Comparison Of Reionization Models: Radiative Transfer Simulations And Approximate, Semi-Numeric Models

TL;DR

This study compares four algorithms for modeling the Epoch of Reionization, showing that approximate semi-numerical schemes closely match more complex radiative transfer models in predicting ionization and 21cm signals.

Contribution

It demonstrates that semi-numerical models can reliably approximate detailed radiative transfer simulations in reionization studies.

Findings

Radiative transfer schemes agree with each other (cross-correlation >0.8).

Semi-numerical schemes match radiative transfer results within 10-20%.

All models produce similar 21cm power spectra during reionization.

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 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.