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 ASTE we mapped a 2 \aas@@fstack { \prime } 4 \times 2 \aas@@fstack { \prime } 4 region towards the molecular cloud N159-W in the ^ { 13 } CO J=3–2 line and observed several molecular lines at an IR peak very close to a massive young stellar object . ^ { 12 } CO and ^ { 13 } CO J=3–2 were observed towards two positions in N166 and one position in N132 .
The ^ { 13 } CO J=3–2 map of the N159-W cloud shows that the molecular peak is shifted southwest compared to the peak of the IR emission .
Towards the IR peak we detected emission from HCN , HNC , HCO ^ { + } , C _ { 2 } H J=4–3 , CS J=7–6 , and tentatively C ^ { 18 } O J=3–2 .
This is the first reported detection of these molecular lines in N159-W .
The analysis of the C _ { 2 } H line yields more evidence supporting that the chemistry involving this molecular species in compact and/or UCH ii regions in the LMC should be similar to that in Galactic ones .
A non-LTE 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 \times 10 ^ { 5 } to some 10 ^ { 6 } cm ^ { -3 } .
The obtained \frac { 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 10 ^ { 3 } cm ^ { -3 } .