Multi-colour imaging polarimetry of the galaxy NGC 2146

Imaging polarimetry data in BVRI wavebands are presented for the bright infrared galaxy NGC 2146. The optical appearance of this galaxy is dominated by a distinctive central dust lane and in this region we find significant levels of polarization orientated parallel to the plane of the dust lane. We believe that the dust lane polarization is produced by dichroic extinction by magnetically aligned dust grains, which implies that the magnetic field is uniform on kpc scale lengths. In the areas not obscured by the dust lane, the polarization pattern is typical of a huge galactic-scale reflection nebula illuminated predominantly by a source hidden from our direct view and located behind the densest part of the dust lane. We discuss the nature of this source in terms of a starburst and/or an AGN. NGC 2146 has similar polarization properties to other starburst galaxies such as M82 and NGC 1808.