  The ionizing ultraviolet background (UVB) during reionization can suppress
the gas content of low-mass galaxies, even those capable of efficient atomic
cooling, and thus lead to an extended reionization epoch. In this work, we
explore the importance of negative UV radiative feedback on Tvir > 10^4 K halos
during the middle and late stages of reionization. We do not try to
self-consistently model reionization; instead, we explore a large parameter
space in an attempt to draw general, robust conclusions. We do this using a
tiered approach. Using 1-D hydrodynamical simulations, we model the collapse of
gas onto halos of various masses under UVBs of various intensities. We then
generate realistic, parametrized maps of the inhomogeneous UVB, using
large-scale semi-numeric simulations. By combining these results, we find that
under all reasonably conservative scenarios, UV feedback on atomically-cooled
halos is not strong enough to notably delay the bulk of reionization. Such a
delay is only likely if ionizing efficiencies of z > 10 sources are much higher
(~ two orders of magnitude) than z ~ 6 data seem to imply. We also find that
feedback is very strongly dependent on halo mass. Our results suggest that the
natural time-scale for the bulk of reionization is the growth of the global
collapsed fraction contained in Tvir > 10^4 K halos. Finally, our results
underscore the importance of taking into account extended dynamical ranges when
modeling reionization.
