Cosmological constraints from 21cm surveys after reionization

TL;DR

This paper forecasts the potential of post-reionization 21cm surveys to significantly improve cosmological parameter constraints, outperforming some CMB experiments, with results depending on survey design and astrophysical uncertainties.

Contribution

It provides a detailed Fisher matrix forecast for 21cm post-reionization surveys, comparing two designs and analyzing their potential to constrain cosmological parameters.

Findings

Post-reionization 21cm surveys can outperform next-generation CMB experiments in constraining key parameters.

Constraints on Ω_Λ, Ω_m h^2, and Ω_ν h^2 are improved by at least an order of magnitude over Planck.

Astrophysical uncertainties have less impact during post-reionization compared to epoch of reionization.

Abstract

21cm emission from residual neutral hydrogen after the epoch of reionization can be used to trace the cosmological power spectrum of density fluctuations. Using a Fisher matrix formulation, we provide a detailed forecast of the constraints on cosmological parameters that are achievable with this probe. We consider two designs: a scaled-up version of the MWA observatory as well as a Fast Fourier Transform Telescope. We find that 21cm observations dedicated to post-reionization redshifts may yield significantly better constraints than next generation Cosmic Microwave Background (CMB) experiments. We find the constraints on $\Omega_\Lambda$, $\Omega_{\rm m}h^2$, and $\Omega_\nu h^2$ to be the strongest, each improved by at least an order of magnitude over the Planck CMB satellite alone for both designs. Our results do not depend as strongly on uncertainties in the astrophysics associated with the ionization of hydrogen as similar 21cm surveys during the epoch of reionization. However, we find that modulation of the 21cm power spectrum from the ionizing background could potentially degrade constraints on the spectral index of the primordial power spectrum and its running by more than an order of magnitude. Our results also depend strongly on the maximum wavenumber of the power spectrum which can be used due to non-linearities.