The imprint of cosmic ray driven outflow on Lyman-alpha spectra
  Recent magneto-hydrodynamic simulations of the star-forming interstellar
medium (ISM) with parsec scale resolution indicate that relativistic cosmic
rays support the launching of galactic outflows on scales of a few kpc. If
these fundamental constituents of the ISM are injected at the sites of
supernova (SN) explosions, the outflows are smoother, colder, and denser than
the highly structured, hot-phase driven outflows forming, e.g., by thermal SN
energy injection alone. In this Letter we present computations of resonant
Lyman-$\alpha$ (Ly$\alpha$) radiation transfer through snapshots of a suite of
stratified disk simulations from the SILCC project. For a range of thermal,
radiative, and kinetic feedback models only simulations including non-thermal
cosmic rays produce Ly$\alpha$ spectra with enhanced red peaks and strong
absorption at line center -- similar to observed systems. The absence of cosmic
ray feedback leads to spectra incompatible with observations. We attribute this
to the smoother neutral gas distribution of cosmic ray supported outflows
within a few kpc from the disk midplane.
