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.