Global simulations of galactic winds including cosmic ray streaming
  Galactic outflows play an important role in galactic evolution. Despite their
importance, a detailed understanding of the physical mechanisms responsible for
the driving of these winds is lacking. In an effort to gain more insight into
the nature of these flows, we perform global three-dimensional
magneto-hydrodynamical simulations of an isolated Milky Way-size starburst
galaxy. We focus on the dynamical role of cosmic rays injected by supernovae,
and specifically on the impact of the streaming and anisotropic diffusion of
cosmic rays along the magnetic fields. We find that these microphysical effects
can have a significant effect on the wind launching and mass loading factors
depending on the details of the plasma physics. Due to the cosmic ray streaming
instability, cosmic rays propagating in the interstellar medium scatter on
self-excited Alfven waves and couple to the gas. When the wave growth due to
the streaming instability is inhibited by some damping process, such as the
turbulent damping, the cosmic ray coupling to the gas is weaker and their
effective propagation speed faster than the Alfven speed. Alternatively, cosmic
rays could scatter from "extrinsic turbulence" that is driven by another
mechanism. We demonstrate that the presence of moderately super-Alfvenic cosmic
ray streaming enhances the efficiency of galactic wind driving. Cosmic rays
stream away from denser regions near the galactic disk along partially ordered
magnetic fields and, in the process, accelerate more tenuous gas away from the
galaxy. For cosmic ray acceleration efficiencies broadly consistent with the
observational constraints, cosmic rays reduce the galactic star formation rates
and significantly aid in launching galactic winds.
