Galactic winds driven by isotropic and anisotropic cosmic ray diffusion
  in disk galaxies
  The physics of cosmic rays (CR) is a promising candidate for explaining the
driving of galactic winds and outflows. Recent galaxy formation simulations
have demonstrated the need for active CR transport either in the form of
diffusion or streaming to successfully launch winds in galaxies. However, due
to computational limitations, most previous simulations have modeled CR
transport isotropically. Here, we discuss high resolution simulations of
isolated disk galaxies in a $10^{11}\rm{M_\odot}$ halo with the moving mesh
code {\sc Arepo} that include injection of CRs from supernovae, advective
transport, CR cooling, and CR transport through isotropic or anisotropic
diffusion. We show that either mode of diffusion leads to the formation of
strong bipolar outflows. However, they develop significantly later in the
simulation with anisotropic diffusion compared to the simulation with isotropic
diffusion. Moreover, we find that isotropic diffusion allows most of the CRs to
quickly diffuse out of the disk, while in the simulation with anisotropic
diffusion, most CRs remain in the disk once the magnetic field becomes
dominated by its azimuthal component, which occurs after $\sim 300\,{\rm
Myrs}$. This has important consequences for the gas dynamics in the disk. In
particular, we show that isotropic diffusion strongly suppresses the
amplification of the magnetic field in the disk compared to anisotropic or no
diffusion models. We therefore conclude that reliable simulations which include
CR transport inevitably need to account for anisotropic diffusion.
