Magnetic fields in galaxies as revealed by the polarization of light

Some new results on optical polarization in galaxies are reported. These results as well as some other available data indicate the presence of large-scale magnetic fields in galaxies. Spiral galaxies seen nearly edge-on show polarization of light in the dark band across the center, indicating that the large-scale magnetic fields in these galaxies are mainly parallel to the symmetry plane of each galaxy, as has also been observed in the Milky Way. In more tilted galaxies, where the spiral structure can be seen more clearly, the observed polarization effects indicate large-scale magnetic fields along the arms. Observed polarization effects also indicate the presence of ordered magnetic fields in some peculiar galaxies. In NGC 2685 the fields seem to be parallel to the helical or arc-like filaments. In NGC 3718 the dark band which might be a dust-bar through the nucleus shows strong optical polarization in the direction of the band, indicating a large-scale magnetic field in the same direction.Paper dedicated to Professor Hannes Alfvén on the occasion of his 70th birthday, 30 May, 1978.