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Title:
An 84-μG magnetic field in a galaxy at redshift z = 0.692
Authors:
Wolfe, Arthur M.; Jorgenson, Regina A.; Robishaw, Timothy; Heiles, Carl; Prochaska, Jason X.
Affiliation:
AA(Department of Physics and Center for Astrophysics and Space Sciences, University of California, San Diego, La Jolla, California 92093-0424, USA), AB(Department of Physics and Center for Astrophysics and Space Sciences, University of California, San Diego, La Jolla, California 92093-0424, USA), AC(Astronomy Department, University of California, Berkeley, California 94720-3411, USA), AD(Astronomy Department, University of California, Berkeley, California 94720-3411, USA), AE(UCO-Lick Observatory; University of California, Santa Cruz, Santa Cruz, California 95464, USA)
Publication:
Nature, Volume 455, Issue 7213, pp. 638-640 (2008). (Nature Homepage)
Publication Date:
10/2008
Origin:
NATURE
DOI:
10.1038/nature07264
Bibliographic Code:
2008Natur.455..638W

Abstract

The magnetic field pervading our Galaxy is a crucial constituent of the interstellar medium: it mediates the dynamics of interstellar clouds, the energy density of cosmic rays, and the formation of stars. The field associated with ionized interstellar gas has been determined through observations of pulsars in our Galaxy. Radio-frequency measurements of pulse dispersion and the rotation of the plane of linear polarization, that is, Faraday rotation, yield an average value for the magnetic field of B~3μG (ref. 2). The possible detection of Faraday rotation of linearly polarized photons emitted by high-redshift quasars suggests similar magnetic fields are present in foreground galaxies with redshifts z>1. As Faraday rotation alone, however, determines neither the magnitude nor the redshift of the magnetic field, the strength of galactic magnetic fields at redshifts z>0 remains uncertain. Here we report a measurement of a magnetic field of B~84μG in a galaxy at z = 0.692, using the same Zeeman-splitting technique that revealed an average value of B = 6μG in the neutral interstellar gas of our Galaxy. This is unexpected, as the leading theory of magnetic field generation, the mean-field dynamo model, predicts large-scale magnetic fields to be weaker in the past rather than stronger.
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