Theoretical Modeling of Star-forming Galaxies I. Emission Line Diagnostic Grids for Local and Low-metallicity Galaxies

We use the newest generation of the Starburst99/Mappings code to generate an extensive suite of models to facilitate detailed studies of star-forming galaxies and their ISM properties, particularly at low metallicities. The new models used include a rigorous treatment of metal opacities in the population synthesis modeling and more detailed dust physics in the photoionization code. These models span a wide range of physical parameters including metallicity, ionization parameter, and the adoption of both a instantaneous burst and continuous star formation history. We examine the agreement between our models and local (z < 0.1) star-forming galaxy populations from several large datasets, including the Sloan Digital Sky Survey, the Nearby Field Galaxy Survey, and samples of blue compact galaxies and metal-poor galaxies. We investigate whether our new model grid can reach agreement with the ISM properties of low-metallicity environments, a task which has proven difficult in past work. We find that models adopting a continuous star formation history reproduce the metallicity-sensitive line ratios observed in the local population of star-forming galaxies, including lowmetallicity galaxies. However, we find that the current codes generate an insufficiently hard ionizing radiation field, leading to deficiencies in the [SII] fluxes produced by the models. We consider the advantages and short-comings of this suite of models, and discuss future work and improvements that can be applied to the modeling of star-forming galaxies.