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

Abstract

We revisit the 21 cm power spectrum from the epoch of cosmic dawn in light of the recent Experiment to Detect the Global Epoch of reionization Signature (EDGES) detection of the 21 cm global signal at frequencies corresponding to z  ∼ 20. 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 ≲ z ≲ 21). We therefore consider models in which the ultraviolet photons were dominantly produced in the rarest and most massive halos ( M ≳ 10 9 M ⊙ ), as 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 cosmic microwave background and Ly α photons due to the large shot noise associated with the rare sources. The power spectrum is enhanced by more than an order of magnitude compared to previous models that did not include the shot-noise contribution, making it a promising target for upcoming radio interferometers that aim to detect high-redshift 21 cm fluctuations.