Intensity mapping of Loeb-Rybicki haloes from scattering of galactic Lyman-$α$ emission by the diffuse intergalactic medium before reionization

Abstract

We use the inferred evolution of Lyman-$α$ luminosities of galaxies in the redshift range of $z \sim 9-16$ from the James Webb Space Telescope (JWST) data to predict the power spectrum of Loeb-Rybicki haloes formed by the scattering of Lyman-$α$ photons from neutral hydrogen gas in the intergalactic medium expanding with the Hubble flow, until they Doppler shift out of resonance and escape towards the observer. This leads to the formation of the so-called Loeb-Rybicki intergalactic haloes, which are expected to be prominent even before the epoch of reionization. We find excellent prospects for a statistical detection of the intensity mapping signal from the clustering of these haloes, with current and future experiments such as the SPHEREx and CDIM. We also describe the detectability of the signal in cross-correlation with the 21-cm emission from the neutral hydrogen in the intergalactic medium at these redshifts. We find that the cross-correlation signal should be detectable at a significance of a few to a few tens of standard deviations out to $z \sim 13$ and marginally out to $z \sim 16$, using the above experiments in combination with the Square Kilometre Array (SKA)-LOW and its pathfinder, the Murchison Widefield Array (MWA).