Results of the SEST Key Programme: CO in the Magellanic Clouds VIII. The giant molecular complex No. 37 of the LMC

Abstract

We report observations of the CO(1!0), CO(2!1) and 13CO(1!0) line emission from the giant molecular complex No. 37 of the Large Magellanic Cloud, made with linear resolutions between 6 and 12 pc. The observations were undertaken with the Swedish-ESO Submillimetre Telescope (SEST) as part of the Key Programme: CO in the Magellanic Clouds. We nd that the CO(1!0) emission arises from six large, distinct, molecular clouds, with CO luminosities in the range 1 104 to 5 104 K km s−1 pc2 and sizes between 22 and 38 pc, and seven smaller clumps, with CO luminosities in the range between 7 102 and 2 103 K km s −1 pc2. The opacities in the CO(1!0) line at the peak position of the large clouds are remarkably smaller than those derived for Galactic molecular clouds. Relationships between line width, size and CO luminosities are discussed. The total CO luminosity of the complex determined from the SEST observations, of 1:8 105 K km s −1 pc2, is in excellent agreement with that determined from the low spatial resolution ( 140 pc) observations of Cohen et al. On the other hand, the total mass of molecular gas in the complex derived from the SEST observations, assuming that the individual clouds are virialized, is 2:4 106 M , which is a factor of 6 lower than that estimated by Cohen et al. under the same assumption. We conclude that the value of the velocity integrated CO emission to H2 column density conversion factor in the LMC determined from low angular resolution observations has been overestimated by a factor of 3. We derive a conversion factor for clouds in Complex-37 of 6 1020cm −2 K −1 km −1 s, which is similar to that for clouds in the outer Galaxy.