Measurements of the 21 centimeter Zeeman effect in high-latitude directions

Abstract

A new series of measurements of the Zeeman effect at 21 cm has been launched using the 140 foot (43 m) telescope of the NRAO. The observations of high-latitude sources reveal tremendous improvement in sensitivity over measurements done in a previous era. The detection of a field of +5.5 μG in the direction of the North Polar Spur, in the H I equivalent of CO cloud 40 of Magnani, Blitz, and Mundy, is reported. Field limits as low as a few microgauss were set in the direction of two very cold H I clouds after only 4 hr of integration. The detection of a field of the order of 7 μG in one of the expanding H I shells observed by Troland and Heiles is confirmed, and the field varies significantly on a scale of 20' (0.6 pc at the shell). The detection of a field in the direction of the Orion region by Heiles and Troland is confirmed in one direction but not in another.