The correlation between the distribution of galaxies and 21-cm emission at high redshifts

Abstract

Deep surveys have recently discovered galaxies at the tail end of the epoch of reionization. In the near future, these discoveries will be complemented by anew generation of low-frequency radio observatories that will map the distribution of neutral hydrogen in the intergalactic medium through its redshifted 21-cm emission. In this paper we calculate the expected cross-correlation between the distribution of galaxies and intergalactic 21-cm emission at high redshifts. We demonstrate using a simple model that overdense regions are expected to be ionized early as a result of their biased galaxy formation. This early phase leads to an anticorrelation between the 21-cm emission and the overdensities in galaxies, matter and neutral hydrogen. Existing Lyα surveys probe galaxies that are highly clustered in overdense regions. By comparing 21-cm emission from regions near observed galaxies to those away from observed galaxies, future observations will be able to test this generic prediction and calibrate the ionizing luminosity of high-redshift galaxies.