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 \cH2/k2. 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 Hα 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.
@article{arxiv.2009.06197,
title = {Detecting the relativistic bispectrum in 21cm intensity maps},
author = {Sheean Jolicoeur and Roy Maartens and Eline M. De Weerd and Obinna Umeh and Chris Clarkson and Stefano Camera},
journal= {arXiv preprint arXiv:2009.06197},
year = {2021}
}