Faraday rotation of the emission from linearly polarized radio sources

Abstract

The variation of Faraday rotation with galactic coordinates is studied for 86 radio sources. It is concluded that most of the rotation takes place in our Galaxy. At low latitudes. |bII| < 20°, the distribution of rotation measure in galactic coordinates is consistent with a magnetic field directed towards lII = 95° ± 10°, which is approximately along the local spiral arm. At intermediate latitudes, 20° < |bII| > 60°, the field is directed towards lII = 95° in southern latitudes but in the opposite direction towards lII = 275° in northern latitudes. At high northern latitudes, bII > 60°, the field appears to be approximately parallel to the plane, but at southern latitudes bII < –60°, it has an inward component towards the plane. An analysis of the scatter of rotation measure observed at high latitudes and in double sources indicates that the mean rotation measure arising in the sources themselves is less than 5 rad/m2.