An Experiment to Measure the Magnetic Field of the Galaxy: II. Results and Derivation of Magnetic Field Intensities

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Abstract
The difference in intensity between right- and left-hand circular polarization has been derived as a function of frequency from observations of a number of spectral features. These results were then interpreted in terms of the line-of-sight component of the magnetic field in each feature on the basis of a uniform magnetic field passing through all the clouds which comprise each feature. This latter assumption is justified on the basis of published measurements of the polarization of starlight. Six absorption features in the strong radio sources Cassiopeia A, Cygnus A, Taurus A and Sagittarius A and one emission feature at Dec. = + 10° and R.A. = 4 h 20 m were studied. The four deepest features showed no best-fitting line-of-sight component greater than 7 × 10 −6 gauss. These four results can be combined to provide a best fit to a circular magnetic field parallel to the spiral arms with a magnitude of 6.8 ± 3.2 × 10 −6 gauss directed anticlockwise around the Galaxy. Alternatively, a rather better fit can be obtained to a magnetic field inclined at ∼ 20° to the neutral hydrogen spiral arms with a magnitude of 10 × 10 −6 gauss in the same direction. It is concluded that the average magnetic field in the disk of the Galaxy is ≼ 10 × 10 −6 gauss.

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