FIRST DETECTION OF AMMONIA IN THE LARGE MAGELLANIC CLOUD: THE KINETIC TEMPERATURE OF DENSE MOLECULAR CORES IN N 159 W

The first detection of ammonia (NH3) is reported from the Magellanic Clouds. Using the Australia Telescope Compact Array, we present a targeted search for the (J,K) = ( 1,1) and ( 2,2) inversion lines toward seven prominent star-forming regions in the Large Magellanic Cloud (LMC). Both lines are detected in the massive star-forming region N 159 W, which is located in the peculiar molecular ridge south of 30 Doradus, a site of extreme star formation strongly influenced by an interaction with the Milky Way halo. Using the ammonia lines, we derive a kinetic temperature of similar to 16 K, which is 2-3 times below the previously derived dust temperature. The ammonia column density, averaged over similar to 17 '', is similar to 6 x 10(12) cm(-2) (<1.5 x 10(13) cm(-2) over 9 '' in the other six sources) and we derive an ammonia abundance of similar to 4 x 10(-10) with respect to molecular hydrogen. This fractional abundance is 1.5-5 orders of magnitude below those observed in Galactic star-forming regions. The nitrogen abundance in the LMC (similar to 10% solar) and the high UV flux, which can photo-dissociate the particularly fragile NH3 molecule, both must contribute to the low fractional NH3 abundance, and we likely only see the molecule in an ensemble of the densest, best shielded cores of the LMC.