Abstract
. The total intensity and the linear polarization in the 5W region of M31 have been observed with the Very Large Array (VLA) at 1420 MHz. The high resolution of the observations (HPBW = 40", equivalent to 133 pc at the distance of M31), allows the study of the small scale structure of the polarized emission of this galaxy, and the comparison of the results with the predictions of a model of a ring structure for the magnetic field. Combining our map with maps at 6-cm and 11-cm made in Effelsberg, we could obtain unambiguous values for the rotation measure along the main arm in that region. The derived directions for the intrinsic polarization vectors indicate that the magnetic field lines are parallel to the arms. The variation of the rotation measure, as well as the direction of the intrinsic polarization vectors, show a small deviation with respect to the predictions of the ring model, in the southern part of the arm. Kaq : GALAXIES-STRUCTURE - POLARIZATION
