Large fluctuations in the hydrogen-ionizing background and mean free path following the epoch of reionization

TL;DR

This paper develops a self-consistent model of the ionizing background during the epoch of reionization, accounting for fluctuations in mean free path and large-scale density variations, improving agreement with observed Lyman-alpha forest data.

Contribution

It introduces a novel model incorporating mean free path fluctuations and large-scale density effects to better match Lyman-alpha forest observations during reionization.

Findings

Model reproduces large-scale opacity fluctuations in Lyman-alpha forest.

Fluctuations in mean free path are driven by density and ionizing background variations.

Large simulation volumes are necessary to capture rare features.

Abstract

Extremely large opaque troughs in the Lyman-alpha forest have been interpreted as a sign of an extended reionization process below z~6. Such features are impossible to reproduce with simple models of the intergalactic ionizing background that assume a uniform mean free path of ionizing photons. We build a self-consistent model of the ionizing background that includes fluctuations in the mean free path due to the varying strength of the ionizing background and large-scale density field. The dominant effect is the suppression of the ionizing background in large-scale voids due to "self-shielding" by an enhanced number of optically thick absorbers. Our model results in a distribution of 50 Mpc/h Lyman-alpha forest effective optical depths that significantly improves agreement with the observations at z~5.6. Extrapolation to z~5.4 and z~5.8 appears promising, but matching the mean background evolution requires evolution in the absorber population beyond the scope of the present model. We also demonstrate the need for extremely large volumes (>400 Mpc on a side) to accurately determine the incidence of rare large-scale features in the Lyman-alpha forest.