The Relationship Between Molecular Gas, HI, and Star Formation in the Low-Mass, Low-Metallicity Magellanic Clouds

TL;DR

This study investigates how molecular gas, atomic hydrogen, and star formation relate in the low-metallicity Magellanic Clouds using dust emission data, revealing insights into gas depletion times and the influence of metallicity.

Contribution

The paper introduces a dust-based method to map molecular gas in the Magellanic Clouds, avoiding CO biases, and compares observed star formation models across different metallicities.

Findings

Molecular gas depletion times are ~0.4 Gyr in LMC and ~0.6 Gyr in SMC.

No strong dependence of depletion time on metallicity was observed.

Both star formation models predict the observed trends, emphasizing the role of diffuse neutral medium.

Abstract

The Magellanic Clouds provide the only laboratory to study the effect of metallicity and galaxy mass on molecular gas and star formation at high (~20 pc) resolution. We use the dust emission from HERITAGE Herschel data to map the molecular gas in the Magellanic Clouds, avoiding the known biases of CO emission as a tracer of H$_{2}$. Using our dust-based molecular gas estimates, we find molecular gas depletion times of ~0.4 Gyr in the LMC and ~0.6 SMC at 1 kpc scales. These depletion times fall within the range found for normal disk galaxies, but are shorter than the average value, which could be due to recent bursts in star formation. We find no evidence for a strong intrinsic dependence of the molecular gas depletion time on metallicity. We study the relationship between gas and star formation rate across a range in size scales from 20 pc to ~1 kpc, including how the scatter in molecular gas depletion time changes with size scale, and discuss the physical mechanisms driving the relationships. We compare the metallicity-dependent star formation models of Ostriker, McKee, and Leroy (2010) and Krumholz (2013) to our observations and find that they both predict the trend in the data, suggesting that the inclusion of a diffuse neutral medium is important at lower metallicity.