Astronomy and Astrophysics, volume 465, 887-898 (2007/4-3)
The interaction of young massive stars with their environment. A millimeter and submillimeter line study of NGC 6334 FIRII.
ZHANG J.S., HENKEL C., MAUERSBERGER R., CHIN Y.-N., MENTEN K.M., TIEFTRUNK A.R. and BELLOCHE A.
Abstract (from CDS):
Using the 15-m Swedish ESO Sub-millimeter Telescope (SEST), CO, HCN, and HCO+ observations of the galactic star-forming region NGC6334FIRII are presented, complemented by [CI] 3P1-3P0 and 3P2-3P1 data from the Atacama Pathfinder Experiment (APEX 12-m telescope). Embedded in the extended molecular cloud and associated with the Hii region NGC6334-D, there is a molecular ``void''. [CI] correlates well with 13CO and other molecular lines and shows no rim brightening relative to molecular cloud regions farther off the void. While an interpretation in terms of a highly clumped cloud morphology is possible, with photon dominated regions (PDRs) reaching deep into the cloud, the data do not provide any direct evidence for a close association of [CI] with PDRs. Kinetic temperatures are ∼40-50K in the molecular cloud and >200K toward the void. CO and [CI] excitation temperatures are similar. A comparison of molecular and atomic fine structure line emission with the far infrared and radio continuum as well as the distribution of 2.2µm H2 emission indicates that the well-evolved Hii region expands into a medium that is homogeneous on pc-scales. If the H2 emission is predominantly shock excited, both the expanding ionization front (classified as subsonic, ``D-type'') and the associated shock front farther out (traced by H2) can be identified, observationally confirming for the first time a classical scenario that is predicted by evolutionary models of Hii regions. Integrated line intensity ratios of the observed molecules are determined, implying a mean C18O/C17O abundance ratio of 4.13±0.13 that reflects the 18O/17O isotope ratio. This ratio is consistent with values determined in nearby clouds. Right at the edge of the void, however, the oxygen isotope ratio might be smaller.
ISM: abundances - ISM: atoms - ISM: HII regions - ISM: individual objects: NGC6334 FIRII - ISM: molecules - radio lines: ISM
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