The Magnitude of the Dark Ages 21 cm Signal in the Context of Existing Early and Late Time Constraints on ΛCDM

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 ≈ 1100 and the first galaxies around z ≈ 30. A detection of the signal will help researchers understand the nature of dark matter and dark energy, the expansion of the Universe, and any extensions to the concordance ΛCDM 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 ΛCDM cosmological model from two early time probes, Planck and the Wilkinson Microwave Anisotropy Probe, and two late time probes, Dark Energy Survey 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 modeling assumptions and the ΛCDM 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.