Statistical study of dust properties in LMC molecular clouds
  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 telescope as part of the ``Surveying the Agents of a Galaxy's
Evolution'' (SAGE) Legacy survey as well as the IRAS data. We also work with
extinction (Av) 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 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
in and outside the clouds: equilibrium temperature, emissivity and extinction.
We also determine the luminosity of the interstellar radiation field
intercepted by the cloud, and the total IR luminosity. 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 giant molecular
clouds are the sites of star formation, which heat the dust, while the smallest
clouds are unresolved. The ratio between the IR luminosity and the cloud mass
(LDust/Mgas) does not seem to correlate with Mgas. The highest value of the
ratio we derived is 18.1 Lsol/Msol 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
LDust/Mgas.
