Decaying Neutrinos and the Opacity of the Universe at the He II Edge
Abstract
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] ~ 0.1 in these Lyman limit systems. In this paper we point out that this condition would be satisfied if most QSOs possess a Guilbert-Rees thermal bump with T ~ 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 1994
- DOI:
- 10.1086/187341
- Bibcode:
- 1994ApJ...426L..65S
- Keywords:
-
- Far Ultraviolet Radiation;
- Intergalactic Media;
- Neutrinos;
- Opacity;
- Quasars;
- Ultraviolet Absorption;
- Universe;
- Astronomical Models;
- Cosmic X Rays;
- Lyman Alpha Radiation;
- Radioactive Decay;
- Astronomy;
- ELEMENTARY PARTICLES;
- GALAXIES: QUASARS: ABSORPTION LINES