THE LIFE AND DEATH OF DENSE MOLECULAR CLUMPS IN THE LARGE MAGELLANIC CLOUD

We report the results of a high spatial (parsec) resolution HCO+ (J = 1 -> 0) and HCN (J = 1 -> 0) emission survey toward the giant molecular clouds of the star formation regions N 105, N 113, N 159, and N 44 in the Large Magellanic Cloud (LMC). The HCO+ and HCN observations at 89.2 and 88.6 GHz, respectively, were conducted in the compact configuration of the Australia Telescope Compact Array. The emission is imaged into individual clumps with masses between 10(2) and 10(4) M-circle dot and radii of < 1 pc to similar to 2 pc. Many of the clumps are coincident with indicators of current massive star formation, indicating that many of the clumps are associated with deeply embedded forming stars and star clusters. We find that massive young stellar object (YSO) bearing clumps tend to be larger (greater than or similar to 1 pc), more massive (M greater than or similar to 10(3)M(circle dot)), and have higher surface densities (similar to 1 g cm(-2)), while clumps without signs of star formation are smaller (less than or similar to 1 pc), less massive (M less than or similar to 10(3) M-circle dot), and have lower surface densities (similar to 0.1 g cm(-2)). The dearth of massive (M > 10(3) M-circle dot) clumps not bearing massive YSOs suggests that the onset of star formation occurs rapidly once the clump has attained physical properties favorable to massive star formation. Using a large sample of LMC massive YSO mid-IR spectra, we estimate that similar to 2/3 of the massive YSOs for which there are Spitzer mid-IR spectra are no longer located in molecular clumps; we estimate that these young stars/clusters have destroyed their natal clumps on a timescale of at least similar to 3 x 10(5) yr.