Kiloparsec-Scale Simulations of Magnetised Molecular Clouds in Disk
  Galaxies
  We present simulations of the evolution of self-gravitating dense gas on
kiloparsec-size scales in a galactic disk, designed to study dense clump
formation from giant molecular clouds (GMCs). These dense clumps are expected
to be the precursors to star clusters and this process may be the rate limiting
step controling star formation rates in galactic systems as described by the
Kennicutt-Schmidt relation. The evolution of these simulated GMCs and clumps is
determined by self-gravity balanced by turbulent pressure support and the large
scale galactic shear. While the cloud structures and densities significantly
change during their evolution, they remain roughly in virial equilibrium for
time scales exceeding the free-fall time of GMCs, indicating that energy from
the galactic shear continuously cascades down. We implement star formation at a
slow, inefficient rate of 2% per local free-fall time, but this yields global
star formation rates that are more than ~two orders of magnitude larger than
the observed Kennicutt-Schmidt relation due to the over-production of dense
clump gas. To explain this discrepancy, we anticipate magnetic fields to
provide additional support. Low-resolution simulations indeed show that the
magnetic field reduces the star formation rate.
