Astronomy and Astrophysics – Astrophysics
Scientific paper
May 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...426l..65s&link_type=abstract
Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X), vol. 426, no. 2, p. 65-68
Astronomy and Astrophysics
Astrophysics
7
Far Ultraviolet Radiation, Intergalactic Media, Neutrinos, Opacity, Quasars, Ultraviolet Absorption, Universe, Astronomical Models, Cosmic X Rays, Lyman Alpha Radiation, Radioactive Decay
Scientific paper
The anomalously low value of the H I/ He I abundance ratio found by Reimers and Vogel in three Lyman limit systems has been attributed by Sciama to decay photons from intergalactic neutrinos, which can ionize H I but not He I. This explanation would not work unless the intergalactic background flux beyond the He II edge is large enough to maintain a relatively low He II opacity for the whole universe, so that (He II)/(He III) approximately 0.1 in these Lyman limit systems. In this paper we point out that this condition would be satisfied if most ASOs possess a Guilbert-Rees thermal bump with T approximately 50 eV in their soft X-ray spectra, resulting from the reprocessing of harder X-rays from the QSOs by optically thick cold material in their central regions. Several predictions of this reprocessing model have recently been verified. The resulting excess soft X-ray flux might also account for the abundances of N V and O VI observed in the Lyman limit systems and in the outer halo of our Galaxy. Our requirement that the universe has a relatively low He II opacity could be tested by a refurbished Hubble Space Telescope and by the forthcoming flight of the Hopkins Ultraviolet Telescope on Astro-2.
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