The Chemical Evolution Carousel of Spiral Galaxies: Azimuthal Variations of Oxygen Abundance in NGC1365

TL;DR

This study reveals azimuthal variations in oxygen abundance in NGC1365, driven by localized enrichment and spiral wave-induced mixing, highlighting complex chemical evolution processes in spiral galaxies.

Contribution

It provides the first detailed case study linking azimuthal oxygen abundance variations to physical processes like enrichment and mixing in a spiral galaxy.

Findings

Azimuthal oxygen variations of 0.2 dex observed.

Variations occur over 0.3 to 0.7 R25 radial range.

A simple model reproduces the observed abundance patterns.

Abstract

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.