The cross-power spectrum between 21cm emission and galaxies in
  hierarchical galaxy formation models
  The correlation between 21cm fluctuations and galaxies is sensitive to the
astrophysical properties of the galaxies that drove reionization. Thus,
detailed measurements of the cross-power spectrum and its evolution could
provide a powerful measurement both of the properties of early galaxies and the
process of reionization. In this paper, we study the evolution of the
cross-power spectrum between 21cm emission and galaxies using a model 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. We find that inclusion of different
feedback processes changes the cross-power spectrum shape and amplitude. In
particular, the feature in the cross-power spectrum corresponding to the size
of ionized regions is significantly affected by supernovae feedback. We
calculate predicted observational uncertainties of the cross-correlation
coefficient based on specifications of the Murchison Widefield Array (MWA)
combined with galaxy surveys of varying area and depth. We find that the
cross-power spectrum could be detected over several square degrees of galaxy
survey with galaxy redshift errors less than 0.1.
