1999/03/31 by George B. Rybicki, Abraham Loeb
Engineering · Physics and Astronomy · #Cosmology and Gravitation Theories #Galaxies: Formation, Evolution, Phenomena #Space Technology and Applications #astro-ph
paper · pdf · doi:10.1086/312155
8 pages, 2 Postscript figures, accepted by Astrophysical Journal Letters; some typos corrected; added two paragraphs at the end of section 3 concerning detectability of Lyman alpha halos
arxiv created 1999/06/04 · openalex publication_date 1999/08/01 · arxiv updated 2009/12/01 · openalex created_date 2019/06/27 · openalex updated_date 2026/08/04
In Loeb & Rybicki (hereafter Paper I), it was shown that before reionization, the scattering of Lyα photons from a cosmological source might lead to a fairly compact (~15'') Lyα halo around the source. Observations of such halos could constrain the properties of the neutral intergalactic medium and, in particular, yield the cosmological density parameters of baryons and matter on scales where the Hubble flow is unperturbed. Paper I did not treat the polarization of this scattered radiation but did suggest that the degree of such polarization might be large. In this Letter, we report on improved calculations for these Lyα halos, now accounting for the polarization of the radiation field. The polarization is linear and is oriented tangentially to the projected displacement from the center of the source. The degree of polarization is found to be 14% at the core radius, where the intensity has fallen to half of the central value. It rises to 32% and 45% at the radii where the intensity has fallen to one-tenth and one-hundredth of the central intensity, respectively. At larger radii, the degree of polarization rises further, asymptotically to 60%. Such high values of polarization should be easily observable and provide a clear signature of the phenomenon of Lyα halos surrounding sources prior to reionization.