The Influence of Far-Ultraviolet Radiation on the Properties of
  Molecular Clouds in the 30 Dor Region of the Large Magellanic Cloud
  We present a complete 12CO J = 1-0 map of the prominent molecular ridge in
the Large Magellanic Cloud (LMC) obtained with the 22-m ATNF Mopra Telescope.
The region stretches southward by ~2 degrees, (or 1.7kpc) from 30 Doradus, the
most vigorous star-forming region in the Local Group. The location of this
molecular ridge is unique insofar as it allows us to study the properties of
molecular gas as a function of the ambient radiation field in a low-metallicity
environment. We find that the physical properties of CO-emitting clumps within
the molecular ridge do not vary with the strength of the far-ultraviolet (FUV)
radiation field. Since the peak CO brightness of the clumps shows no
correlation with the radiation field strength, the observed constant value for
CO-to-H_2 conversion factor along the ridge seems to require an increase in the
kinetic temperature of the molecular gas that is offset by a decrease in the
angular filling factor of the CO emission. We find that the difference between
the CO-to-H_2 conversion factor in the molecular ridge and the outer Milky Way
is smaller than has been reported by previous studies of the CO emission:
applying the same cloud identification and analysis methods to our CO
observations of the LMC molecular ridge and CO data from the outer Galaxy
survey by Dame et al. (2001), we find that the average CO-to-H_2 conversion
factor in the molecular ridge is X_CO = (3.9+/-2.5)10^20 cm^-2 (K km s^-1)^-1,
approximately twice the value that we determine for the outer Galaxy clouds.
The mass spectrum and the scaling relations between the properties of the CO
clumps in the molecular ridge are similar, but not identical, to those that
have been established for Galactic molecular clouds.
