The Neutral Islands during the Late Epoch of Reionization

TL;DR

This paper introduces an analytical and semi-numerical model for the late-stage neutral islands during reionization, incorporating ionizing backgrounds and absorbers to better understand the epoch's large-scale structure.

Contribution

It develops the first island model for the late epoch of reionization, extending the excursion set theory to include neutral islands and their internal bubbles.

Findings

The islandFAST code effectively models neutral island evolution.

The model self-consistently accounts for ionizing backgrounds and absorbers.

Results improve understanding of late reionization structure.

Abstract

The large-scale structure of the ionization field during the epoch of reionization (EoR) can be modeled by the excursion set theory. While the growth of ionized regions during the early stage are described by the "bubble model", the shrinking process of neutral regions after the percolation of the ionized region calls for an "island model". An excursion set based analytical model and a semi-numerical code (islandFAST) have been developed. The ionizing background and the bubbles inside the islands are also included in the treatment. With two kinds of absorbers of ionizing photons, i.e. the large-scale under-dense neutral islands and the small-scale over-dense clumps, the ionizing background are self-consistently evolved in the model.