Strong Hydrogen Absorption at Cosmic Dawn: the Signature of a Baryonic Universe

Abstract

The recently reported detection of redshifted 21cm absorption at $z\approx 17$ is a significant advance in the exploration of the cosmic dark ages. The observed signal ($T_{21}\approx -0.5$ K with the limit $T_{21}<-0.3$ K at 99\% c.l.) is anomalously strong for $\Lambda$CDM, which predicts at most $-0.24$ K. Here I show that the strong observed signal is expected in a purely baryonic universe.

To appear in RNAAS. 3 pages, 1 figure

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• Predictions for the sky-averaged depth of the 21cm absorption signal at high redshift in cosmologies with and without non-baryonic cold dark matter
• Overview of the ESCAPE Dark Matter Test Science Project for Astronomers
• Sensitivities on non-spinning and spinning primordial black hole dark matter with global 21 cm troughs