Results of the ESO-SEST Key Programme on CO in the Magellanic Clouds - IX - The giant LMC HII region complex N 11

Abstract

The second-brightest star formation complex in the Large Magellanic Cloud, N 11, was surveyed extensively in the J = 1–0 transition of 12CO. In this paper we present maps and a catalogue containing the parameters of 29 individual molecular clouds in the complex, although more may be present. The distribution of molecular gas in the N 11 complex is highly structured. In the southwestern part of N 11, molecular clouds occur in a ring or shell surrounding the major OB star association LH 9. In the northeastern part, a chain of molecular clouds delineates the rim of one of the so-called supergiant shells in the LMC. There appears to be very little diffuse molecular gas in-between the individual well-defined clouds, especially in the southwestern ring. Most of the clouds have dimensions only slightly larger than those of the survey beam, i.e. diameters of 25 pc or less. A subset of the clouds mapped in J = 1–012CO transition was also observed in the J = 2–1 12CO transition, and in the corresponding transitions of 13CO. Clouds mapped in J = 2–1 12CO with a two times higher angular resolution show further, clear substructure. The elements of this substructure, however, have dimensions once again comparable to those of the mapping beam. For a few clouds, sufficient information was available to warrant an attempt at modelling their physical parameters. They contain fairly warm (Tkin = 60–150 K) and moderately dense (nH2 = 3000 cm−3) gas. The northeastern chain of CO clouds, although lacking in diffuse intercloud emission, is characteristic of the more quiescent regions of the LMC, and appears to have been subject to relatively little photo-processing. The clouds forming part of the southwestern shell or ring, however, are almost devoid of diffuse intercloud emission, and also exhibit other characteristics of an extreme photon-dominated region (PDR).