EDP Sciences
Free access
Volume 486, Number 3, August II 2008
Page(s) 819 - 828
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20078683
Published online 22 May 2008

A&A 486, 819-828 (2008)
DOI: 10.1051/0004-6361:20078683

Observational constraints on models for the interstellar magnetic field in the Galactic disk

H. Men1, 2, K. Ferrière2, and J. L. Han1

1  National Astronomical Observatories, Chinese Academy of Sciences, Jia 20 DaTun Road, Chaoyang District, Beijing 100012, PR China
    e-mail: ferriere@ast.obs-mip.fr; mh@bao.ac.cn
2  Observatoire Midi-Pyrénées, Université Paul Sabatier Toulouse 3, CNRS, 14 Av. Ed. Belin, 31400 Toulouse, France

Received 17 September 2007 / 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