A lower limit of dz > 0.06 for the duration of the reionization epoch

TL;DR

This paper presents an all-sky 21-centimetre spectrum that constrains the duration of the cosmic reionization epoch, ruling out very rapid reionization with dz less than 0.06.

Contribution

It provides the first direct observational lower limit on the duration of reionization using global 21-cm measurements.

Findings

Excludes rapid reionization with dz < 0.06 at 95% confidence

Provides all-sky spectrum data between 100-200 MHz

Constrains the timeline of the epoch of reionization

Abstract

Observations of the 21-centimetre line of atomic hydrogen in the early Universe directly probe the history of the reionization of the gas between galaxies. The observations are challenging, though, because of the low expected signal strength (~10 mK), and contamination by strong (>100 K) foreground synchrotron emission in the Milky Way and extragalactic continuum sources2. If reionization happened rapidly, there should be a characteristic signature visible against the smooth foreground in an all-sky spectrum. Here we report an all-sky spectrum between 100 and 200 MHz, corresponding to the redshift range 6 < z < 13 for the 21-centimetre line. The data exclude a rapid reionization timescale of dz < 0.06 at the 95% confidence level.