Twisting magnetic fields in the core region of OMC-1

We present results of imaging polarimetry of the | H₂ v=1-0| S (1) line in the core region of OMC-1. The polarization vectors are produced by dichroic absorption in a medium of aligned grains and therefore follow the direction of the magnetic field in the region. The magnetic field strength estimated from the dispersion of polarization vectors is |10 \ mG|⁠, which is sufficient to align the grains via the Davis–Greenstein mechanism. The presence of a twist in the direction of the magnetic field about the self-luminous object IRc2 is clearly seen. We propose a model which requires the magnetic field to be poloidal outside the disc of IRc2, but which develops a significant transverse component close to the disc.