Oxygen Abundance Throughout the Dwarf Starburst IC 10

TL;DR

This study maps the oxygen abundance in the starburst dwarf galaxy IC 10, revealing a wide range of metallicities and highlighting the limitations of strong line methods in such dynamic environments.

Contribution

First direct measurements of oxygen abundance in IC 10 using auroral lines, showing the galaxy's poorly mixed ISM and limitations of R23 abundance estimates.

Findings

Median oxygen abundance is 8.37 with a standard deviation of 0.25.

Weak correlations between oxygen abundance and HII region properties.

Large abundance variation indicates a poorly mixed ISM.

Abstract

Measurements of oxygen abundance throughout galaxies provide insight to the formation histories and ongoing processes. Here we present a study of the gas phase oxygen abundance in the HII regions and diffuse gas of the nearby starburst dwarf galaxy, IC 10. Using the Keck Cosmic Web Imager (KCWI) at W.M. Keck Observatory, we map the central region of IC 10 from 3500-5500A. The auroral [OIII]4363A line is detected with high signal-to-noise in 12 of 46 HII regions observed, allowing for direct measurement of the oxygen abundance, yielding a median and standard deviation of $\rm12+log(O/H)=8.37\pm0.25$. We investigate trends between these directly measured oxygen abundances and other HII region properties, finding weak negative correlations with the radius, velocity dispersion, and luminosity. We also find weak negative correlations between oxygen abundance and the derived quantities of turbulent pressure and ionized gas mass, and a moderate correlation with the derived dynamical mass. Strong line, $\rm R_{23}$ abundance estimates are used in the remainder of the HII regions and on a resolved spaxel-by-spaxel basis. There is a large offset between the abundances measured with $\rm R_{23}$ and the auroral line method. We find that the $\rm R_{23}$ method is unable to capture the large range of abundances observed via the auroral line measurements. The extent of this variation in measured abundances further indicates a poorly mixed interstellar medium (ISM) in IC 10, which is not typical of dwarf galaxies and may be partly due to the ongoing starburst, accretion of pristine gas, or a late stage merger.