1999/02/28 by Abraham Loeb, G. B. Rybicki, George Rybicki · 3 citations
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #Galaxies: Formation, Evolution, Phenomena #Radio Astronomy Observations and Technology #astro-ph
paper · pdf · doi:10.1086/307844
published as Astrophys.J.524:527-535,1999 · 21 pages, 5 Postscript figures, accepted by ApJ; figures 1--3 corrected; new section added on the detectability of Lyman alpha halos; conclusions updated
arxiv created 1999/06/04 · openalex publication_date 1999/10/20 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/04
The spectra of the first galaxies and quasars in the universe should be strongly absorbed shortward of their rest-frame Lyα wavelength by neutral hydrogen (H I) in the intervening intergalactic medium. However, the Lyα line photons emitted by these sources are not eliminated but rather scatter until they redshift out of resonance and escape owing to the Hubble expansion of the surrounding intergalactic H I. We calculate the resulting brightness distribution and the spectral shape of the diffuse Lyα line emission around high-redshift sources before the intergalactic medium was reionized. Typically, the Lyα photons emitted by a source at z s ~ 10 scatter over a characteristic angular radius of ~15'' around the source and compose a line that is broadened and redshifted by ~10 3 km s -1 relative to the source. The scattered photons are highly polarized. Detection of the diffuse Lyα halos around high-redshift sources would provide a unique tool for probing the neutral intergalactic medium before the epoch of reionization. On sufficiently large scales, where the Hubble flow is smooth and the gas is neutral, the Lyα brightness distribution can be used to determine the cosmological mass densities of baryons and matter.