The Structure of Reionization in Hierarchical Galaxy Formation Models
  Understanding the epoch of reionization and the properties of the first
galaxies represents an important goal for modern cosmology. The structure of
reionization, and hence the observed power spectrum of redshifted 21cm
fluctuations are 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 make
predictions for the ionised structure during reionization and the 21cm power
spectrum based on detailed models of galaxy formation. We combine the
semi-analytic GALFORM model implemented within the Millennium-II dark matter
simulation, with a semi-numerical scheme to describe the resulting ionization
structure. Using these models we show that the details of SNe and radiative
feedback affect the structure and distribution of ionised regions, and hence
the slope and amplitude of the 21 cm power spectrum. These results indicate
that forthcoming measurements of the 21cm power-spectrum could be used to
uncover details of early galaxy formation. We find that the strength of SNe
feedback is the dominant effect governing the evolution of structure during
reionization. In particular we show SNe feedback to be more important than
radiative feedback, the presence of which we find does not influence either the
total stellar mass or overall ionising photon budget. Thus, if SNe feedback is
effective at suppressing star formation in high redshift galaxies, we find that
photoionization feedback does not lead to self-regulation of the reionization
process as has been thought.
