The escape of ionising radiation from high-redshift dwarf galaxies
  The UV escape fraction from high-redshift galaxies plays a key role in models
of cosmic reionisation. Because it is currently not possible to deduce the
escape fractions during the epoch of reionisation from observations, we have to
rely on numerical simulations. Our aim is to better constrain the escape
fraction from high-redshift dwarf galaxies, as these are the most likely
sources responsible for reionising the Universe. We employ a N-body/SPH method
that includes realistic prescriptions for the physical processes that are
important for the evolution of dwarf galaxies. These models are post-processed
with radiative transfer to determine the escape fraction of ionising radiation.
We perform a parameter study to assess the influence of the spin parameter, gas
fraction and formation redshift of the galaxy and study the importance of
numerical parameters as resolution, source distribution and local gas clearing.
We find that the UV escape fraction from high-redshift dwarf galaxies that have
formed a rotationally supported disc lie between 1e-5 and 0.1. The mass and
angular momentum of the galaxy are the most important parameters that determine
the escape fraction. We compare our results to previous work and discuss the
uncertainties of our models. The low escape fraction we find for high-redshift
dwarf galaxies is balanced by their high stellar content, resulting in an
efficiency parameter for stars that is only marginally lower than the values
found by semi-analytic models of reionisation. We therefore conclude that dwarf
galaxies play an important role in cosmic reionisation also after the initial
starburst phase, when the gas has settled into a disc.
