Affiliation: Center for Astrophysics | Harvard & Smithsonian

Contribution: Poster

Title: The Impact of Temperature and Density Inhomogeneities on the Gas-Phase Metallicity in Spatially Resolved HII Regions

Abstract: The gas-phase metallicity of the interstellar medium is critical for understanding the chemical history and evolution of a galaxy. However, the accurate determination of the gas-phase metallicity remains a challenge in galaxy evolution studies, as gas-phase metallicity measurements are based on assumptions on the physical properties of HII regions, and often fail to account for spatial variations in electron temperature and density throughout an HII region. This uncertainty is exacerbated on the scales of spatially resolved HII regions, due to the difficulty of obtaining faint emission lines required to characterise the direct method gas-phase abundance. I will present results from deep optical IFU observations of 4 nearby HII regions in the Magellanic Clouds using the Wide-Field Spectrograph on the ANU 2.3m telescope. At the sub-parsec scales of our observations, we resolve the electron temperature, density, chemical and ionisation structure within the HII regions, and study their spatial variation with line-of-sight radial gradients. We show that density clumps and inhomogeneities present within HII regions may bias the derived electron temperature, which impacts the measured gas-phase oxygen abundance. Our results illustrate the complexity of internal structures and variety of conditions present within nebulae, and highlight the importance of adequately constraining the internal ionisation and temperature structure within HII regions when probing spatial variations of gas-phase metallicity across galaxies.

This contribution can be found in the Poster Hall.