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

TL;DR

This paper presents advanced theoretical models for star-forming galaxies, incorporating detailed physics to better match observed emission line ratios, especially at low metallicities, and discusses their limitations and future improvements.

Contribution

Introduces a new suite of models with improved physics for star-forming galaxies, addressing low metallicity environments and comparing with extensive observational data.

Findings

Models with continuous star formation match observed line ratios.

Current models underestimate the hardness of the ionizing radiation field.

Discrepancies in [SII] fluxes highlight areas for future model improvements.

Abstract

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 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 the low-metallicity sample. 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.