Astrophysical information from the Rayleigh-Jeans Tail of the CMB

One of the explanations for the recent EDGES-LOW band 21cm 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 x 10(48) erg per solar mass in stars are required along with a suppression of star formation in halos with virial temperatures less than or similar to 2 x 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)] x 13.8 Gyr, [10(-12.2), 10(-10)] eV and [10(-7),10(-5.6)] respectively. This implies an excess radio background which is approximate to 5.7 times stronger than the CMB around 80 MHz. This value is a factor similar to 3 higher than the previous predictions which used a simplified model for the 21 cm signal.

Automated summary

One possible explanation for the recent measurements of a strong absorption signal around 80 MHz is the presence of an excess radio background. This excess could be caused by the decay of unstable particles into dark photons with a mixing angle with electromagnetism. The measurements are used to derive constraints on the properties of early galaxies and the parameters of the particle physics model. The results suggest a high star formation efficiency, suppression of star formation in certain halos, and specific ranges for the mass and lifetime of the decaying dark matter particles, dark photon mass, and mixing angle.