Publications Astronomical Society of Australia, vol. 15, no. 1, p. 83-85
Beckman, J. E.; Rozas, M.; Knapen, J. H.
Three different types of evidence are presented in favour of the hypothesis that the HII regions in disk galaxies with H-alpha luminosities greater than a critical value of 10^(38.6)^ erg s^(-1)^ are density bounded, and that the escaping Lyman continuum photons from these are the principal ionizing agents for the diffuse ISM in disk galaxies. This has important implications for the ionization of the intergalactic medium, and for computed star formation rates in spirals.