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

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.

24 pages, 14 figures, accepted for publication in ApJ. FITS files of the dust-based estimates of the H2 column densities for the LMC and SMC (shown in Figures 2 and 3) will be available online through ApJ

References in corpus (14)

• Infrared Emission from Interstellar Dust. IV. The Silicate-Graphite-PAH Model in the Post-Spitzer Era
• A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
• The Resolved Properties of Extragalactic Giant Molecular Clouds
• COLD GASS, an IRAM Legacy Survey of Molecular Gas in Massive Galaxies: II. The non-universality of the Molecular Gas Depletion Timescale
• The Spitzer Survey of the Small Magellanic Cloud: FIR Emission and Cold Gas in the SMC
• Dust and Gas in the Magellanic Clouds from the HERITAGE Herschel Key Project. I. Dust Properties and Insights into the Origin of the Submm Excess Emission
• Dust and Gas in the Magellanic Clouds from the HERITAGE Herschel Key Project. II. Gas-to-Dust Ratio Variations across ISM Phases
• The Structure of a Low-Metallicity Giant Molecular Cloud Complex
• Optically thick HI dominant in the local interstellar medium; an alternative interpretation to "dark gas"
• The spatially resolved Kennicutt-Schmidt relation in the HI dominated regions of spiral and dwarf irregular galaxies
• How Universal is the SFR - H2 Relation?
• The total mass and dark halo properties of the Small Magellanic Cloud
• Star-formation rates from young-star counts and the structure of the ISM across the NGC346/N66 complex in the SMC
• The Relationship between CO Emission and Visual Extinction Traced by Dust Emission in the Magellanic Clouds

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