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

We build, as far as theory will permit, self consistent model HII regionsaround central clusters of aging stars. These produce strong emission linediagnostics applicable to either individual HII regions in galaxies, or to theintegrated emission line spectra of disk or starburst galaxies. The modelsassume that the expansion and internal pressure of individual HII regions isdriven by the net input of mechanical energy from the central cluster, be itthrough winds or supernova events. This eliminates the ionization parameter asa free variable, replacing it with a parameter which depends on the ratio ofthe cluster mass to the pressure in the surrounding interstellar medium. Thesemodels explain why HII regions with low abundances have high excitation, anddemonstrate that at least part of the warm ionized medium is the result ofoverlapping faint, old, large, and low pressure HII regions. We present lineratios (at both optical and IR wavelengths) which provide reliable abundancediagnostics for both single HII regions or for integrated galaxy spectra, andwe find a number that can be used to estimate the mean age of the cluster starsexciting individual HII regions.Comment: 22 pages. 18 figures. Accepted for publication in Astrophysical journal Supplements. Electronic tabular material is available on request to Michael.Dopita@anu.edu.a