NDLI: Radio Emission from Galactic Disks

Content Provider	Springer Nature Link
Author	Lesch, H.
Copyright Year	1998
Abstract	This paper gives a short overview of the observational results on galactic magnetic fields. Interstellar magnetic fields, as deduced from multi-frequency polarization observations, show a well-ordered structure largely following the spiral arms. In some galaxies an axisymmetric spiral pattern dominates (the field being directed inwards), while others exhibit a dominant bisymmetric spiral field or “mixed modes”, as predicted from non-linear dynamo theory. As long as star formation activity is low, the magnetic fields are rather regular. Strong star formation leads to turbulent cloud motions and supernova explosions, which tangle the field, so that the radio emission is only weakly polarized. As a consequence the highest fractional polarizations and polarized intensities at centimeter wavelengths are found in interarm regions. At decimeter wavelengths, galactic disks become “optically thick” for polarized emission. In NGC 6946 the regular field is concentrated in narrow “magnetic arms” located in between the optical spiral arms. The field cannot simply be frozen into the gas and oriented by a density-wave flow. A galactic dynamo may provide a stable spiral pattern of the field, but non-axisymmetric models are still being developed.
Starting Page	364
Ending Page	372
Page Count	9
File Format	PDF
ISSN	00393169
Journal	Studia Geophysica et Geodaetica
Volume Number	42
Issue Number	3
e-ISSN	15731626
Language	English
Publisher	Kluwer Academic Publishers-Plenum Publishers
Publisher Date	1998-01-01
Publisher Place	New York
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Structural Geology Geophysics/Geodesy Meteorology/Climatology
Content Type	Text
Resource Type	Article
Subject	Geochemistry and Petrology Geophysics

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