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K. E. Kraemer (Boston University)
The far-ultraviolet (FUV) radiation of massive stars dominates the heating of the interstellar medium (ISM). The gas within the photodissociation regions (PDR), which this FUV radiation creates, dominates the cooling of the gaseous ISM. The goal of this thesis is to determine how the properties of the PDR and molecular gas are affected by the FUV fields of newly formed massive stars. NGC 6334, a nearby molecular cloud with several sites of massive star formation, was observed with airborne and ground-based telescopes in ionized carbon and neutral oxygen ([C II] 158 \mum, [O I] 145 \mum, and [O I] 63 \mum) and in several molecular (CO, CS, and NH3) transitions. These observations were compared to theoretical PDR models to test the models' validity.
The extended [C II] 158 \mum emission in NGC 6334 indicates that the gas distribution is clumpy. The [O I] 63 \mum line was observed for the first time in absorption against a continuum source. It was also fainter than predicted toward three other sources in the cloud. The [O I] 63 \mum transition is probably self-absorbed by cooler foreground material, an effect not accounted for in the current PDR models. Until the models include the radiative transfer through the molecular cloud, the use of the [O I] 63 \mum line as a PDR diagnostic is problematic at best.
The molecular emission in NGC 6334 shows a complex structure of filaments and bubbles, some of which are filled with PDR gas. The dense gas is anticorrelated with the 6 cm radio flux. The hottest stars have destroyed the remnants of the dense molecular gas from which they formed, while the other, cooler stars may not have hard enough radiation to dissociate the molecules, or have not had time to disperse the dense molecular gas. The CO data suggest temperatures (T~0 K) and column densities (N\rm H_2~ 1022~\rm cm-2) typical of those found in the warm molecular cores of other sites of massive star formation.
Finally, the properties of the individual sources are examined and a description of how each source fits into the broad scheme of massive star formation is presented.
The author(s) of this abstract have provided an email address for comments about the abstract: kraemer@protostar.bu.edu