We have used the H luminosity density of galaxies in the local universe for estimating the contribution of galaxies to the ionizing background at . This approach reduces the number of theoretical assumptions entering this type of evaluation and is therefore expected to narrow the range of predicted values. Of the remaining parameters needed for the evaluation, the fraction of radiation leaking out from galaxies is the most uncertain. From a comparison between the ionizing photons predicted by on-going star formation in galaxies and those measured in the intergalactic radiation field, it is found that the escape fraction is smaller than 1% in the local universe. This average upper limit is more restrictive than the upper limits reported in four galaxies by Leitherer et al. (1995) and re-analyzed by Hurwitz et al. (1997).
© European Southern Observatory (ESO) 1997
Online publication: April 28, 1998