Measuring the cosmic expansion rate using 21-cm velocity acoustic oscillations

TL;DR

This paper demonstrates that 21-cm velocity acoustic oscillations can serve as standard rulers to measure the cosmic expansion rate at high redshifts with high precision, using simulations tailored for the HERA telescope.

Contribution

It extends previous work by using a modified 21cmFAST code to forecast H(z) measurements from VAOs, accounting for astrophysical effects and foregrounds, achieving high accuracy at z=11-20.

Findings

H(z) can be measured with 0.3-6% accuracy using HERA.

Uncertainties in Planck parameters limit measurement errors to 0.08-0.2%.

Method can help address the Hubble Tension.

Abstract

The fluctuations in the dark matter-baryon relative velocity field are imprinted as acoustic oscillations in the 21-cm power spectrum during cosmic dawn (CD). These velocity acoustic oscillations (VAOs) keep the imprints of the comoving sound horizon scale. In a previous work by Mu\~noz, it has been demonstrated that these VAOs can be treated as standard rulers to measure the cosmic expansion rate at high redshifts by considering a variety of Lyman-Werner feedback strengths and foreground contamination scenarios. Here we extend that analysis by using a modified version of the public code \texttt{21cmFAST}. We use this code to simulate the VAOs in 21-cm power spectrum and forecast the potential to constrain $H(z)$ with the HERA radio telescope, taking into account the effects of Lyman-$\alpha$ heating, Lyman-Werner feedback and foregrounds, the dependence on various astrophysical parameters, and the degeneracy with cosmological parameters. We find that $H(z)$ can be measured with HERA at $\sim 0.3-6\%$ relative accuracy in the range $11 < z < 20$, under different astrophysical and foreground scenarios, with uncertainties in the Planck cosmological parameters setting a $\sim 0.08-0.2\%$ relative-error floor in the measurement. This accuracy is on par with most low-redshift measurements and can be helpful in testing various cosmological scenarios motivated by the ongoing ``Hubble Tension".