2014A&A...572A..56P

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 85-270GHz. Thus, a survey and study of lines at the 345GHz window is required for a more complete understanding of the chemistry and excitation conditions of this region. We mapped a region of 2.5'x2.5' 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 0.11km/s. In addition, we observed 16 molecular lines as single pointings towards its centre. From the ¹³CO J=3-2 map we estimate the local thermodynamic equilibrium (LTE) and virial masses in about 1x10⁴ and 4.5x10⁴M_☉ for the molecular cloud associated with N113. From the dust continuum emission at 500µm we additionally obtain a mass of gas of 7x10³M_☉. 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 10⁷cm^–3.