Variation in the escape fraction of ionising photons from galaxies and
  the redshifted 21-cm power spectrum during reionization
  The observed power spectrum of redshifted 21cm fluctuations is known to be
sensitive to the astrophysical properties of the galaxies that drove
reionization. Thus, detailed measurements of the 21cm power spectrum and its
evolution could lead to measurements of the properties of early galaxies that
are otherwise inaccessible. In this paper, we study the effect of mass and
redshift dependent escape fractions of ionizing radiation on the ability of
forthcoming experiments to constrain galaxy formation via the redshifted 21cm
power spectrum. We use a model for reionization which combines the hierarchical
galaxy formation model GALFORM implemented within the Millennium-II dark matter
simulation, with a semi-numerical scheme to describe the resulting ionization
structure. Using this model we show that the structure and distribution of
ionised regions at fixed neutral fraction, and hence the slope and amplitude of
the 21 cm power spectrum, is dependent on the variation of ionising photon
escape fraction with galaxy mass and redshift. However, we find that the
influence of the unknown escape fraction and its evolution is smaller than the
dominant astrophysical effect provided by SNe feedback strength in high
redshift galaxies. The unknown escape fraction of ionizing radiation from
galaxies is therefore unlikely to prevent measurement of the properties of high
redshift star formation using observations of the 21cm power spectrum.
