Reionization by UV or X-ray sources

TL;DR

This paper uses detailed simulations to study the 21-cm signal during reionization, highlighting the impact of X-ray heating and absorption effects, and proposes diagnostics to understand early cosmic sources.

Contribution

The study introduces comprehensive radiative transfer simulations that incorporate inhomogeneous Wouthuysen-Field effect and X-ray heating, providing new insights into the 21-cm signal during reionization.

Findings

Brightness temperature fluctuations exceed 100 mK early on.

High QSO-like source contribution dampens but does not erase absorption.

Early reionization signals have higher signal-to-noise ratios.

Abstract

We present simulations of the 21-cm signal during the epoch of reionization. We focus on properly modeling the absorption regime in the presence of inhomogeneous Wouthuysen-Field effect and X-ray heating. We ran radiative transfer simulations for three bands in the source spectrum (Lyman, UV, and X-ray) to fully account for these processes. We find that the brightness temperature fluctuation of the 21 cm signal has an amplitude greater than 100 mK during the early reionization, up to 10 times greater than the typical amplitude of a few 10 mK obtained during the later emission phase. More importantly, we find that even a rather high contribution from QSO-like sources only damps the absorption regime without erasing it. Heating the IGM with X-ray takes time. Our results show that observations of the early reionization will probably benefit from a higher signal-to-noise value than during later stages. After analyzing the statistical properties of the signal (power spectrum and PDF) we find three diagnostics to constrain the level of X-ray, hence the nature of the first sources.