First Results of a CO Survey of the Large Magellanic Cloud with NANTEN; Giant Molecular Clouds as Formation Sites of Populous Clusters

A new survey of the LMC has been completed in 2.6 mm carbon monoxide emission with NANTEN. This survey has revealed 107 giant molecular clouds, the first complete sample of giant molecular clouds in a single galaxy at a linear resolution of ~ 40 pc. The cloud mass ranges from ~ 6 x 10⁴ to 2 x 10⁶ M_sun, and the total molecular mass has been estimated to be 4-7 x 10⁷ M_sun for a molecular column density of >~ 1.0 x 10²¹ cm^-2, corresponding to 5-10% of the atomic mass. The molecular clouds exhibit a good spatial correlation with the youngest stellar clusters whose ages are <~ 10 Myr, demonstrating that cluster formation is on-going in these clouds. On the other hand, they show little correlation with older clusters or with supernova remnants, suggesting that the molecular clouds are being rapidly dissipated in a several Myrs, probably due to the UV photons of massive stars in clusters.