Mapping metallicity variations across nearby galaxy disks

TL;DR

This study maps the gas phase metallicity variations across nearby galaxy disks using integral field spectroscopy, revealing efficient mixing, localized enrichment from star formation, and subtle azimuthal variations linked to spiral arms.

Contribution

First comprehensive mapping of metallicity variations across multiple galaxy disks using VLT/MUSE data, highlighting the role of spiral arms in ISM mixing and enrichment.

Findings

Low scatter in metallicity at fixed radius indicates efficient mixing.

Regions with high metallicity are associated with recent star formation and molecular gas.

Subtle azimuthal metallicity variations suggest spiral arms influence ISM organization.

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 7,138 HII regions across the disks of eight nearby galaxies using VLT/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 (Delta O/H) and explore azimuthal variations. Across each galaxy, we find low (sigma=0.03-0.05 dex) scatter at any given radius, indicative of efficient mixing. We compare physical parameters for those HII regions that are 1 sigma outliers towards both enhanced and reduced abundances. Regions with enhanced abundances have high ionization parameter, higher Halpha luminosity, lower Halpha velocity dispersion, younger star clusters and associated molecular gas clouds show higher molecular gas densities. This indicates recent star formation has locally enriched the material. Regions with reduced abundances show increased Halpha velocity dispersions, suggestive of mixing introducing more pristine material. We observe subtle azimuthal variations in half of the sample, but can not 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 ISM.