The angular momentum structure of cosmic ray driven galactic outflows
  triggered by stream accretion
  We investigate the impact of gas accretion in streams on the evolution of
disc galaxies, using magneto-hydrodynamic simulations including advection and
anisotropic diffusion of cosmic rays generated by supernovae as the only source
of feedback. Stream accretion has been suggested as an important galaxy growth
mechanism in cosmological simulations and we vary their orientation and angular
momentum in idealised setups. We find that accretion streams trigger the
formation of galactic rings and enhanced star formation. The star formation
rates and consequently the cosmic ray driven outflow rates are higher for low
angular momentum accretion streams, which also result in more compact, lower
angular momentum discs. The cosmic ray generated outflows show a characteristic
structure. At low outflow velocities (< 50 km/s) the angular momentum
distribution is similar to the disk and the gas is in a fountain flow. Gas at
high outflow velocities (> 200 km/s), penetrating deep into the halo, has close
to zero angular momentum, and originates from the centre of the galaxies. As
the mass loading factors of the cosmic ray driven outflows are of order unity
and higher, we conclude that this process is important for the removal of low
angular momentum gas from evolving disk galaxies and the transport of,
potentially metal enriched, material from galactic centres far into the
galactic haloes.
