also imply that the burstiness of star formation and the mass
loading of outflows may be overestimated if the adopted star particle mass is
considerably larger than the mass of individual stars because this imposes a
minimum cluster size.
