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Astron. Astrophys. 325, 1259-1263

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The Lyman continuum radiation escaping from galaxies

J.-M. Deharveng, S. Faïsse, B. Milliard, and V. Le Brun

Laboratoire d'Astronomie Spatiale du CNRS, Traverse du Siphon, BP 8, F-13376 Marseille Cedex 12, France

Received 27 February 1997 / Accepted 8 April 1997


The H FORMULA luminosity density of galaxies is used to calculate the local diffuse radiation field at the Lyman limit as resulting from star formation in the universe. The fraction of Lyman continuum radiation leaking out from galaxies through their neutral hydrogen is the most uncertain parameter of the calculation. A comparison of the diffuse radiation predicted from galaxies with that measured from all sources of ionization shows that the average Lyman continuum escape fraction should be lower than 1%. This number is lower than the upper limits reported so far in a few objects. It is also shown that the luminosity density at the Lyman limit resulting from star formation is consistent with the luminosity density and the diffuse background measured in the far (non-ionizing) ultraviolet.

Key words: galaxies: evolution - intergalactic medium - quasars: absorption lines - galaxies: stellar content

Send offprint requests to: J.-M. Deharveng, jmd@astrsp-mrs.fr

© European Southern Observatory (ESO) 1997

Online publication: September 9, 1997
Last change: April 28, 1998