Nonthermal Emission and Magnetic Fields

  • Yoshiaki Sofue
Part of the Lecture Notes in Physics book series (LNP, volume 935)


Radio observations of the synchrotron radiation from the galactic disk and its polarization give us information about the magnetic field structure of the galaxy. Analyses of polarization vectors and of Faraday rotation measures along the line of sight give us information about the three-dimensional orientation of magnetic fields.Magnetic fields are in pressure equilibrium with the interstellar medium on the order of ∼ 10−12 ergs cm−3. These fields are coupled with interstellar gas, often termed “frozen in” to each other, and influence the hydrodynamic structure of the galactic disk.In the central regions, the magnetic fields accumulate to create strong vertical fields, which are wound by galactic rotation, and produce cosmic jets from the nuclear disks, often exhibiting highlighted cosmic jets from active galactic nuclei nesting supermassive black holes.The strongest, and most compact, magnetic field thus far observed reaches ∼ 1012 G on the surface of neutron stars observed as pulsars. Galactic magnetic fields are on the order of several 10−6 G or ∼ 1 μG. Intergalactic fields are sometimes observed to exhibit about the same order as galactic, ∼ 1 μG.The largest-scale, but weaker, magnetic field may penetrate the universe. Thus far known celestial objects are all magnetized, from the Earth, the Sun, stars, interstellar matter, galaxies, and clusters of galaxies. Only one exception is the universe for which the cosmological isotropy principle is adopted. It might be rather challenging to ask if the universe has the north and south directed by a cosmological magnetic field.


Field Line Radio Source Faraday Rotation Galactic Disk Rotation Measure 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


  1. 1.
    Balbus, S.A., Hawley, J.F.: A powerful local shear instability in weakly magnetized disks. I – linear analysis. II – nonlinear evolution. ApJ 376, 214 (1991) [MRI]Google Scholar
  2. 2.
    Dame, T.M., Hartman, D., Thaddeus, P.: The Milky Way in molecular clouds: a new complete CO survey. ApJ 547, 792 (2001) [CO]Google Scholar
  3. 3.
    Fletcher, A., Beck, R., Shukurov, A., Berkhuijsen, E.M., Horellou, C.: Magnetic fields and spiral arms in the galaxy M51. MNRAS 412, 2396 (2011) [M51 magnetic field]Google Scholar
  4. 4.
    Parker, E.N.: Cosmical Magnetic Fields. Oxford University Press, New York (1979)Google Scholar
  5. 5.
    Planck Collaboration, et al.: Planck intermediate results. XXI. Comparison of polarized thermal emission from Galactic dust at 353 GHz with interstellar polarization in the visible. AA 576, A104 (2015)[Dust polarization]Google Scholar
  6. 6.
    Sofue, Y., Fujimoto, M., Wielebinski, R.: Global structure of magnetic fields in spiral galaxies. ARAA 24, 459 (1986) [Magnetic field in galaxies]Google Scholar
  7. 7.
    Sofue, Y., Machida, M., Kudoh, T.: The primordial origin model of magnetic fields in spiral galaxies. PASJ 62, 1191 (2010) [MHD of BSS field]Google Scholar
  8. 8.
    Taylor A.R., Stil J.M., Sunstrum C.: A rotation measure image of the sky. ApJ 702, 1230 (2009) [RM of radio sources]Google Scholar

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© Springer Nature Singapore Pte Ltd. 2017

Authors and Affiliations

  • Yoshiaki Sofue
    • 1
  1. 1.Institute of AstronomyThe University of TokyoMitakaJapan

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