Mapping Metallicity Variations across Nearby Galaxy Disks

Abstract

Abstract The distribution of metals within a galaxy traces the baryon cycle and the buildup of galactic disks, but the detailed gas phase metallicity distribution remains poorly sampled. We have determined the gas phase oxygen abundances for 7138 H ii regions across the disks of eight nearby galaxies using Very Large Telescope/Multi Unit Spectroscopic Explorer (MUSE) optical integral field spectroscopy as part of the PHANGS–MUSE survey. After removing the first-order radial gradients present in each galaxy, we look at the statistics of the metallicity offset (ΔO/H) and explore azimuthal variations. Across each galaxy, we find low ( σ = 0.03–0.05 dex) scatter at any given radius, indicative of efficient mixing. We compare physical parameters for those H ii regions that are 1 σ outliers toward both enhanced and reduced abundances. Regions with enhanced abundances have high ionization parameter, higher H α luminosity, lower H α velocity dispersion, younger star clusters, and associated molecular gas clouds showing higher molecular gas densities. This indicates recent star formation has locally enriched the material. Regions with reduced abundances show increased H α velocity dispersions, suggestive of mixing introducing more pristine material. We observe subtle azimuthal variations in half of the sample, but cannot always cleanly associate this with the spiral pattern. Regions with enhanced and reduced abundances are found distributed throughout the disk, and in half of our galaxies we can identify subsections of spiral arms with clearly associated metallicity gradients. This suggests spiral arms play a role in organizing and mixing the interstellar medium.