The Anomalous 21-cm Absorption at High Redshifts

TL;DR

This paper explores whether the anomalous 21-cm absorption signal at high redshift can be explained by an alternative cosmological model, the R_h=ct universe, which better fits the observed data than the standard LCDM model.

Contribution

It demonstrates that the R_h=ct cosmology can naturally account for the 21-cm absorption feature through dust rethermalization, challenging the standard cosmological interpretation.

Findings

The 21-cm signal's amplitude is inconsistent with standard cosmology.

The R_h=ct universe can explain the observed spin temperature via dust rethermalization.

Standard model rules out dust rethermalization as an explanation.

Abstract

The EDGES collaboration has reported the detection of a global 21-cm signal with a plateau centered at 76 MHz (i.e., redshift 17.2), with an amplitude of 500^(+200)_(-500) mK. This anomalous measurement does not comport with standard cosmology, which can only accommodate an amplitude < 230 mK. Nevertheless, the line profile's redshift range (15 < z < 20) suggests a possible link to Pop III star formation and an implied evolution out of the `dark ages.' Given this tension with the standard model, we here examine whether the observed 21-cm signal is instead consistent with the results of recent modeling based on the alternative Friedmann-Lemaitre-Robertson-Walker cosmology known as the R_h=ct universe, showing that--in this model--the CMB radiation might have been rethermalized by dust ejected into the IGM by the first-generation stars at redshift z < 16. We find that the requirements for this process to have occurred would have self-consistently established an equilibrium spin temperature T_s~3.4 K in the neutral hydrogen, via the irradiation of the IGM by deep penetrating X-rays emitted at the termination shocks of Pop III supernova remnants. Such a dust scenario has been strongly ruled out for the standard model, so the spin temperature (~3.3 K) inferred from the 21-cm absorption feature appears to be much more consistent with the R_h=ct profile than that implied by LCDM, for which adiabatic cooling would have established a spin temperature T_s(z=17.2)~6 K.