The magnitude of the dark ages 21-cm signal in the context of existing early and late time constraints on $Λ$CDM

Abstract: The dark ages 21-cm signal is a promising probe of the currently unobserved infant universe between the formation of the Cosmic Microwave Background around $z \approx 1100$ and the first galaxies around $z\approx 30$. A detection of the signal will help researchers understanding the nature of dark matter and dark energy, the expansion of the universe and any extensions to the concordance $Λ$CDM model that could explain the reported Cosmic Dawn 21-cm signal from EDGES and the Hubble tension. In this letter we take existing constraints on the $Λ$CDM cosmological model from two early time probes, Planck and WMAP, and two late time probes, DES galaxy lensing and clustering and Baryon Acoustic Oscillations, and propagate these through to constraints on the magnitude of the dark ages 21-cm signal. We constrain the magnitude and central frequency of the signal while methodically accounting for uncertainties in the cosmological parameters. We find that within the context of our modelling assumptions and the $Λ$CDM paradigm, the depth of the dark ages 21-cm signal is known to better than 1 mK and the central frequency to within 0.05 MHz.