Simulating Metal Mixing of Both Common and Rare Enrichment Sources in a Low Mass Dwarf Galaxy

TL;DR

This study uses high-resolution simulations to explore how different energetic enrichment events distribute metals in a dwarf galaxy, revealing long mixing timescales and the importance of event frequency and energy in abundance patterns.

Contribution

It provides the first detailed analysis of metal mixing timescales from various astrophysical sources in a low-mass galaxy using hydrodynamics simulations.

Findings

Mixing timescales range from 100 Myr to 1 Gyr, increasing with event energy.

More energetic events lead to more homogeneous metal distribution.

A significant fraction of metals are ejected in galactic winds, especially from hypernovae.

Abstract

One-zone models constructed to match observed stellar abundance patterns have been used extensively to constrain the sites of nucleosynthesis with sophisticated libraries of stellar evolution and stellar yields. The metal mixing included in these models is usually highly simplified, although it is likely to be a significant driver of abundance evolution. In this work we use high-resolution hydrodynamics simulations to investigate how metals from individual enrichment events with varying source energies $E_{\rm ej}$ mix throughout the multi-phase interstellar medium (ISM) of a low-mass ($M_{\rm gas}=2\times 10^{6}$~M$_{\odot}$), low-metallicity, isolated dwarf galaxy. These events correspond to the characteristic energies of both common and exotic astrophysical sites of nucleosynthesis, including: asymptotic giant branch winds ($E_{\rm ej}\sim$10$^{46}$~erg), neutron star-neutron star mergers ($E_{\rm ej}\sim$10$^{49}$~erg), supernovae ($E_{\rm ej}\sim$10$^{51}$~erg), and hypernovae ($E_{\rm ej}\sim$10$^{52}$~erg). We find the mixing timescales for individual enrichment sources in our dwarf galaxy to be long (100~Myr--1~Gyr), with a clear trend of increasing homogeneity for the more energetic events. Given these timescales, we conclude that the spatial distribution and frequency of events are important drivers of abundance homogeneity on large scales; rare, low $E_{\rm ej}$ events should be characterized by particularly broad abundance distributions. The source energy $E_{\rm ej}$ also correlates with the fraction of metals ejected in galactic winds, ranging anywhere from 60\% at the lowest energy to 95\% for hypernovae. We conclude by examining how the radial position, local ISM density, and global star formation rate influence these results.