Feedback Regulated Turbulence, Magnetic Fields, and Star Formation Rates
  in Galactic Disks
  We use three-dimensional magnetohydrodynamic (MHD) simulations to investigate
the quasi-equilibrium states of galactic disks regulated by star formation
feedback. We incorporate effects from massive-star feedback via time-varying
heating rates and supernova (SN) explosions. We find that the disks in our
simulations rapidly approach a quasi-steady state that satisfies vertical
dynamical equilibrium. The star formation rate (SFR) surface density
self-adjusts to provide the total momentum flux (pressure) in the vertical
direction that matches the weight of the gas. We quantify feedback efficiency
by measuring feedback yields, \eta_c\equiv P_c/\Sigma_SFR (in suitable units),
for each pressure component. The turbulent and thermal feedback yields are the
same for HD and MHD simulations, \eta_th~1 and \eta_ turb~4, consistent with
the theoretical expectations. In MHD simulations, turbulent magnetic fields are
rapidly generated by turbulence, and saturate at a level corresponding to
\eta_mag,t~1. The presence of magnetic fields enhances the total feedback yield
and therefore reduces the SFR, since the same vertical support can be supplied
at a smaller SFR. We suggest further numerical calibrations and observational
tests in terms of the feedback yields.
