THE SUBMILLIMETER POLARIZATION SPECTRUM OF M17.

We present 450μm polarimetric observations of theM17 molecular cloud obtained with the SHARP polarimeter at the Caltech Submillimeter Observatory. Across the observed region, themagnetic field orientation is consistent with previous submillimeter and far-infrared polarization measurements. Our observations are centered on a region of the molecular cloud that has been compressed by stellar winds from a cluster of OB stars.We have compared these new data with previous 350μm polarimetry and find an anti-correlation between the 450 and 350μm polarization magnitude ratio and the ratio of 21 cm to 450μm intensity. The polarization ratio is lower near the east end of the studied region where the cloud is exposed to stellar winds and radiation. At the west end of the region, the polarization ratio is higher. We interpret the varying polarization spectrum as evidence supporting the radiative alignment torque model for grain alignment, implying higher alignment efficiency in the region that is exposed to a higher anisotropic radiation field. [ABSTRACT FROM AUTHOR]