The Correlation Between Star Formation and 21cm Emission During the Reionization Epoch

TL;DR

This paper explores the potential for detecting the correlation between star formation activity, traced by Ly-alpha emission, and the 21cm signal from neutral hydrogen during reionization, using upcoming observational facilities.

Contribution

It assesses the feasibility of measuring the cross-correlation between Ly-alpha emission and 21cm signals during reionization with future space-based and radio observations.

Findings

Detection is feasible on <10 arc-minute scales with upcoming widefield near-IR and radio arrays.

On <3 arc-minute scales, sensitivity limits detection despite moderate-sized telescopes.

Foreground subtraction accuracy is the main challenge for larger angular scale measurements.

Abstract

Reionization is thought to be dominated by low mass 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 21cm 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 <10 arc-minutes, detection will be practical using widefield near-IR imaging from space in combination with the forthcoming Mileura Widefield Array - Low Frequency Demonstrator. When redshifted 21cm observations of the neutral IGM are combined with space-based near-IR imaging of Ly-alpha emission, the detection on angular scales <3 arc-minutes will be limited by the sensitivity of the 21cm signal, even when a small aperture optical telescope (~2m) and a moderate field of view (~10 square degrees) are used. On scales >3 arc-minutes, the measurement of cross-correlation will be limited by the accuracy of the foreground sky subtraction.