Escaping Radiation from Massive Star HII regions in the Magellanic Clouds
Department of Astronomy, University of Michigan, 500 Church St., Ann Arbor, MI, USA
Department of Astronomy, University of Michigan, 500 Church St., Ann Arbor, MI, USA
Department of Physics, Middlebury College, Middlebury, VT, USA
CTIO, Casilla 603, La Serena, Chile
CTIO, Casilla 603, La Serena, Chile
Abstract
We present a novel approach for distinguishing density-bounded vs radiation bounded HII regions based on [SII]/Halpha and [SII]/[OIII] ratio maps. We find most HII regions fall into one of three categories: radiation bounded, open blister type, and density bounded. Our approach directly diagnoses the existence of ionization fronts around massive stars, revealing a significant number of HII regions to be density bounded. Furthermore, we can place a lower limit on the fraction of ionizing photons escaping each region yielding values consistent with other methods, with direct implications for the ionization of the Warm Interstellar Medium and reionization of the universe at high redshift. We conclude that the three morphological classifications are correlated with the observed N(HI) column density and Halpha luminosity, however a more filamentary structure of the LMC does not lead to higher HII escape fractions than in the SMC.