LABOCA observations of giant molecular clouds in the south west region of the Small Magellanic Cloud

Abstract

The amount of molecular gas is a key for understanding the future star formation in a galaxy. Because H2 is difficult to observe directly in dense and cold clouds, tracers like CO are used. However, at low metallicities especially, CO only traces the shielded interiors of the clouds. mm dust emission can be used as a tracer to unveil the total dense gas masses. The comparison of masses deduced from the continuum SIMBA 1.2 mm emission and virial masses in a sample of giant molecular clouds (GMCs), in the SW region of the Small Magellanic Cloud (SMC), showed a discrepancy that is in need of an explanation. This study aims at better assessing possible uncertainties on the dust emission observed in the sample of GMCs from the SMC and focuses on the densest parts of the GMCs where CO is detected. New observations were obtained with the LABOCA camera on the APEX telescope. All GMCs previously observed in CO are detected and their emission at 870microns is compared to ancillary data. The different contributions to the sub-mmm emission are estimated, as well as dust properties, in order to deduce molecular cloud masses precisely. The (sub-)mm emission observed in the GMCs in the SW region of the SMC is dominated by dust emission and masses are deduced for the part of each cloud where CO is detected and compared to the virial masses. The mass discrepancy between both methods is confirmed at 870microns with the LABOCA observations: the virial masses are on average 4 times smaller than the masses of dense gas deduced from dust emission, contrary to what is observed for equivalent clouds in our Galaxy. The origin of this mass discrepancy in the SMC remains unkown. The direct interpretation of this effect is that the CO linewidth used to compute virial masses do not measure the full velocity distribution of the gas. Geometrical effects and uncertainties on the dust properties are also discussed.

12 pages, 4 figures, Accepted in A&A

References in corpus (11)

• The Resolved Properties of Extragalactic Giant Molecular Clouds
• The Large APEX Bolometer Camera LABOCA
• The Spitzer Survey of the Small Magellanic Cloud: FIR Emission and Cold Gas in the SMC
• Dynamics of Dense Cores in the Perseus Molecular Cloud
• Shattering and coagulation of dust grains in interstellar turbulence
• Molecular Gas in the Low Metallicity, Star Forming Dwarf IC 10
• The Structure of a Low-Metallicity Giant Molecular Cloud Complex
• Sub-millimeter to centimeter excess emission from the Magellanic Clouds. I. Global spectral energy distribution
• Chemical composition and mixing in giant HII regions: NGC3603, 30Doradus, and N66
• The Bolocam Galactic Plane Survey -- III. Characterizing Physical Properties of Massive Star-Forming Regions in the Gemini OB1 Molecular Cloud
• A 12CO, 13CO, and C18O Survey of Infrared Dark Clouds

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