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