Full-sky bispectrum in redshift space for 21cm intensity maps

TL;DR

This paper calculates the three-point correlation function (bispectrum) of 21cm intensity maps in redshift space, demonstrating its detectability with upcoming radio telescopes like SKA and HIRAX, and emphasizing the importance of redshift-space distortions.

Contribution

It provides the first detailed computation of the full-sky bispectrum in redshift space for 21cm intensity mapping, including observational effects and noise estimates.

Findings

Redshift-space distortions dominate the bispectrum signal.

The bispectrum is detectable by SKA and HIRAX at lower redshifts.

Lensing contributions are negligible in the considered setup.

Abstract

We compute the tree-level bispectrum of 21cm intensity mapping after reionisation. We work in the directly observable angular and redshift space, focusing on equal-redshift correlations and thin redshift bins, for which the lensing contribution is negligible. We demonstrate the importance of the contributions from redshift-space distortions which typically dominate the result. Taking into account the effects of telescope beams and foreground cleaning, we estimate the signal to noise and show that the bispectrum is detectable by both SKA in single-dish mode and HIRAX in interferometer mode, especially at the lower redshifts in their respective ranges.