We report the results of a high spatial ( parsec ) resolution HCO ^ { + } ( J = 1 \to 0 ) and HCN ( J = 1 \to 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 .
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 _ { \sun } and radii of < 1 pc to \sim 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 YSO-bearing clumps tend to be larger ( \gtrsim 1 pc ) , more massive ( M \gtrsim 10 ^ { 3 } M _ { \sun } ) , and have higher surface densities ( \sim 1 g cm ^ { -2 } ) , while clumps without signs of star formation are smaller ( \lesssim 1 pc ) , less massive ( M \lesssim 10 ^ { 3 } M _ { \sun } ) , and have lower surface densities ( \sim 0.1 g cm ^ { -2 } ) .
The dearth of massive ( M > 10 ^ { 3 } M _ { \sun } ) clumps not bearing massive YSOs suggests 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 \sim 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 time scale of at least \sim 3 \times 10 ^ { 5 } yrs .