Constraining High Redshift X-ray Sources with Next Generation 21 cm Power Spectrum Measurements

TL;DR

This paper predicts how next-generation 21 cm power spectrum measurements can constrain the properties of early X-ray sources and improve understanding of cosmic reionization, even with observational challenges.

Contribution

It provides quantitative forecasts of constraints on high-redshift X-ray sources using Fisher matrix analysis and simulations for upcoming radio arrays like HERA and SKA.

Findings

HERA and SKA can constrain X-ray source properties to within 10%.

Power spectrum signatures extend beyond the reionization peak due to spin temperature fluctuations.

Heating epoch observations help break degeneracies, improving reionization parameter estimates.

Abstract

We use the Fisher matrix formalism and semi-numerical simulations to derive quantitative predictions of the constraints that power spectrum measurements on next-generation interferometers, such as the Hydrogen Epoch of Reionization Array (HERA) and the Square Kilometre Array (SKA), will place on the characteristics of the X-ray sources that heated the high redshift intergalactic medium. Incorporating observations between $z=5$ and $z=25$, we find that the proposed 331 element HERA and SKA phase 1 will be capable of placing $\lesssim 10\%$ constraints on the spectral properties of these first X-ray sources, even if one is unable to perform measurements within the foreground contaminated "wedge" or the FM band. When accounting for the enhancement in power spectrum amplitude from spin temperature fluctuations, we find that the observable signatures of reionization extend well beyond the peak in the power spectrum usually associated with it. We also find that lower redshift degeneracies between the signatures of heating and reionization physics lead to errors on reionization parameters that are significantly greater than previously predicted. Observations over the heating epoch are able to break these degeneracies and improve our constraints considerably. For these two reasons, 21\,cm observations during the heating epoch significantly enhance our understanding of reionization as well.