Non-universal star formation efficiency in turbulent ISM
  We present a study of a star formation prescription in which star formation
efficiency depends on local gas density and turbulent velocity dispersion, as
suggested by direct simulations of SF in turbulent giant molecular clouds
(GMCs). We test the model using a simulation of an isolated Milky Way-sized
galaxy with a self-consistent treatment of turbulence on unresolved scales. We
show that this prescription predicts a wide variation of local star formation
efficiency per free-fall time, $\epsilon_{\rm ff} \sim 0.1 - 10\%$, and gas
depletion time, $t_{\rm dep} \sim 0.1 - 10$ Gyr. In addition, it predicts an
effective density threshold for star formation due to suppression of
$\epsilon_{\rm ff}$ in warm diffuse gas stabilized by thermal pressure. We show
that the model predicts star formation rates in agreement with observations
from the scales of individual star-forming regions to the kiloparsec scales.
This agreement is non-trivial, as the model was not tuned in any way and the
predicted star formation rates on all scales are determined by the distribution
of the GMC-scale densities and turbulent velocities $\sigma$ in the cold gas
within the galaxy, which is shaped by galactic dynamics. The broad agreement of
the star formation prescription calibrated in the GMC-scale simulations with
observations, both gives credence to such simulations and promises to put star
formation modeling in galaxy formation simulations on a much firmer theoretical
footing.
