Galactic Magnetic Fields

Magnetic fields are a major constituent of the interstellar medium. The strength of the Galactic magnetic field ranges from µGauss to mGauss and they exist on many scales. Various radio observing techniques were used to trace small- and large-scale magnetic fields in the Galaxy, where the spatial resolution is on sub-parsec scales. Recent large-scale radio surveys of the linearly polarized emission from the Galaxy reveal a highly structured magneto-ionic interstellar medium. Especially at low frequencies Faraday rotation effects are large and depolarization is significant. Well ordered regular magnetic fields were detected in low density regions by Faraday rotating polarized background emission. The nature of these Faraday screens, which host an excessive regular magnetic field on parsec scales, is not yet clear. Rotation measure (RM) surveys of pulsars and extragalactic sources reveal the large-scale magnetic fields in the Galaxy and their direction. 'Cosmic magnetismn' is one of the key-science projects for the planned Sqare Kilometre Array (SKA), which is based on a sensitive RM sky survey with an unprecedented high source density. The analysis of these data will provide magnetic field information on Galactic structures on all scales, but also on far distant extragalactic magnetic fields.