The Chemical Evolution Carousel of Spiral Galaxies: Azimuthal Variations
  of Oxygen Abundance in NGC1365
  The spatial distribution of oxygen in the interstellar medium of galaxies is
the key to understanding how efficiently metals that are synthesized in massive
stars can be redistributed across a galaxy. We present here a case study in the
nearby spiral galaxy NGC1365 using 3D optical data obtained in the TYPHOON
Program. We find systematic azimuthal variations of the HII region oxygen
abundance imprinted on a negative radial gradient. The 0.2 dex azimuthal
variations occur over a wide radial range of 0.3 to 0.7 R25 and peak at the two
spiral arms in NGC1365. We show that the azimuthal variations can be explained
by two physical processes: gas undergoes localized, sub-kpc scale
self-enrichment when orbiting in the inter-arm region, and experiences
efficient, kpc scale mixing-induced dilution when spiral density waves pass
through. We construct a simple chemical evolution model to quantitatively test
this picture and find that our toy model can reproduce the observations. This
result suggests that the observed abundance variations in NGC1365 are a
snapshot of the dynamical local enrichment of oxygen modulated by
spiral-driven, periodic mixing and dilution.
