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

TL;DR

This paper explores how the shape of the EDGES 21 cm signal implies rapid hydrogen spin temperature coupling, leading to models predicting large power spectrum amplitudes from rare, massive halos, which are promising for future detection.

Contribution

It introduces models considering rare, massive halos as dominant UV photon sources, predicting significantly enhanced 21 cm power spectrum signals due to shot noise effects.

Findings

Power spectrum amplitude is over an order of magnitude larger than previous models.

Models with rare, massive halos produce strong inhomogeneous signals.

Enhanced signals are promising targets for upcoming radio interferometers.

Abstract

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. The power spectrum is enhanced by more than an order of magnitude compared to previous models which 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.