Measurements of Magnetic Fields in Interstellar Clouds of Neutral Hydrogen

Abstract

Measurements of the Zeeman effect in 21-cm spectral lines have revealed magnetic fields of 10-20 j.igauss (100 gauss) in the Perseus spiral arm in the direction of Cas A. A field of 3.5 zgauss has been detected in the direction of Tau A, whereas limits of 1, 2.5, and 4.8 g~gauss have been set for other regions in the local spiral arm. Magnetic fields in clouds of neutral hydrogen therefore appear to vary by at least an order of magnitude from one region in the Galaxy to another