Nearby galaxies

With the angular resolution and sensitivity of LOFAR, it will be possible to obtain low-frequency maps providing completely new information on the relativistic cosmic-ray electrons in nearby galaxies. The cosmic-ray spectrum derived from the radio synchrotron spectrum allows us to study and to understand the origin and propagation of these particles, the energy loss processes and how the propagation is affected by the magnetic fields. Deep LOFAR observations of a sample of spiral and dwarf galaxies are planned to observe diffuse polarised emission and its Faraday rotation from the outer disks and halos. LOFAR’s sensitivity should allow us to detect much fainter emission than with present-day telescopes. An even more sensitive technique to detect regular magnetic fields in galaxies is to observe a grid of Faraday rotation measurements from polarised background sources behind galaxies. This method is independent of the presence of cosmic rays in the galaxy and may allow us to detect regular fields at distances from the disk larger than the detection limit of radio synchrotron emission. The project aims to clarify the origin of galactic magnetic fields. Proposed models are the dynamo which can generate large-scale patterns of regular fields, or the galactic wind where magnetic fields from the disk are blown out and amplified by gas motions. The winds of dwarf galaxies are thought to be especially efficient to enrich the intergalactic space with gas and magnetic fields.