The large scale structure of the Galactic magnetic field

Abstract

We explore the possibility of refining the description for the large-scale magnetic field in our galaxy using the rotation measures (RM) of pulsars. A major new input in our analysis is the recent comprehensive model of the electron density distribution (Taylor & Cordes, 1993) that explicitly accounts for the electron density variations due to the spiral structure in our galaxy. We examine various models to assess the possibility that the magnetic field strength and the electron density may have correlated variations. Our analysis shows that in most of the regions the ‘net' field is stronger in the interarm regions rather than in the spiral arms, and the model in which the large-scale magnetic field is positively correlated with the electron density can be rejected with a high degree of confidence based on the pulsar RM data.