Observational constraints on models for the interstellar magnetic field in the Galactic disk
National Astronomical Observatories, Chinese Academy of Sciences, Jia 20 DaTun Road, Chaoyang District, Beijing 100012, PR China e-mail: firstname.lastname@example.org; email@example.com
2 Observatoire Midi-Pyrénées, Université Paul Sabatier Toulouse 3, CNRS, 14 Av. Ed. Belin, 31400 Toulouse, France
Accepted: 8 May 2008
Aims. Our purpose is to place firm observational constraints on the three most widely used theoretical models for the spatial configuration of the large-scale interstellar magnetic field in the Galactic disk, namely, the ring, the axisymmetric, and the bisymmetric field models.
Methods. We used the rotation measures (RMs) of low-latitude Galactic pulsars and combined them with their dispersion measures and estimated distances to map out the line-of-sight component of the interstellar magnetic field in the near half of the Galactic disk. We then fit our map of the line-of-sight field to the three aforementioned theoretical field models and discuss the acceptability of each fit, in order to determine whether the considered field model is allowed by the pulsar data or not.
Results. Strictly speaking, we find that all three field models are ruled out by the pulsar data. Furthermore, none of them appears to perform significantly better than the others. From this we conclude that the large-scale interstellar magnetic field in the Galactic disk has a more complex pattern than just circular, axisymmetric, or bisymmetric.
Key words: ISM: magnetic fields / Galaxy: disk / galaxies: magnetic fields
© ESO, 2008