The High-Redshift Neutral Hydrogen Signature of an Anisotropic Matter Power Spectrum

TL;DR

This paper predicts how anisotropies in the matter power spectrum at high redshift could be detected through 21cm hydrogen line observations, especially with future radio telescopes like SKA.

Contribution

It provides the first detailed calculation of the expected 21cm power spectrum signature of anisotropic matter fluctuations at high redshift and assesses detectability with upcoming experiments.

Findings

SKA can marginally detect anisotropic signals at z~17 before reionization

Reionization enhances the detectability of anisotropy signals

Higher redshift and sensitivity enable percent-level measurements of anisotropy

Abstract

An anisotropic power spectrum will have a clear signature in the 21cm radiation from high-redshift hydrogen. We calculate the expected power spectrum of the intensity fluctuations in neutral hydrogen from before the epoch of reionization, and predict the accuracy to which future experiments could constrain a quadrupole anisotropy in the power spectrum. We find that the Square Kilometer Array will have marginal detection abilities for this signal at z~17 if the process of reionization has not yet started; reionization could enhance the detectability substantially. Pushing to higher redshifts and higher sensitivity will allow highly precise (percent level) measurements of anisotropy.