Can the reionization epoch be detected as a global signature in the cosmic background?

TL;DR

This paper discusses the potential to detect the epoch of reionization through a global signature in the cosmic background, focusing on radio and optical/near-IR signals caused by hydrogen transitions, which could be distinguished from foregrounds.

Contribution

It proposes a method to identify reionization signatures as sharp spectral features in the cosmic background, emphasizing the detectability with small radio telescopes and space-based optical/IR observations.

Findings

Reionization leaves a detectable spectral step in the sky background.

Radio detection is feasible with small telescopes due to the signal's amplitude.

Optical/near-IR detection requires space telescopes with low background noise.

Abstract

The reionization of the Universe is expected to leave a signal in the form of a sharp step in the spectrum of the sky. If reionization occurs at 5 < z < 20, a feature should appear in the radio sky at 70 - 240 MHz due to redshifted HI 21-cm line emission, accompanied by another feature in the optical/near-IR at 0.7 - 2.6 micron due to hydrogen recombination radiation. The expected amplitude is well above fundamental detection limits, and the sharpness of the feature may make it distinguishable from variations due to terrestrial, galactic and extragalactic foregrounds. Because this is essentially a continuum measurement of a signal which occurs over the whole sky, relatively small telescopes may suffice for detection in the radio. In the optical/near-IR, a space telescope is needed with the lowest possible background conditions, since the experiment will be severely background-limited.