The correlation between star formation and 21-cm emission during the reionization epoch

Abstract

Reionization is thought to be dominated by low-i-nass galaxies, while direct observations of resolved galaxies probe only the most massive, rarest objects. The cross-correlation between fluctuations in the surface brightness of the cumulative Ly alpha emission (which serves as a proxy for the star formation rate) and the redshifted 21-cm signal from neutral hydrogen in the intergalactic medium (IGM) will directly probe the causal link between the production of ionizing photons in galaxies and the reionization of the IGM. We discuss the prospects for detecting this cross-correlation for unresolved galaxies. We find that on angular scales less than or similar to 10 arcmin detection will be practical using wide-field near-infrared (near-IR) imaging from space in combination with the forthcoming Mileura Wide-field Array - Low Frequency Demonstrator. When redshifted 21-cm observations of the neutral IGM are combined with space-based near-IR imaging of Ly alpha emission, the detection on angular scales less than or similar to 3 arcmin will be limited by the sensitivity of the 21-cm signal, even when a small-aperture optical telescope (similar to 2 m) and a moderate field of view (similar to 10 deg(2)) are used. On scales 3 arcmin, the measurement of cross-correlation will be limited by the accuracy of the foreground sky subtraction.