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

Understand

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.