Comparison of H II region luminosities with observed stellar ionizing sources in the Large Magellanic Cloud

Abstract

We estimate the total predicted Lyman continuum emission rates of OB associations for which the complete census of O star spectral types exists. The results are compared to the observed Hα luminosities of the host H II regions. We find evidence for substantial leakage of ionizing photons from some H II regions, while others appear to be radiation-bounded. We estimate that overall for the LMC, 0-51 per cent of the ionizing radiation escapes the local nebulae, and would be available to ionize the diffuse, warm, ionized medium (WIM) in that galaxy. This range of values is consistent with the observed 35 per cent fraction of Hα luminosity emitted by the WIM in the LMC, as well as the corresponding fractions observed in other nearby galaxies. It is therefore possible that photoionization by O stars is indeed the dominant ionization mechanism for the WIM. © 1997 RAS.