The dust content of the most metal-poor star-forming galaxies

TL;DR

This study shows that the dust content in extremely metal-poor star-forming galaxies is primarily influenced by the density of the cold interstellar medium rather than metallicity alone, explaining observed variations.

Contribution

It introduces a semi-analytical model demonstrating how ISM density affects dust formation, challenging the assumption that dust depends solely on metallicity.

Findings

Higher ISM density leads to more efficient dust grain growth.

Differences in dust mass can be explained by ISM density variations.

Models match observed dust mass differences in metal-poor galaxies.

Abstract

Although dust content is usually assumed to depend uniquely on metallicity, recent observations of two extremely metal-poor dwarf galaxies have suggested that this may not always be true. At a similar oxygen abundance of ~ 3% Zsun, the dust-to-gas and dust-to-stellar mass ratios in SBS 0335-052 and IZw 18 differ by a factor 40-70 according to including molecular gas or excluding it. Here we investigate a possible reason for this dramatic difference through models based on a semi-analytical formulation of chemical evolution including dust. Results suggest that the greater dust mass in SBS 0335-052 is due to the more efficient grain growth allowed by the high density in the cold interstellar medium (ISM), observationally inferred to be almost 20 times higher than in IZw 18. Our models are able to explain the difference in dust masses, suggesting that efficient dust formation and dust content in galaxies, including those with the highest measured redshifts, depend sensitively on the ISM density, rather than only on metallicity.