Special Colloquium - "Magnetic Fields in PDRs - Zeeman Effect Measurements and Their Implications"
(sign-up)Tom Troland, University of Kentucky
Prof. Richard Crutcher
Aperture synthesis observations of the 21cm HI Zeeman effect offer an unusual opportunity to measure magnetic field strengths in PDRs. If a PDR lies in front of an H+ region, strong radio free-free emission can create deep HI absorption lines that are very sensitive to the Zeeman effect. Zeeman observations have been performed toward a number of galactic H+ regions. PDR field strengths are often quite high (up to a milligauss). Published Cloudy PDR models of M17 describe an equilibrium between magnetic pressure and the momentum of absorbed stellar uv radiation. This model can be applied to all H+ regions for which Zeeman measurements exist. The model suggests that magnetic fields play a crucial role in determining PDR physical properties such as depth and density.
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