Stellar feedback strongly alters the amplification and morphology of
  galactic magnetic fields
  Using high-resolution magnetohydrodynamic simulations of idealized,
non-cosmological galaxies, we investigate how cooling, star formation, and
stellar feedback affect galactic magnetic fields. We find that the
amplification histories, saturation values, and morphologies of the magnetic
fields vary considerably depending on the baryonic physics employed, primarily
because of differences in the gas density distribution. In particular,
adiabatic runs and runs with a sub-grid (effective equation of state) stellar
feedback model yield lower saturation values and morphologies that exhibit
greater large-scale order compared with runs that adopt explicit stellar
feedback and runs with cooling and star formation but no feedback. The
discrepancies mostly lie in gas denser than the galactic average, which
requires cooling and explicit fragmentation to capture. Independent of the
baryonic physics included, the magnetic field strength scales with gas density
as $B\propto n^{2/3}$, suggesting isotropic flux freezing or equipartition
between the magnetic and gravitational energies during the field amplification.
We conclude that accurate treatments of cooling, star formation, and stellar
feedback are crucial for obtaining the correct magnetic field strength and
morphology in dense gas, which, in turn, is essential for properly modeling
other physical processes that depend on the magnetic field, such as cosmic ray
feedback.
