Comparison of reionization models: radiative transfer simulations and approximate, seminumeric models

Abstract

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(-1) 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 applications of a smoothing filter on 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 judging by the power spectra of both the ionization fields and the 21-cm emission fields ( agreeing to better than 10 per cent) and are in good agreement with the analytic schemes ( better than 50 per cent) over the range of ionized fractions and wavevectors we compare ( 0.2 < <(x)over bar>(i) < 0.7; 0.1 < k < 10 h Mpc(-1)).This agreement suggests that the different approximations involved in the ray-tracing algorithms are sensible and that seminumerical schemes provide a numerically inexpensive, yet fairly accurate, description of the reionization process.