Reionization in the Warm Dark Matter Model

TL;DR

This paper investigates how warm dark matter influences the timing of cosmic reionization, revealing that despite delayed start, reionization may complete earlier than in cold dark matter models due to reduced recombination in minihalos.

Contribution

It introduces an analytical bubble model to analyze reionization in WDM, showing potential for earlier completion despite delayed onset.

Findings

Reionization initiation is delayed in WDM models.

Reionization completion can occur earlier in WDM than CDM.

Limits on WDM particle mass are derived from reionization timing.

Abstract

Compared with the cold dark matter (CDM) model, in the warm dark matter (WDM) model formation of small scale structure is suppressed. It is often thought that this would delay the reionization of the intergalactic medium (IGM), as the star formation rate during the epoch of reionization (EOR) would be lowered. However, during the later stage of the EOR, a large portion of the ionizing photons are consumed by recombination inside the minihalos, where the gas has higher density and recombination rates than the gas in the IGM. The suppression of small scale structure would therefore reduce the recombination rate, and could potentially shorten the reionization process. This effect is investigated here by using the analytical "bubble model" of reionization. We find that in some cases, though the initiation of the EOR is delayed in the WDM model, its completion could be even earlier than the CDM case, but the effect is generally small. We obtain limits on the WDM particles mass for different reionization redshifts.