Galactic and extragalactic magnetic fields – a concise review R. Beck Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
Received: 26 May 2009 – Revised: 28 Jul 2009 – Accepted: 30 Jul 2009 – Published: 13 Oct 2009
Abstract. The strength of the total magnetic field in our Milky Way from radio
synchrotron measurements is about 6 µG (0.6 nT), averaged over a
radius of about 1 kpc around the Sun. Diffuse polarized radio
emission and Faraday rotation of the polarized emission from pulsars
and background sources show many small-scale magnetic features, but
the overall field structure in our Galaxy is still under debate. –
In nearby galaxies, radio synchrotron observations reveal
dynamically important magnetic fields of 10–30 µG (1–3 nT)
total strength in the spiral arms. Fields with random orientations
are concentrated in spiral arms, while ordered fields (observed in
radio polarization) are strongest in interarm regions and follow the
orientation of the adjacent gas spiral arms. Faraday rotation of the
diffuse polarized radio emission from the disks of spiral galaxies
sometimes reveals large-scale patterns which are signatures of
regular fields generated by dynamos, but in most galaxies the field
structure is more complicated. – Strong magnetic fields are also
observed in radio halos around edge-on galaxies, out to large
distances from the plane. The ordered halo fields usually form an
X-shaped pattern. Diffuse polarized radio emission in the outer
disks and halos is an excellent tracer of galaxy interactions and
ram pressure by the intergalactic medium.
Citation: Beck, R.: Galactic and extragalactic magnetic fields – a concise review, Astrophys. Space Sci. Trans., 5, 43-47, doi:10.5194/astra-5-43-2009, 2009.