Redshift-space distortions in simulations of the 21-cm signal from the cosmic dawn

TL;DR

This study uses numerical simulations to analyze how redshift-space distortions affect the 21-cm signal from the Cosmic Dawn, revealing their impact on detectability and anisotropy, and demonstrating potential for imaging this epoch with SKA observations.

Contribution

It provides the first detailed analysis of redshift-space distortions on the 21-cm signal during the Cosmic Dawn using fully numerical radiative transfer simulations.

Findings

RSDs boost the 21-cm power spectrum, improving detection prospects.

RSDs cause anisotropy in the signal during certain epochs.

Simulations suggest SKA can image the Cosmic Dawn despite RSD effects.

Abstract

The 21-cm signal from the Cosmic Dawn (CD) is likely to contain large fluctuations, with the most extreme astrophysical models on the verge of being ruled out by observations from radio interferometers. It is therefore vital that we understand not only the astrophysical processes governing this signal, but also other inherent processes impacting the signal itself, and in particular line-of-sight effects. Using our suite of fully numerical radiative transfer simulations, we investigate the impact on the redshifted 21-cm from the CD from one of these processes, namely the redshift-space distortions (RSDs). When RSDs are added, the resulting boost to the power spectra makes the signal more detectable for our models at all redshifts, further strengthening hopes that a power spectra measurement of the CD will be possible. RSDs lead to anisotropy in the signal at the beginning and end of the CD, but not while X-ray heating is underway. The inclusion of RSDs, however, decreases detectability of the non-Gaussianity of fluctuations from inhomogeneous X-ray heating measured by the skewness and kurtosis. On the other hand, mock observations created from all our simulations that include telescope noise corresponding to 1000 h observation with the Square Kilometre Array telescope show that we may be able image the CD for all heating models considered and suggest RSDs dramatically boost fluctuations coming from the inhomogeneous Ly-$\alpha$ background.