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Session 6 - The ISM & Molecular Clouds.
Display session, Monday, June 09
South Main Hall,
We have carried out VLA Zeeman observations of \ion H1 absorption lines toward the \ion H2 region in the M17 giant molecular cloud complex. The resulting maps have 45\arcsec\/\times60\arcsec\/ spatial resolution and 0.64 kms^-1 velocity resolution. M17 provides a unique opportunity to investigate the interaction of an \ion H2 region-molecular cloud interface due its edge-on geometry. The \ion H1 absorption lines toward M17 show between 5 and 8 distinct velocity components. We explore possible physical connections between these components and the M17 region based on calculations of \ion H1 column densities, line of sight magnetic field strengths, as well as comparisons with a wide array of previous optical, infrared, and radio observations. These analyses have led us to adopt a model in which at least two of these \ion H1 components originate from \ion H1 gas in the PDR which has formed at the southwestern \ion H2 region-molecular cloud boundary.
In particular, a component at the same velocity as the M17 molecular cloud \sim20 kms^-1 seems to originate from the edge-on interface between the \ion H2 region and molecular cloud in the southwestern part of the source. For this component we have detected a steep peaking up of both the \ion H1 column density divided by spin temperature (\geq5.6\times10^19 cm^-2\//K) and line of sight magnetic field strengths (\B_los\/ \sim-450 \muG\/) toward this boundary. In addition, we believe that the blended component at velocities between 12 to 16 kms^-1 originates from the front side of the PDR which has formed between the \ion H2 region and a lip of molecular gas which is believed to have curved around like a bowl to obscure the Southern bar of the \ion H2 region. The peak \ion H1 column density divided by spin temperature and \B_los\/ for this component is \geq4.4\times10^19 cm^-2\//K and \sim550 \muG\/ respectively. Magnetic field detections were also made at 4, 6, and 25 kms^-1.
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