C-II REGION COMPLEXES N159 AND N160( EMISSION FROM THE MAGELLANIC CLOUDS .1. THE BRIGHT H)

We have mapped the [C II] 158 mu m line toward the bright Large Magell anic Cloud H II regions N160 and N159. Both H II region/molecular clou d complexes are associated with extended clouds of C+. Comparison with CO observations of similar resolution shows that in both complexes pe ak 158 mu m emission occurs at the interfaces of the H II region and t he associated molecular clouds, while more diffuse extended 158 mu m e mission covers the entire molecular cloud complexes. Including the res ults on 30 Dor published elsewhere, the ratio of [C II] to CO intensit ies differs from cloud to cloud over 3 orders of magnitude, presumably reflecting evolutionary differences in cloud structure. The ratio of 158 mu m to far-infrared intensities also shows some variation, but ov er a much smaller range. It is typically around 1% and considerably hi gher than in Galactic clouds and in most galactic nuclei. Thus, at lea st on spatial scales of tens of parsecs, the intensity of 158 mu m emi ssion correlates reasonably well, but not perfectly, with the infrared continuum intensity and very poorly with the CO intensity. The observ ed 158 mu m emission appears to be optically thin, implying minimum co lumn densities N-H(min) = 3 x 10(21) cm(-2). In contrast to Galactic o bjects, in three of the four clouds observed, the total mass of the ph oton-dominated region (PDR) is a significant fraction of the total com plex mass, although not to the extreme extent deduced for 30 Dor. The relative morphologies of [C II], CO, and far-infrared emission, as wel l as derived properties such as the high PDR-to-molecular mass ratios and the high photoelectric heating efficiencies characterizing the obs erved clouds, can be understood as the result of the lower metallicity and lower dust-to-gas ratio in the Large Magellanic Cloud relative to those in the Galaxy. This causes the cloud volume in which CO is abun dant to shrink while simultaneously increasing the PDR volume; in addi tion, it produces a lower mean UV radiation field in the PDR zone by i ncreasing the UV photon mean free path lengths, resulting in greater g eometric dilution of the radiation held.