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Table 3 gives a concise description of the general structures of ordered magnetic fields in various galaxy types as observed from radio polarization observations. For most galaxy types only a few cases were observed so far. – “Turbulent” stands for “isotropic turbulent or tangled”, “ordered” for “anisotropic turbulent” or “regular”. “Regular field” refers to additional measurements of Faraday rotation.

For a list of radio polarization observations of galaxies, see Beck & Wielebinski (2013) and updated versions on arXiv. Radio images of total intensity and polarization are compiled on:

Table 3. General field structures in nearby galaxies

Galaxy type Magnetic field structure Regular field

Sc with strong Spiral at inner arm edge and in Strong,
density wave interarm regions, turbulent in arms fluctuating
Sb or Sc with weak Spiral in interarm regions, Moderate,
or moderate density wave turbulent + ordered in arms large-scale
Barred Sc Ordered + turbulent along bar, Moderate
  spiral outside bar
Sa Ordered + turbulent Detected
S0 Not detected Not detected
Interacting spiral Ordered, asymmetric Weak
Spiral with nuclear jets Ordered along jet ?
Flocculent Sc or Sd Spiral + turbulent in disk Weak
Irregular Turbulent in star-forming regions Weak
  + segments of ordered field
Starburst dwarf Turbulent in star-forming regions Not detected
Spheroidal dwarf Not detected Not detected
E without active nucleus Not detected Not detected

The open questions raised in this review may inspire future work:

(1) Morphology:

(2) Origin and amplification:

(3) Dynamical importance:

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