Mapping metallicity variations across nearby galaxy disks
  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.
