paper

Luminosity indicators in dusty photoionized environments

arXiv:astro-ph/9806130 · doi:10.1086/316222

Abstract

The luminosity of the central source in ionizing radiation is an essential parameter in a photoionized environment, and one of the most fundamental physical quantities one can measure. We outline a method of determining luminosity for any emission-line region using only infrared data. In dusty environments, grains compete with hydrogen in absorbing continuum radiation. Grains produce infrared emission, and hydrogen produces recombination lines. We have computed a very large variety of photoionization models, using ranges of abundances, grain mixtures, ionizing continua, densities, and ionization parameters. The conditions were appropriate for such diverse objects as H II regions, planetary nebulae, starburst galaxies, and the narrow and broad line regions of active nuclei. The ratio of the total thermal grain emission relative to H (IR/H) is the primary indicator of whether the cloud behaves as a classical Strömgren sphere (a hydrogen-bounded nebula) or whether grains absorb most of the incident continuum (a dust-bounded nebula). We find two global limits: when infrared recombination lines determine the source luminosity in ionizing photons; when the grains act as a bolometer to measure the luminosity.

12 pages 3 figures. Accepted ASP Sept.98

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