How Does Metallicity Affect the Gas and Dust Properties of Galaxies?

TL;DR

This study compares the interstellar medium of metal-poor and metal-rich galaxies, revealing that low metallicity leads to higher dust temperatures, more porous ISM, and significant CO-dark molecular gas, affecting galaxy evolution understanding.

Contribution

It provides detailed modeling of low-metallicity ISM, highlighting the prevalence of CO-dark H2 and the importance of combined gas and dust diagnostics for galaxy analysis.

Findings

Low-metallicity galaxies have higher dust temperatures.

Porous ISM allows deeper photodissociation of molecular clouds.

Significant CO-dark H2 reservoirs are present in dwarf galaxies.

Abstract

Comparison of the ISM properties of a wide range of metal-poor galaxies with normal metal-rich galaxies reveals striking differences. We find that the combination of the low dust abundance and the active star formation results in a very porous ISM filled with hard photons, heating the dust in dwarf galaxies to overall higher temperatures than their metal-rich counterparts. This results in photodissociation of molecular clouds to greater depths, leaving relatively large PDR envelopes and difficult-to-detect CO cores. From detailed modeling of the low-metallicity ISM, we find significant fractions of CO-dark H2 - a reservoir of molecular gas not traced by CO, but present in the [CII] and [CI]-emitting envelopes. Self-consistent analyses of the neutral and ionized gas diagnostics along with the dust SED is the necessary way forward in uncovering the multiphase structure of galaxies