A view of Large Magellanic Cloud H ii regions N159, N132, and N166 through the 345-GHz window

Abstract

We present results obtained towards the H II 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 arcmin × 2.4 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 H II 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 5 × 105 to some 106 cm−3. 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 cm−3.