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

TL;DR

This study maps and analyzes molecular line emissions in the Large Magellanic Cloud's HII regions N159, N132, and N166, revealing details about their physical conditions, chemistry, and star-forming activities.

Contribution

First detection of multiple molecular lines in N159-W, providing new insights into the chemistry and physical conditions of these extragalactic star-forming regions.

Findings

Detection of HCN, HNC, HCO$^{+}$, C$_{2}$H, CS, and C$^{18}$O lines in N159-W.

Evidence of both cool and warm gas components in the regions.

Similar physical conditions inferred for N132 and N166, with densities around 10$^3$ cm$^{-3}$.

Abstract

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 ASTE we mapped a 2.4' $\times$ 2.4' 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 UCHII 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 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$^{-3}$.