Metal Mixing and Ejection in Dwarf Galaxies is Dependent on Nucleosynthetic Source

TL;DR

This study uses high-resolution simulations to analyze how different metal sources affect their distribution and ejection in dwarf galaxies, revealing distinct mixing behaviors and retention rates based on nucleosynthetic origin.

Contribution

It demonstrates for the first time that metal species in dwarf galaxies follow specific distribution patterns and that AGB-synthesized elements are less efficiently mixed and retained than supernova-synthesized elements.

Findings

Metal PDFs are well described by piecewise log-normal and power-law functions.

AGB elements like N and Ba mix less efficiently than supernova elements.

Over 20% of AGB-synthesized metals are retained in the galaxy.

Abstract

Using a high resolution simulation of an isolated dwarf galaxy, accounting for multi-channel stellar feedback and chemical evolution on a star-by-star basis, we investigate how each of 15 metal species are distributed within our multi-phase interstellar medium (ISM) and ejected from our galaxy by galactic winds. For the first time, we demonstrate that the mass fraction probability distribution functions (PDFs) of individual metal species in the ISM are well described by a piecewise log-normal and power-law distribution. The PDF properties vary within each ISM phase. Hot gas is dominated by recent enrichment, with a significant power-law tail to high metal fractions, while cold gas is predominately log-normal. In addition, elements dominated by asymptotic giant branch (AGB) wind enrichment (e.g. N and Ba) mix less efficiently than elements dominated by supernova enrichment (e.g. $\alpha$ elements and Fe). This result is driven by the differences in source energetics and source locations, particularly the higher chance compared to massive stars for AGB stars to eject material into cold gas. Nearly all of the produced metals are ejected from the galaxy (only 4% are retained), but over 20% of metals dominated by AGB enrichment are retained. In dwarf galaxies, therefore, elements synthesized predominately through AGB winds should be both overabundant and have a larger spread compared to elements synthesized in either core collapse or Type Ia supernovae. We discuss the observational implications of these results, their potential use in developing improved models of galactic chemical evolution, and their generalization to more massive galaxies.