The Launching of Cosmic Ray Driven Outflows
  Cosmic rays (CRs) are thought to be an important feedback mechanism in
star-forming galaxies. They can provide an important source of pressure support
and possibly drive outflows. We perform multidimensional CR-magnetohydrodynamic
simulations including transport by streaming and diffusion to investigate wind
launching from an initially hydrostatic atmosphere by CRs. We estimate a
characteristic Eddington limit on the CR flux for which the CR force exceeds
gravity and compare it to simulated systems. Scaling our results to conditions
in star-forming galaxies, we find that CRs are likely to contribute to driving
outflows for a broad range of star formation environments. We quantify the
momentum and energy transfer between CRs and gas, along with the associated
mass outflow rates under different assumptions about the relative importance of
streaming and diffusion for transport. In simulations with streaming, we
observe the growth and saturation of the CR acoustic instability, but the CRs
and gas remain well coupled, with CR momentum transferred efficiently to the
gas even when this instability is present. Higher CR fluxes transferr more
energy to the gas and drive stronger outflows. When streaming is present, most
of the transferred energy takes the form of Alfv\'{e}n wave heating of the gas,
raising its pressure and internal energy, with a lower fractional contribution
to the kinetic energy of the outflow. We also consider runs with radiative
cooling, which modifies gas temperature and pressure profiles but does not seem
to have a large impact on the mass outflow for super-Eddington CR fluxes.
