Cosmic-Ray Transport in Varying Galactic Environments
  We study the propagation of mildly-relativistic cosmic rays (CRs) in
multiphase interstellar medium environments with conditions typical of nearby
disk galaxies. We employ the techniques developed in Armillotta+21 to
post-process three high-resolution TIGRESS magnetohydrodynamic simulations
modeling local patches of star-forming galactic disks. Together, the three
simulations cover a wide range of gas surface density, gravitational potential,
and star formation rate (SFR). Our prescription for CR propagation includes the
effects of advection by the background gas, streaming along the magnetic field
at the local ion Alfv\'en speed, and diffusion relative to the Alfv\'en waves,
with the diffusion coefficient set by the balance between streaming-driven
Alfv\'en wave excitation and damping mediated by local gas properties. We find
that the combined transport processes are more effective in environments with
higher SFR. These environments are characterized by higher-velocity hot
outflows (created by clustered supernovae) that rapidly advect CRs away from
the galactic plane. As a consequence, the ratio of midplane CR pressure to
midplane gas pressures decreases with increasing SFR. We also use the
post-processed simulations to make predictions regarding potential dynamical
impacts of CRs. The relatively flat CR pressure profiles near the midplane
argue that they would not provide significant support against gravity for most
of the ISM mass. However, the CR pressure gradients are larger than the other
pressure gradients in the extra-planar region (|z|>0.5 kpc), suggesting that
CRs may affect the dynamics of galactic fountains and/or winds. The degree of
this impact is expected to increase in environments with lower SFR.
