Magnetic fields in star formation regions: 1.3 millimeter continuum polarimetry

We present a nine-point lambda = 1.3 mm continuum polarization map of the i nner arcminute of the DR 21 cloud core. The polarization and position angle s are very uniform, and the inferred magnetic field (P.A. similar to 75 deg rees) is nearly orthogonal to the cloud elongation (P.A. similar to 7 degre es). Applying the virial theorem and comparing the continuum polarimetry, w e find that the magnetic field strength must be greater than a few mG to ha ve a significant impact. Turbulent gas motions are probably a more signific ant source of support against self-gravity in the cloud core than in the ma gnetic held. We also report a survey of the lambda= 1.3 mm polarization of 14 star-formi ng cloud cores ([P] = 1.6%). The lambda = 1.3 mm distribution is similar to the lambda = 100 mu m and lambda = 800 mu m polarization distributions in the literature except that the 1.3 mm distribution peaks at P < 1%. We comp ared our polarimetry of nine of the cloud cores to physical parameters deri ved from far-infrared photometry in a homogeneous fashion. Consistent with theoretical expectations, the polarizations of these cloud cores do not dep end on the lambda=1.3 mm dust optical depth, emission temperature, or emiss ivity spectral index. Although the sample is very small, it appears that th e polarization is larger on average for the cloud cores with mean densities of n(H2) > 1.5 x 10(7) cm(-3) than for those with n(H2) < 1.5 x 10(7) cm(- 3) The sky-plane projection of the magnetic held lines in the seven elongated cloud cores with 800 mu m or 1.3 mm polarization detections greater than 3 sigma appear randomly distributed with respect to the position angles of cl oud core elongations. This implies that magnetic fields do not provide subs tantial anisotropic support against self-gravity in this sample of star-for ming cloud cores. The magnetic fields in the cloud cores also appear random ly oriented with respect to the Galactic plane.