Comparison Of Reionization Models: Radiative Transfer Simulations And
  Approximate, Semi-Numeric Models
  We compare the predictions of four different algorithms for the distribution
of ionized gas during the Epoch of Reionization. These algorithms are all used
to run a 100 Mpc/h simulation of reionization with the same initial conditions.
Two of the algorithms are state-of-the-art ray-tracing radiative transfer codes
that use disparate methods to calculate the ionization history. The other two
algorithms are fast but more approximate schemes based on iterative application
of a smoothing filter to the underlying source and density fields. We compare
these algorithms' resulting ionization and 21 cm fields using several different
statistical measures. The two radiative transfer schemes are in excellent
agreement with each other (with the cross-correlation coefficient of the
ionization fields >0.8 for k < 10 h/Mpc and in good agreement with the analytic
schemes (>0.6 for k < 1 h/Mpc). When used to predict the 21cm power spectrum at
different times during reionization, all ionization algorithms agree with one
another at the 10s of percent level. This agreement suggests that the different
approximations involved in the ray tracing algorithms are sensible and that
semi-numerical schemes provide a numerically-inexpensive, yet fairly accurate,
description of the reionization process.
