The 21-cm Signal from the Cosmological Epoch of Recombination

Abstract

The redshifted 21-cm emission by neutral hydrogen offers a unique tool for mapping structure formation in the early universe in three dimensions. Here we provide the first detailed calculation of the 21-cm emission signal during and after the epoch of hydrogen recombination in the redshift range of z ~ 500-1,100, corresponding to observed wavelengths of 100-230 meters. The 21-cm line deviates from thermal equilibrium with the cosmic microwave background (CMB) due to the excess Ly-alpha radiation from hydrogen and helium recombinations. The resulting 21-cm signal reaches a brightness temperature of a milli-Kelvin, orders of magnitude larger than previously estimated. Its detection by a future lunar or space-based observatory could improve dramatically the statistical constraints on the cosmological initial conditions compared to existing two-dimensional maps of the CMB anisotropies.

Accepted for publication in JCAP, 12 pages, 3 figures

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• A Tale of Two Paradigms: the Mutual Incommensurability of LCDM and MOND
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• Supersonic Relative Velocity between Dark Matter and Baryons: A Review
• The Detectability of Radio Auroral Emission from Proxima B
• Cosmic mysteries and the hydrogen 21-cm line: bridging the gap with lunar observations
• RHINO: A large horn antenna for detecting the 21cm global signal
• The ultimate frontier of 21cm cosmology