ASTE observations in the 345 GHz window towards the HII region N113 of the Large Magellanic Cloud

Abstract

Aims. The HII region N113 is located in the central part of the Large Magellanic Cloud (LMC) with an associated molecular cloud that is very rich in molecular species. Most of the previously observed molecular lines cover the frequency range 85–270 GHz. Thus, a survey and study of lines at the 345 GHz window is required for a more complete understanding of the chemistry and excitation conditions of this region. Methods. We mapped a region of 2.́5 × 2.́5 centred at N113 using the Atacama Submillimeter Telescope Experiment in the 13CO J = 3−2 line with an angular and spectral resolution of 22′′ and 0.11 km s-1. In addition, we observed 16 molecular lines as single pointings towards its centre. Results. From the 13CO J = 3−2 map we estimate the local thermodynamic equilibrium (LTE) and virial masses in about 1 × 104 and 4.5 × 104M⊙ for the molecular cloud associated with N113. From the dust continuum emission at 500 μm we additionally obtain a mass of gas of 7 × 103M⊙. Towards the cloud centre we detected emission from 12CO, 13CO, C18O (3–2), HCN, HNC, HCO+, C2H (4–3), and CS (7–6); these are the first reported detections of the HCN, HNC, and C2H (4–3) lines from this region. We confirm the detection of CS (7–6), which was previously tentatively detected. From analysing the HCN, HNC, and C2H lines we suggest that they might be emitted from a photodissociation region (PDR). Moreover, we suggest that the chemistry involving the C2H lines in N113 is probably similar to that in Galactic PDRs. We analysed the HCN J = 4−3, J = 3−2, and J = 1−0 lines with the code RADEX and we conclude that we observe very high density gas, between some 105 and 107 cm-3.