Simulated histories of reionization with merger tree of HII regions

TL;DR

This paper introduces a new method to analyze reionization by tracking the merger histories of HII regions in simulations, providing insights into the evolution and geometry of reionization under different source models.

Contribution

It presents a novel technique to study reionization through merger trees of HII regions, enabling detailed analysis of their evolution and the effects of different source models.

Findings

Different source models lead to distinct reionization geometries.

The methodology effectively tracks the evolution of individual HII regions.

It can quantify the impact of star formation assumptions on reionization history.

Abstract

We describe a new methodology to analyze the reionization process in numerical simulations: The evo- lution of the reionization is investigated by focusing on the merger histories of individual HII regions. From the merger tree of ionized patches, one can track the individual evolution of the regions such as e.g. their size, or investigate the properties of the percolation process by looking at the formation rate, the frequency of mergers and the number of individual HII regions involved in the mergers. By applying this technique to cosmological simulations with radiative transfer, we show how this methodology is a good candidate to quantify the impact of the star formation adopted on the history of the reionization. As an application we show how different models of sources result in different evolutions and geometry of the reionization even though they produce e.g. similar ionized fraction or optical depth.