Modeling the Pan-Spectral Energy Distribution of Starburst Galaxies. III. Emission Line Diagnostics of Ensembles of Evolving H II Regions

Space Telescope Science Institute, Baltimore, Maryland, United States
The Astrophysical Journal Supplement Series (Impact Factor: 11.22). 12/2008; 167(2):177. DOI: 10.1086/508261
Source: arXiv


We build, as far as theory will permit, self-consistent model H II regions around central clusters of aging stars. These produce strong emission line diagnostics applicable to either individual H II regions in galaxies or to the integrated emission line spectra of disk or starburst galaxies. The models assume that the expansion and internal pressure of individual H II regions is driven by the net input of mechanical energy from the central cluster, be it through winds or supernova events. This eliminates the ionization parameter as a free variable, replacing it with a parameter that depends on the ratio of the cluster mass to the pressure in the surrounding interstellar medium. These models explain why H II regions with low abundances have high excitation and demonstrate that at least part of the warm ionized medium is the result of overlapping faint, old, large, and low-pressure H II regions. We present line ratios (at both optical and IR wavelengths) that provide reliable abundance diagnostics for both single H II regions or for integrated galaxy spectra, and we find a number that can be used to estimate the mean age of the cluster stars exciting individual H II regions.

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