6. THE MAGNETIC FIELD IN M33

The total emission of M33 at 6 cm (Fig. 6) is diffuse. The spiral arms are hardly visible. Polarized emission is also diffuse, but has a bright maximum between the two northern spiral arms, with a maximum fractional polarization of 30%. M33 differs from M31 in this respect, but is in line with the regular fields observed in the interarm regions of many other spiral galaxies (Beck et al., 1996).

Figure 6. Total intensity of M33 at 6.2 cm, observed with the Effelsberg telescope, smoothed to 3' beamsize. The lengths of the vectors are proportional to the polarized intensities, their orientations have not been corrected for Faraday rotation (Niklas & Beck, unpubl.)

In spite of the diffuse polarized emission, the vectors in Fig. 6 form a regular spiral pattern. The average pitch angle is about 60°, much larger than in M31 and the largest pitch angle observed in any spiral galaxy so far. Faraday rotation in M33 is much smaller than in M31 and does not reveal an obvious systematic pattern. Detailed analysis shows that the field can be described by a mixture of dynamo modes (Fletcher et al., this volume). The claim of a possibly dominating biymmetric field by Buczilowski & Beck (1991) cannot be confirmed with the new data.