The large scale structure of the Galactic magnetic field

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 e lectron density distribution (Taylor & Cordes, 1993) that explicitly accoun ts for the electron density variations due to the spiral structure in our g alaxy. We examine various models to assess the possibility that the magneti c field strength and the electron density may have correlated variations. O ur analysis shows that in most of the regions the `net' field is stronger i n the interarm regions rather than in the spiral arms, and the model in whi ch the large-scale magnetic field is positively correlated with the electro n density can be rejected with a high degree of confidence based on the pul sar RM data. (C) 1998 Elsevier Science B. V. All rights reserved.