Millimeter dust emission compared with other mass estimates in N11
  molecular clouds in the LMC
  CO and dust emission at millimeter wavelengths are independent tracers of
cold interstellar matter, which have seldom been compared on the scale of GMCs
in other galaxies. In this study, and for the first time in the Large
Magellanic Cloud, we compute the molecular cloud masses from the mm emission of
the dust and compare them with the masses derived from their CO luminosity and
virial theorem. We present CO (J=1-0,2-1) and 1.2 mm continuum observations of
the N11 star forming region in the LMC obtained with the SEST telescope and the
SIMBA bolometer, respectively. We use the CO data to identify individual
molecular clouds and measure their physical properties. The correlations
between the properties of the N11 clouds are in agreement with those found in
earlier studies in the LMC that sample a larger set of clouds and a larger
range of cloud masses. For the N11 molecular clouds, we compare the masses
estimated from the CO luminosity (Xco\Lco), the virial theorem (Mvir) and the
millimeter dust luminosity (L_d). The measured ratios Lco/Mvir and L_d/Mvir
constrain the Xco and K_d (dust emissivity at 1.2 mm per unit gas mass)
parameters as a function of the virial parameter a_vir. The comparison between
the different mass estimates yields a Xco-factor of 8.8x10^20 cm-2/(K km s-1) x
a_vir and a K_d parameter of 1.5x10^-3 cm2/g x a_vir. We compare our N11
results with a similar analysis for molecular clouds in the Gould's Belt. We do
not find in N11 a large discrepancy between the dust mm and virial masses as
reported in earlier studies of molecular clouds in the SMC. The ratio between
L_d and Mvir in N11 is half of that measured for Gould's Belt clouds, which can
be accounted for by a factor of two lower gas-to-dust mass ratio, as the
difference in gas metallicities. If the two samples have similar a_vir values,
this result implies that their dust far-IR properties are also similar.
