We use a fully self-consistent cosmological simulation including dark matter dynamics , multispecies hydrodynamics , chemical ionization , flux limited diffusion radiation transport , and a parameterized model of star formation and feedback ( thermal and radiative ) to investigate the epoch of hydrogen reionization in detail .
Our numerical method is scalable with respect to the number of radiation sources , size of the mesh , and the number of computer processors employed , and is described in Paper I of this series .
In this the first of several application papers , we investigate the mechanics of reionization from stellar sources forming in high-z galaxies , the utility of various formulations for the gas clumping factor on accurately estimating the effective recombination time in the IGM , and the photon budget required to achieve reionization .
We also test the accuracy of the static and time-dependent models of Madau et al .
as predictors of reionization completion/maintenance .

We simulate a WMAP7 \Lambda CDM cosmological model in a 20 Mpc comoving cube , resolved with 800 ^ { 3 } uniform fluid cells and dark matter particles .
By tuning our star formation recipe to approximately match the observed high redshift star formation rate density and galaxy luminosity function , we have created a fully coupled radiation hydrodynamical realization of hydrogen reionization which begins to ionize at z \approx 10 and completes at z \approx 5.8 without further tuning .
The complicated events during reionization that lead to this number can be generally described as inside-out , but in reality the narrative depends on the level of ionization of the gas one attributes to as ionized .
We find that roughly 2 ionizing photons per H atom are required to convert the neutral IGM to a highly ionized state , which supports the ‘ ‘ photon starved ’ ’ reionization scenario discussed by Bolton & Haehnelt .
We find that the formula for the ionizing photon production rate \dot { \mathcal { N } } _ { ion } ( z ) needed to maintain the IGM in an ionized state derived by Madau et al .
should not be used to predict the epoch of reionization completion because it ignores history-dependent terms in the global ionization balance which are not ignorable .
We find that the time-dependent model for the ionized volume fraction Q _ { H { \footnotesize II } ~ { } } is more predictive , but overestimates the redshift of reionization completion z _ { reion } by \Delta z \approx 1 .
We propose a revised formulation of the time-dependent model which agrees with our simulation to high accuracy .
Finally , we use our simulation data to estimate a globally averaged ionizing escape fraction due to circumgalactic gas resolved on our mesh \bar { f } _ { esc } ( CGM ) \approx 0.7 .