Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 1991
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991apj...376l..33m&link_type=abstract
Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X), vol. 376, Aug. 1, 1991, p. L33-L36.
Astronomy and Astrophysics
Astrophysics
48
Background Radiation, Quasars, Red Shift, Intergalactic Media, Ionizing Radiation, Photoionization
Scientific paper
Two candidates are considered for the sources of the ionizing background: primeval galaxies and AGN-type objects. The spectrum of the diffuse radiation field is computed taking into account the opacity of intervening Ly-alpha clouds and Lyman limit systems. The possibility is assessed that the QSO heavy-element absorption systems are photoionized by a metagalactic flux which is dominated by the UV radiation from hot stars in young galaxies. Grids of photoionization models for metal-line systems are presented, and it is argued that the relative column densities of the most abundant ions predicted by the models are compatible with the observational constraints. The inferred physical properties of the absorbing clouds are discussed. Given that the observed QSOs cannot provide the required number of ionizing photons at high redshift, the results obtained support a scenario in which young star-forming galaxies are the main sources of the UV radiation background at early epochs.
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