2016MNRAS.455..518P

We present results obtained towards the HII regions N159, N166, and N132 from the emission of several molecular lines in the 345 GHz window. Using Atacama Submillimetre Telescope Experiment, we mapped a 2.4 arcminx2.4 arcmin region towards the molecular cloud N159-W in the 13CO J = 3-2 line and observed several molecular lines at an infrared (IR) peak very close to a massive young stellar object. 12CO and 13CO J = 3-2 were observed towards two positions in N166 and one position in N132. The 13CO J = 3-2 map of the N159-W cloud shows that the molecular peak is shifted south-west compared to the peak of the IR emission. Towards the IR peak, we detected emission from HCN, HNC, HCO+, C2H J = 4-3, CS J = 7-6, and tentatively C18O J = 3-2. This is the first reported detection of these molecular lines in N159-W. The analysis of the C2H line yields more evidence supporting that the chemistry involving this molecular species in compact and/or UC HII regions in the Large Magellanic Cloud should be similar to that in Galactic ones. A non-LTE (local thermodynamic equilibrium) study of the CO emission suggests the presence of both cool and warm gas in the analysed region. The same analysis for the CS, HCO+, HCN, and HNC shows that it is very likely that their emissions arise mainly from warm gas with a density between 5x10⁵ to some 10⁶/ cm3. The obtained HCN/HNC abundance ratio greater than 1 is compatible with warm gas and with an star-forming scenario. From the analysis of the molecular lines observed towards N132 and N166, we propose that both regions should have similar physical conditions, with densities of about 10³/ cm3.