Constraining the unexplored period between reionization and the dark ages with observations of the global 21 cm signal

TL;DR

This paper develops a Fisher matrix approach to assess how single-dipole experiments can constrain the 21 cm signal from reionization and dark ages, highlighting the potential and challenges of such observations.

Contribution

It introduces a formalism for sensitivity analysis of 21 cm global signal observations and explores their capability to constrain early universe parameters.

Findings

Rapid reionization with delta z<2 can be constrained

Observations at 50-100 MHz can limit first stars' emissivity

Detecting dark ages signal before star formation is very difficult

Abstract

Observations of the frequency dependence of the global brightness temperature of the redshifted 21 cm line of neutral hydrogen may be possible with single dipole experiments. In this paper, we develop a Fisher matrix formalism for calculating the sensitivity of such instruments to the 21 cm signal from reionization and the dark ages. We show that rapid reionization histories with duration delta z< 2 can be constrained, provided that local foregrounds can be well modelled by low order polynomials. It is then shown that observations in the range nu = 50 - 100 MHz can feasibly constrain the Lyman alpha and X-ray emissivity of the first stars forming at z = 15 - 25, provided that systematic temperature residuals can be controlled to less than 1 mK. Finally, we demonstrate the difficulty of detecting the 21 cm signal from the dark ages before star formation.