The anomalous 21-cm absorption at high redshifts

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 lesssim 230 mK. Nevertheless, the line profile’s redshift range (15lesssim zlesssim 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–Lemaître–Robertson–Walker cosmology known as the R_{mathrm{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 zsim 16. We find that the requirements for this process to have occurred would have self-consistently established an equilibrium spin temperature T_{mathrm{s}}approx 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 (sim 3.3 K) inferred from the 21-cm absorption feature appears to be much more consistent with the R_{mathrm{h}}=ct profile than that implied by Lambda CDM, for which adiabatic cooling would have established a spin temperature T_mathrm{s}(z=17.2)sim 6 K.