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Astron. Astrophys. 321, 1-7 (1997)

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Comparison of stars and decaying neutrinos as additional sources of the intergalactic UV background

Luis Masperi 1 and Sandra Savaglio 2

1 Centro Atómico Bariloche and Instituto Balseiro, Comisión Nacional de Energía Atómica and Universidad Nacional de Cuyo, 8400 S.C. de Bariloche, Argentina
2 European Southern Observatory, Karl-Schwarzschildstr. 2, D-85748 Garching bei München, Germany

Received 29 April 1996 / Accepted 5 September 1996


A numerical calculation of properties of finite absorbers and of intergalactic medium based on photoionization equilibrium is performed to confront alternative UV sources in addition to quasars.

It is seen that a spectrum including a large peak around the HI ionization energy due to decaying neutrinos is too soft in the region up to the HeI edge to explain the relatively small observed ratio of neutral He and H densities in Lyman-limit systems if their size is of the kpc order. The recently proposed decrease of the contribution from unstable neutrinos solves this problem but tends to spoil the consistence between IGM and Lyman- [FORMULA] clouds, which requires a large ratio of fluxes for the HI and HeII ionization frequencies, unless there is a very fast decline of quasars above [FORMULA].

On the other hand, the addition of stars to quasars may produce a spectrum sufficiently hard between HI and HeI and thereafter soft up to HeII to allow a reasonable agreement of the properties of denser absorbers with those of IGM. This model seems to favour cold dark matter with additional cosmological constant.

Key words: dark matter – galaxies: intergalactic medium – quasars: absorption lines – diffuse radiation

Send offprint requests to: Luis Masperi

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998