Pumping Iron: How turbulent metal diffusion impacts multiphase galactic outflows

TL;DR

This study examines how turbulent metal diffusion models influence multiphase galactic outflows in dwarf galaxies, revealing that metal diffusion affects cooling rates and metal distribution but only weakly impacts overall mass, energy, and metal loading factors.

Contribution

The paper introduces a high-resolution simulation approach to assess the effects of turbulent metal diffusion on galactic outflows, highlighting its impact on cooling and metal enrichment in different gas phases.

Findings

Metal diffusion increases metal enrichment at low altitudes.

Cooling is more efficient in the cold interstellar medium with metal diffusion.

Hot phase cooling is faster without metal diffusion, reducing sound speed.

Abstract

Most numerical simulations of galaxy formation and evolution are unable to properly resolve the turbulent cascade at or below the resolution scale and turbulence models are required to capture the motion of eddies on those unresolved scales. In this study, we investigate the impact of turbulent metal diffusion models on multiphase outflows originating from dwarf galaxies ($M_{\rm halo} \sim 10^{10} - 10^{11}$ M$_\odot$). We use our state-of-the-art numerical model for the formation of single stars and non-equilibrium cooling and hydrogen chemistry. Our simulations are carried out at a mass resolution of $\sim$1 M$_{\odot}$, where the individual supernova explosions are resolved in terms of hot-phase generation and momentum input. We find that mass, energy, and metal loading factors are only weakly affected by the inclusion of a metal diffusion model. The metal enrichment factor at low altitude above the galactic disk is higher by around 20 per cent when the metal diffusion model is included. Specifically, we find more efficient cooling in the cold interstellar medium, as higher amounts of metals are kept in the cold dense phase. The most striking effect of the metal diffusion model is that, without metal diffusion, there is more rapid cooling in the hot phase and a reduced sound speed by a factor of two. Specifically, we find that the hot phase is more metal enriched in the case without metal diffusion leading to more rapid (over) cooling of that phase which is consistent with the higher sound speed we find in the runs with metal diffusion.