The Zeeman effect in interstellar clouds

Abstract

The interpretation of Zeeman-effect measurements in terms of interstellar magnetic fields is strongly involved with the problems of the nature of interstellar clouds, and of their relationship to the structure of the field. The best measurements furnish, for the mean longitudinal component of the spectrum of Tau A, a value of + 1·1 ± 3·0 μG (micro-gauss), and for that in the Orion-Arm feature in Cas A, - 0·8 ± 3·5 μG. These values are consistent with an upper limit of 7 μG to a uniform magnetic field, pervading the absorbing clouds and directed parallel to the local spiral arm.