CHAOS. VII. Large-scale abundance study in M33

Due to its proximity, the spiral galaxy M33 has been the focus of numerous chemical abundance surveys to study the chemical enrichment and dispersion in abundances over large spatial scales. The CHemical Abundances Of Spirals project has observed ~100 HII regions in M33 with the Large Binocular Telescope (LBT), producing the largest homogeneous sample of electron temperatures (Te) and direct abundances in this galaxy.

Our LBT observations produce a robust oxygen abundance gradient of -0.037+/-0.007dex/kpc and indicate a relatively small (0.043+/-0.015dex) intrinsic dispersion in oxygen abundance relative to this gradient. The dispersions in N/H and N/O are similarly small, and the abundances of Ne, S, Cl, and Ar relative to O are consistent with the solar ratio as expected for {alpha}-process or {alpha}-process-dependent elements. Taken together, the ISM in M33 is chemically well-mixed and homogeneously enriched from inside out, with no evidence of significant abundance variations at a given radius in the galaxy.