CO-dark gas: What fuels the star formation in low metallicity dwarf galaxies?

Abstract

While star-forming dwarf galaxies have little molecular gas traced by CO, their extreme observed [Cii]/CO(1-0) and [Oiii]/[Cii] ratios set them apart from metal-rich star-forming galaxies. The decreased dust abundance, along with their star formation activity, encourages the photodissociation of CO and the presence of relatively prominent C+ envelopes which can harbor a significant self-shielded H2 reservoir, with CO being an inaccurate proxy for the total H2 gas mass. Modeling the Dwarf Galaxy Survey allows us to quantify the mass of the CO-dark H2 gas and derive a [Cii]-to-H2 gas mass conversion factor as well as a new CO-to-H2 conversion factor as a function of metallicity.