A polarisation study of spiral galaxies
Optical polarimetry results are presented for four spiral galaxies: NGC 5194 (M51), NGC 1068, NGC 4565 and NGC 4594 (Ml04). M51 and NGC 1068 show spiral polar isation patterns which are interpreted as indicating a spiral magnetic field in each case. NGC 4565 and M104 show polar isations in their dust lanes which are parallel to their galactic planes, and which are interpreted in terms of a magnetic field in the plane of each. It is hypothesised that the observed magnetic fields may be linked to galactic shocks. A discussion of the origin of galactic magnetic fields concludes that there is no evidence which necessitates a primordial magnetic field.