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 \sigma _ { z } \lesssim 0.1 .