A Statistical Study of Dust Properties in Large Magellanic Cloud Molecular Clouds

Abstract

The objective of this paper is to construct a catalog providing the dust properties and the star formation efficiency (SFE) of the molecular clouds in the Large Magellanic Cloud (LMC). We use the infrared (IR) data obtained with the Spitzer Space Telescope as part of the "Surveying the Agents of a Galaxy's Evolution" Legacy survey as well as the IRAS data. We also work with extinction (A_v) maps of the LMC. A total of 272 molecular clouds have been detected in the LMC in a previous molecular survey, accounting for 230 giant molecular clouds (GMCs) and 42 smaller clouds. We perform correlations between the IR emission/extinction and atomic and molecular gas tracers. We compare the atomic gas that surrounds the molecular cloud with the molecular gas in the cloud. Using a dust emission model, we derive the physical properties of dust inside and outside the molecular clouds, such as the equilibrium temperature, composition, emissivity, and extinction. We also determine the luminosity of the interstellar radiation field (ISRF) intercepted by the cloud and the total IR luminosity from dust emission. The ratio of the IR luminosity to the gas mass traced by CO is used as an indicator of the SFE. Statistically, we do not find any significant difference in the dust properties between the atomic and the molecular phases. In particular, we do not find evidence for a systematic decrease of the dust temperature in the molecular phase, with respect to the surrounding, presumably atomic gas. This is probably because GMCs are the sites of star formation, which heat the dust, while the smallest clouds are unresolved. The ratio between the infrared luminosity and the cloud mass (L^(Dust)_(TOT)/M_(gas)) does not seem to correlate with M_(gas). The highest value of the ratio we derived is 18.1 L_⊙ M^(–1)_⊙ in the 30 Doradus region, which is known to be the most prominent star formation region of the LMC, while the most likely value is 0.5 and is representative of quiescent clouds. We provide a prescription to associate the various stages of star formation with its L^(Dust)_(TOT)/M_(gas).

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