Metal diffusion in smoothed particle hydrodynamics simulations of dwarf galaxies

TL;DR

This study uses smoothed particle hydrodynamics simulations to explore how different metal diffusion models affect the chemical evolution and outflows in dwarf galaxies, revealing that diffusion strength influences gas metallicity and outflow efficiency.

Contribution

It systematically compares various metal diffusion models in dwarf galaxy simulations, highlighting their impact on metallicity distributions and outflow properties.

Findings

Stronger diffusion tightens the gas [O/Fe]-[Fe/H] distribution.

Diffusion suppresses low-metallicity star formation.

Metal outflows are strongly affected by diffusion strength.

Abstract

We perform a series of smoothed particle hydrodynamics simulations of isolated dwarf galaxies to compare different metal mixing models. In particular, we examine the role of diffusion in the production of enriched outflows, and in determining the metallicity distributions of gas and stars. We investigate different diffusion strengths, by changing the pre-factor of the diffusion coefficient, by varying how the diffusion coefficient is calculated from the local velocity distribution, and by varying whether the speed of sound is included as a velocity term. Stronger diffusion produces a tighter [O/Fe]-[Fe/H] distribution in the gas, and cuts off the gas metallicity distribution function at lower metallicities. Diffusion suppresses the formation of low-metallicity stars, even with weak diffusion, and also strips metals from enriched outflows. This produces a remarkably tight correlation between "metal mass-loading" (mean metal outflow rate divided by mean metal production rate) and the strength of diffusion, even when the diffusion coefficient is calculated in different ways. The effectiveness of outflows at removing metals from dwarf galaxies and the metal distribution of the gas is thus dependent on the strength of diffusion. By contrast, we show that the metallicities of stars are not strongly dependent on the strength of diffusion, provided that some diffusion is present.