Implementing Dust Shielding as a Criteria for Star Formation
  Star formation is observed to be strongly correlated to dense regions of
molecular gas. Although the exact nature of the link between star formation and
molecular hydrogen is still unclear, some have suggested that shielding of
dense gas by dust grains is the key factor enabling the presence of both. We
present a sub-grid model for use in galaxy formation simulations in which star
formation is linked explicitly to local dust shielding. We developed and tested
our shielding and star formation models using smoothed particle hydrodynamic
simulations of solar and sub-solar metallicity isolated Milky Way-mass disk
galaxies. We compared our dust shielding-based star formation model to two
other star formation recipes that used gas temperature and H$_2$ fraction as
star formation criteria. We further followed the evolution of a dwarf galaxy
within a cosmological context using both the shielding and H$_2$-based star
formation models. We find that the shielding-based model allows for star
formation at higher temperatures and lower densities than a model in which star
formation is tied directly to H$_2$ abundance, as requiring H$_2$ formation
leads the gas to undergo additional gravitational collapse before star
formation. However, the resulting galaxies are very similar for both the
shielding and H$_2$-based star formation models, and both models reproduce the
resolved Kennicutt-Schmidt law. Therefore, both star formation models appear
viable in the context of galaxy formation simulations.
