SILCC -- IX. The multi-phase interstellar medium at low metallicity

TL;DR

This study uses magnetohydrodynamic simulations to explore how low metallicity influences the multi-phase structure, star formation, and outflows in the interstellar medium, revealing significant changes in gas phases and star formation rates.

Contribution

It provides detailed simulations of the low-metallicity ISM, incorporating complex physics to show how metallicity impacts star formation and gas phase structure.

Findings

Star formation rate decreases by over tenfold at low metallicity.

Cold gas fraction drops from 60% to 2.3% as metallicity decreases.

Volume filling fraction of warm gas increases from 20% to 80%.

Abstract

The gas-phase metallicity affects heating and cooling processes in the star-forming galactic interstellar medium (ISM) as well as ionising luminosities, wind strengths, and lifetimes of massive stars. To investigate its impact, we conduct magnetohydrodynamic simulations of the ISM using the FLASH code as part of the SILCC project. The simulations assume a gas surface density of 10 M$_\odot$ pc$^{-2}$ and span metallicities from 1/50 Z$_\odot$ to 1 Z$_\odot$. We include non-equilibrium thermo-chemistry, a space- and time-variable far-UV background and cosmic ray ionisation rate, metal-dependent stellar tracks, the formation of HII regions, stellar winds, type II supernovae, and cosmic ray injection and transport. With the metallicity decreasing over the investigated range, the star formation rate decreases by more than a factor of ten, the mass fraction of cold gas decreases from 60% to 2.3%, while the volume filling fraction of the warm gas increases from 20% to 80%. Furthermore, the fraction of H$_\mathrm{2}$ in the densest regions drops by a factor of four, and the dense ISM fragments into approximately five times fewer structures at the lowest metallicity. Outflow mass loading factors remain largely unchanged, with values close to unity, except for a significant decline at the lowest metallicity. Including the major processes that regulate ISM properties, this study highlights the strong impact of gas phase metallicity on the star-forming ISM.