Infrared polarimetry of galaxies. III. Global comparisons

Many infrared-luminous (L_FIR) ≥ 10¹² L_⊙) and/or starburst galaxies show simple interstellar polarization in the infrared, but the magnitude of the polarization is significantly lower than expected for the observed near-infrared color excess. Possible explanations, including a scrambled magnetic field, dilution from hot dust emission, and a "crossed polaroid" geometry are discussed. Only the model with a polar nuclear field at right angles to a planar disk field, causing a "crossed polaroid" effect, is consistent with other observations of these galaxies. This suggests that most infrared-luminous and starburst galaxies have massive polar outflows from their nuclei.