Astrophysical information from the Rayleigh-Jeans Tail of the CMB

TL;DR

This paper uses EDGES-LOW band measurements to constrain early galaxy properties and particle physics models explaining an excess radio background, suggesting a stronger background than previously estimated.

Contribution

It provides joint constraints on early galaxy parameters and decaying dark matter properties using Bayesian analysis of 21-cm data, incorporating a detailed particle physics model.

Findings

Excess radio background is about 5.7 times stronger than the CMB at 80 MHz.

High star formation efficiency and specific X-ray emission levels are required.

Dark matter particle properties are constrained within specific mass, lifetime, and mixing angle ranges.

Abstract

One of the explanations for the recent EDGES-LOW band 21-cm measurements of a strong absorption signal around 80~MHz is the presence of an excess radio background to the Cosmic Microwave Background (CMB). Such excess can be produced by the decay of unstable particles into small mass dark photons which have a non-zero mixing angle with electromagnetism. We use the EDGES-LOW band measurements to derive joint constraints on the properties of the early galaxies and the parameters of such a particle physics model for the excess radio background. A Bayesian analysis shows that a high star formation efficiency and X-ray emission of $4-7 \times 10^{48} ~\rm erg$ per solar mass in stars are required along with a suppression of star formation in halos with virial temperatures $\lesssim 2\times 10^4$ K. The same analysis also suggests a 68 percent credible intervals for the mass of the decaying dark matter particles, it's lifetime, dark photon mass and the mixing angle of the dark and ordinary photon oscillation of $[10^{-3.5}, 10^{-2.4}]$ eV, $[10^{1.1}, 10^{2.7}]\times 13.8 ~\rm Gyr$, $[10^{-12.2}, 10^{-10}]$ eV and $[10^{-7}, 10^{-5.6}]$ respectively. This implies an excess radio background which is $\approx 5.7$ times stronger than the CMB around 80~MHz. This value is a factor $\sim 3$ higher than the previous predictions which used a simplified model for the 21-cm signal.