Runaway Stars and the Escape of Ionizing Radiation from High-Redshift
  Galaxies
  Approximately 30% of all massive stars in the Galaxy are runaways with
velocities exceeding 30 km/s. Their high speeds allow them to travel ~0.1-1 kpc
away from their birth place before they explode at the end of their several Myr
lifetimes. At high redshift, when galaxies were much smaller than in the local
universe, runaways could venture far from the dense inner regions of their host
galaxies. From these large radii, and therefore low column densities, much of
their ionizing radiation is able to escape into the intergalactic medium.
Runaways may therefore significantly enhance the overall escape fraction of
ionizing radiation, fesc, from small galaxies at high redshift. We present
simple models of the high-redshift runaway population and its impact on fesc as
a function of halo mass, size, and redshift. We find that the inclusion of
runaways enhances fesc by factors of ~1.1-8, depending on halo mass, galaxy
geometry, and the mechanism of runaway production, implying that runaways may
contribute 50-90% of the total ionizing radiation escaping from high-redshift
galaxies. Runaways may therefore play an important role in reionizing the
universe.
