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Session 10 - Interstellar Medium and Star Formation.
Display session, Monday, June 08
Atlas Ballroom,
Theories suggest that magnetic fields are an important parameter in molecular cloud dynamics and star formation. Dust grains are preferrentially aligned in the presence of magnetic fields with their greatest average projection orthogonal to the field lines. Hence, magnetic fields can be observed with millimeter-wave polarimetry of thermal dust continuum emission.
We present a \lambda=1.3 mm continuum polarization map of DR 21. The polarization and position angles are very uniform and the inferred magnetic field is nearly orthogonal to the cloud elongation. We place an upper limit of 5 mG on the average magnetic field strength. Turbulent gas motions are a more signficant source of support against self gravity in the cloud core than magnetic fields or thermal pressure.
We also report a polarimetry survey of 14 star-forming cloud cores. We compare the physical parameters derived from far infrared photometry of nine of these to our polarimetry. Consistent with theoretical expectations, the polarizations do not depend on the 1.3 mm optical depth, dust emission temperature, or dust emissivity spectral index. We combined our observations with 800 \mum polarimetry from the literature. The sky-plane projection of the magnetic fields lines in the seven elongated cloud cores with polarizations detections >3\sigma appear randomly distributed with respect to the position angles of the cloud core elongations. This implies that magnetic fields do not provide substantial anisotropic support against self gravity in a uniform way in this sample of cloud cores. The magnetic fields also appear randomly oriented with respect to the Galactic plane. This implies that the field lines are consistent with the random component of Galactic magnetic field.
