A Characteristic Mass Scale in the Mass-Metallicity Relation of Galaxies
Abstract
We study the shape of the gas-phase mass-metallicity relation (MZR) of a combined sample of present-day dwarf and high-mass star-forming galaxies using IZI, a Bayesian formalism for measuring chemical abundances presented in a previous publication. We observe a characteristic stellar mass scale at M * ≃ 109.5 M ⊙, above which the inter-stellar medium undergoes a sharp increase in its level of chemical enrichment. In the 106-109.5 M ⊙ range the MZR follows a shallow power law (Z\propto {M}* α ) with slope α = 0.14 ± 0.08. Approaching M * ≃ 109.5 M ⊙ the MZR steepens significantly, showing a slope of α = 0.37 ± 0.08 in the {10}9.5{--}{10}10.5 {M}⊙ range, and a flattening toward a constant metallicity at higher stellar masses. This behavior is qualitatively different from results in the literature that show a single power-law MZR toward the low-mass end. We thoroughly explore systematic uncertainties in our measurement, and show that the shape of the MZR is not induced by sample selection, aperture effects, a changing N/O abundance, the adopted methodology to construct the MZR, secondary dependences on star formation activity, or diffuse ionized gas contamination, but rather on differences in the method used to measure abundances. High-resolution hydrodynamical simulations of galaxies can qualitatively reproduce our result, and suggest a transition in the ability of galaxies to retain their metals for stellar masses above this threshold. The MZR characteristic mass scale also coincides with a transition in the scale height and clumpiness of cold gas disks, and a typical gas fraction below which the efficiency of star formation feedback for driving outflows is expected to decrease sharply.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 2019
- DOI:
- 10.3847/1538-4357/ab16ec
- arXiv:
- arXiv:1904.02721
- Bibcode:
- 2019ApJ...877....6B
- Keywords:
-
- galaxies: abundances;
- galaxies: evolution;
- galaxies: fundamental parameters;
- galaxies: ISM;
- ISM: abundances;
- ISM: structure;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 24 pages, 11 figures, 4 tables, accepted for publication in ApJ