On the detection of a cosmic dawn signal in the radio background

Understand

The astrophysics of cosmic dawn, when star formation commenced in the first collapsed objects, is predicted to be revealed as spectral and spatial signatures in the cosmic radio background at long wavelengths.

• The sky-averaged redshifted 21-cm absorption line of neutral hydrogen is a probe of cosmic dawn.
• The line profile is determined by the evolving thermal state of the gas, radiation background, Lyman-$\alpha$ radiation from stars scattering off cold primordial gas and the relative populations of the hyperfine spin levels in neutral hydrogen atoms.
• We report a radiometer measurement of the spectrum of the radio sky in the 55--85~MHz band, which shows that the profile found by Bowman et al.