Heating of the Intergalactic Medium by Hydrogen Reionization
  During reionization, the intergalactic medium is heated impulsively by
supersonic ionization fronts (I-fronts). The peak gas temperatures behind the
I-fronts, $T_\mathrm{reion}$, are a key uncertainty in models of the thermal
history after reionization. Here we use high-resolution radiative transfer
simulations to study the parameter space of $T_\mathrm{reion}$. We show that
$T_\mathrm{reion}$ is only mildly sensitive to the spectrum of incident
radiation over most of the parameter space, with temperatures set primarily by
I-front speeds. We also explore what current models of reionization predict for
$T_\mathrm{reion}$ by measuring I-front speeds in cosmological radiative
transfer simulations. We find that the post-I-front temperatures evolve toward
hotter values as reionization progresses. Temperatures of $T_\mathrm{reion} =
17,000-22,000$ K are typical during the first half of reionization, but
$T_\mathrm{reion} = 25,000 - 30,000$ K may be achieved near the end of this
process if I-front speeds reach $\sim10^4$ km/s as found in our simulations.
Shorter reionization epochs lead to hotter $T_\mathrm{reion}$. We discuss
implications for $z>5$ Ly$\alpha$ forest observations, which potentially
include sight lines through hot, recently reionized patches of the Universe.
Interpolation tables from our parameter space study are made publicly
available, along with a simple fit for the dependence of $T_\mathrm{reion}$ on
the I-front speed.
