Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Galactic and extragalactic magnetic fields   The current state of research of the Galactic magnetic field is reviewed
critically. The average (equipartition) strength of the total field derived
from radio synchrotron data is 6 +/- 2 muG locally and about 10 +/- 3 muG at 3
kpc Galactic radius. These values agree well with the estimates using the
locally measured cosmic-ray energy spectrum and the radial variation of protons
derived from gamma-rays. Optical and synchrotron polarization data yield a
strength of the local regular field of 4 +/- 1 muG, but this value is an upper
limit if the field strength fluctuates within the beam or if anisotropic fields
are present. Pulsar rotation measures, on the other hand, give only 1.4 +/- 0.2
muG, a lower limit if fluctuations in regular field strength and thermal
electron density are anticorrelated along the pathlength. The local regular
field may be part of a 'magnetic arm' between the optical arms. However, the
global structure of the regular Galactic field is not yet known. Several
large-scale field reversals in the Galaxy were detected from rotation measure
data, but a similar phenomenon was not observed in external galaxies. The
Galactic field may be young in terms of dynamo action so that reversals from
the chaotic seed field are preserved, or a mixture of dynamo modes causes the
reversals, or the reversals are signatures of large-scale anisotropic field
loops. The Galaxy is surrounded by a thick disk of radio continuum emission of
similar extent as in edge-on spiral galaxies. While the local field in the thin
disk is of even symmetry with respect to the plane (quadrupole), the global
thick-disk field may be of dipole type. The Galactic center region hosts highly
regular fields of up to milligauss strength which are oriented perpendicular to
the plane.

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The categories of this paper are: chao-dyn
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The categories of this paper are: funct-an
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The categories of this paper are: solv-int
10
The categories of this paper are: q-bio
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The categories of this paper are: nucl-ex
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The categories of this paper are: stat
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The categories of this paper are: dg-ga
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The categories of this paper are: chem-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: math-ph
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The categories of this paper are: quant-ph
0
The categories of this paper are: hep-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: patt-sol
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The categories of this paper are: comp-gas
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The categories of this paper are: alg-geom