Magnetic Fields and Galactic Star Formation Rates
  The regulation of galactic-scale star formation rates (SFRs) is a basic
problem for theories of galaxy formation and evolution: which processes are
responsible for making observed star formation rates so inefficient compared to
maximal rates of gas content divided by dynamical timescale? Here we study the
effect of magnetic fields of different strengths on the evolution of giant
molecular clouds (GMCs) within a kiloparsec patch of a disk galaxy and
resolving scales down to $\simeq0.5\:{\rm{pc}}$. Including an empirically
motivated prescription for star formation from dense gas
($n_{\rm{H}}>10^5\:{\rm{cm}^{-3}}$) at an efficiency of 2\% per local free-fall
time, we derive the amount of suppression of star formation by magnetic fields
compared to the nonmagnetized case. We find GMC fragmentation, dense clump
formation and SFR can be significantly affected by the inclusion of magnetic
fields, especially in our strongest investigated $B$-field case of
$80\:{\rm{\mu}}$G. However, our chosen kpc-scale region, extracted from a
global galaxy simulation, happens to contain a starbursting cloud complex that
is only modestly affected by these magnetic fields and likely requires internal
star formation feedback to regulate its SFR.
