Detecting the relativistic bispectrum in 21cm intensity maps

TL;DR

This paper explores the potential to detect relativistic effects in the bispectrum of 21cm intensity maps, highlighting their increased detectability compared to power spectrum signals, despite observational challenges.

Contribution

It demonstrates that relativistic effects in the bispectrum are detectable in future 21cm surveys, extending previous findings from galaxy surveys.

Findings

Relativistic bispectrum signal couples to short-scale modes.

Detection is possible with next-generation 21cm maps, despite foreground and beam challenges.

Relativistic effects are more detectable in the bispectrum than in the power spectrum.

Abstract

We investigate the detectability of leading-order relativistic effects in the bispectrum of future 21cm intensity mapping surveys. The relativistic signal arises from Doppler and other line-of-sight effects in redshift space. In the power spectrum of a single tracer, these effects are suppressed by a factor $\cH^2/k^2$. By contrast, in the bispectrum the relativistic signal couples to short-scale modes, leading to an imaginary contribution that scales as $\cH/k$, thus increasing the possibility of detection. Previous work has shown that this relativistic signal is detectable in a Stage IV H$\alpha$ galaxy survey. {We show that the signal is also detectable by next-generation 21cm intensity maps, but typically with a lower signal-to-noise, due to foreground and telescope beam effects.