%0 Journal Article %T Magnetic Fields in Star-Forming Molecular Clouds I. The First Polarimetry of OMC-3 in Orion A %A Brenda C. Matthews %A Christine D. Wilson %J Physics %D 1999 %I arXiv %R 10.1086/308523 %X The first polarimetric images of the OMC-3 region of the Orion A filamentary molecular cloud are presented. Using the JCMT, we have detected polarized thermal emission at 850 microns from dust along a 6' length of the dense filament. The polarization pattern is highly ordered and is aligned with the filament throughout most of the region. The plane-of-sky magnetic field direction is perpendicular to the measured polarization. The mean percentage polarization is 4.2% with a 1 sigma dispersion of 1%. This region is part of the integral-shaped filament, and active star formation is ongoing along its length. The protostellar outflow directions do not appear to be consistently correlated with the direction of the plane-of-sky field or the filament structure itself. Depolarization toward the filament center, previously detected in many other star-forming cores and protostars, is also evident in our data. (abstract abridged) %U http://arxiv.org/abs/astro-ph/9911148v1