  We present results of combined N-body and three-dimensional reionization
calculations to determine the relationship between reionization history and
local environment in a volume 1 Gpc/h across and a resolution of about 1 Mpc.
We resolve the formation of about 2x10^6 halos of mass greater than ~10^12 Msun
at z=0, allowing us to determine the relationship between halo mass and
reionization epoch for galaxies and clusters. For our fiducial reionization
model, in which reionization begins at z~15 and ends by z~6, we find a strong
bias for cluster-size halos to be in the regions which reionized first, at
redshifts 10<z<15. Consequently, material in clusters was reionized within
relatively small regions, on the order of a few Mpc, implying that all clusters
in our calculation were reionized by their own progenitors. Milky Way mass
halos were on average reionized later and by larger regions, with a
distribution similar to the global one, indicating that low mass halos are
relatively uncorrelated with reionization when only their mass is taken as a
prior. On average, we find that most halos with mass less than 10^13 Msun were
reionized internally, while almost all halos with masses greater than 10^14
Msun were reionized by their own progenitors. We briefly discuss the
implications of this work in light of the "missing satellites" problem and how
this new approach may be extended further.
