Effects of the sources of reionization on 21-cm redshift-space distortions

TL;DR

This paper investigates how the anisotropy in the 21-cm signal caused by redshift-space distortions during reionization can inform us about the reionization history, finding that the quadrupole moment is a robust, model-independent probe.

Contribution

It demonstrates that the quadrupole moment of the 21-cm power spectrum is a predictable and effective tool for constraining reionization history across different source models.

Findings

Quadrupole moment evolution is predictable with neutral fraction.

Redshift-space distortions are not highly sensitive to reionization sources.

First-generation instruments can partially measure the reionization history, SKA can do so accurately.

Abstract

The observed 21-cm signal from the epoch of reionization will be distorted along the line-of-sight by the peculiar velocities of matter particles. These redshift-space distortions will affect the contrast in the signal and will also make it anisotropic. This anisotropy contains information about the cross-correlation between the matter density field and the neutral hydrogen field, and could thus potentially be used to extract information about the sources of reionization. In this paper, we study a collection of simulated reionization scenarios assuming different models for the sources of reionization. We show that the 21-cm anisotropy is best measured by the quadrupole moment of the power spectrum. We find that, unless the properties of the reionization sources are extreme in some way, the quadrupole moment evolves very predictably as a function of global neutral fraction. This predictability implies that redshift-space distortions are not a very sensitive tool for distinguishing between reionization sources. However, the quadrupole moment can be used as a model-independent probe for constraining the reionization history. We show that such measurements can be done to some extent by first-generation instruments such as LOFAR, while the SKA should be able to measure the reionization history using the quadrupole moment of the power spectrum to great accuracy.