Implication of the Shape of the EDGES Signal for the 21 cm Power Spectrum

Understand

We revisit the 21 cm power spectrum from the epoch of cosmic dawn in light of the recent EDGES detection of the 21 cm global signal at frequencies corresponding to $z\sim20$.

• The shape of the signal suggests that the spin temperature of neutral hydrogen was coupled to the kinetic temperature of the gas relatively rapidly ($19\lesssim z \lesssim 21$).
• We therefore consider models in which the UV photons were dominantly produced in the rarest and most massive halos ($M\gtrsim 10^9M_\odot$), since their abundance grows fast enough at those redshifts to account for this feature of the signal.
• We show that these models predict large power spectrum amplitudes during the inhomogeneous coupling, and then inhomogeneous heating by CMB and Lyman-$\alpha$ photons due to the large shot noise associated with the rare sources.