Interferometric mapping of magnetic fields in star-forming regions. II. NGC 2024 FIR 5

We present the first interferometric polarization maps of the NGC 2024 FIR 5 molecular core, obtained with the BIMA array at approximately 2 resolution. We measure an average position angle of -60degrees +/- 6degrees in the main core of FIR 5 and 54degrees +/- 9degrees in the eastern wing of FIR 5. The morphology of the polarization angles in the main core of FIR 5 suggests that the field lines are parabolic, with a symmetry axis approximately parallel to the major axis of the putative disk in FIR 5, which is consistent with the theoretical scenario that the gravitational collapse pulled the field lines into an hourglass shape. The polarization percentage decreases toward regions with high intensity and close to the center of the core, suggesting that the dust alignment efficiency may decrease at high density. The plane-of-sky field strength can be estimated with the modified Chandrasekhar-Fermi formula, and the small dispersion of the polarization angles in FIR 5 suggests that the magnetic field is strong (greater than or similar to2 mG) and perhaps dominates the turbulent motions in the core.