Magnetic Fields in Star‐forming Molecular Clouds. I. The First Polarimetry of OMC‐3 in Orion A

The first polarimetric images of the OMC-3 region of the Orion A filamentarymolecular cloud are presented. Using the JCMT, we have detected polarizedthermal emission at 850 microns from dust along a 6' length of the densefilament. The polarization pattern is highly ordered and is aligned with thefilament throughout most of the region. The plane-of-sky magnetic fielddirection is perpendicular to the measured polarization. The mean percentagepolarization is 4.2% with a 1 sigma dispersion of 1%. This region is part ofthe integral-shaped filament, and active star formation is ongoing along itslength. The protostellar outflow directions do not appear to be consistentlycorrelated with the direction of the plane-of-sky field or the filamentstructure itself. Depolarization toward the filament center, previouslydetected in many other star-forming cores and protostars, is also evident inour data. (abstract abridged)Comment: 9 pages plus 2 figures (1 colour); accepted for publication in the March 10, 2000 issue (vol. 531 #2) of The Astrophysical Journa