Testing gravity at large scales with H i intensity mapping

Abstract

We investigate the possibility of testing Einstein's general theory of relativity (GR) and the standard cosmological model via the EG statistic using neutral hydrogen (H i) intensity mapping. We generalize the Fourier space estimator for EG to include H i as a biased tracer of matter and forecast statistical errors using H i clustering and lensing surveys that can be performed in the near future, in combination with ongoing and forthcoming optical galaxy and cosmic microwave background (CMB) surveys. We find that fractional errors <1 per cent in the EG measurement can be achieved in a number of cases and compare the ability of various survey combinations to differentiate between GR and specific modified gravity models. Measuring EG with intensity mapping and the Square Kilometre Array can provide exquisite tests of gravity at cosmological scales.