# Addressing the [O III]/H\b{eta} Offset of Dwarf Galaxies in the RESOLVE Survey

## TL;DR

This study investigates the persistent [O III]/Hβ offset in dwarf galaxies, demonstrating that empirical abundance scaling, cosmic ray heating, and diverse physical conditions in nebulae are crucial for accurate emission line modeling.

## Contribution

The paper introduces improved modeling techniques incorporating empirical abundances and additional heating mechanisms to better match observed emission line ratios in dwarf galaxies.

## Key findings

- Empirical abundance scaling influences thermal balance in HII regions.
- Cosmic ray heating can align models with observed line ratios.
- Diverse physical conditions improve emission line predictions.

## Abstract

Metal poor dwarf galaxies in the local universe, such as those found in the RESOLVE galaxy survey, often produce high [O III]/H\b{eta} ratios close to the star forming demarcation lines of the diagnostic BPT diagram. Modeling the emission from these galaxies at lower metallicities generally underpredicts this line ratio, which is typically attributed to a deficit of photons >35 eV. We show that applying a model that includes empirical abundances scaled with metallicity strongly influences the thermal balance in HII regions and preserves the [O III]/H\b{eta} offset even in the presence of a harder radiation field generated by interacting binaries. Additional heating mechanisms are more successful in addressing the offset. In accordance with the high sSFR typical of dwarf galaxies in the sample, we demonstrate that cosmic ray heating serves as one mechanism capable of aligning spectral synthesis predictions with observations. We also show that incorporating a range of physical conditions in our modeling can create even better agreement between model calculations and observed emission line ratios. Together these results emphasize that both the hardness of the incident continuum and the variety of physical conditions present in nebular gas clouds must be accurately accounted for prior to drawing conclusions from emission line diagnostic diagrams.