Simulations of disk galaxies with cosmic ray driven galactic winds
  We present results from high-resolution hydrodynamic simulations of isolated
SMC- and Milky Way-sized galaxies that include a model for feedback from
galactic cosmic rays (CRs). We find that CRs are naturally able to drive winds
with mass loading factors of up to ~10 in dwarf systems. The scaling of the
mass loading factor with circular velocity between the two simulated systems is
consistent with \propto v_c^{1-2} required to reproduce the faint end of the
galaxy luminosity function. In addition, simulations with CR feedback reproduce
both the normalization and the slope of the observed trend of wind velocity
with galaxy circular velocity. We find that winds in simulations with CR
feedback exhibit qualitatively different properties compared to SN driven
winds, where most of the acceleration happens violently in situ near star
forming sites. In contrast, the CR-driven winds are accelerated gently by the
large-scale pressure gradient established by CRs diffusing from the
star-forming galaxy disk out into the halo. The CR-driven winds also exhibit
much cooler temperatures and, in the SMC-sized system, warm (T~10^4 K) gas
dominates the outflow. The prevalence of warm gas in such outflows may provide
a clue as to the origin of ubiquitous warm gas in the gaseous halos of galaxies
detected via absorption lines in quasar spectra.
