Measuring the Redshift of Reionization with a Modest Array of Low-Frequency Dipoles

Understand

The designs of the first generation of cosmological 21-cm observatories are split between single dipole experiments which integrate over a large patch of sky in order to find the global (spectral) signature of reionization, and interferometers with arcminute-scale angular resolution whose goal is to measure the 3D power spectrum of ionized regions during reionization.

• We examine whether intermediate scale instruments with complete Fourier (uv) coverage are capable of placing new constraints on reionization.
• We find that even without using a full power spectrum analysis, the global redshift of reionization, z_reion, can in principle be measured from the variance in the 21-cm signal among multiple beams as a function of frequency at a roughly 1 degree angular scale.
• At this scale, the beam-to-beam variance in the differential brightness temperature peaks when the average neutral fraction was around 50%, providing a convenient flag of z_reion.