Total intensity I (colour) of M 31 at λ3.6 cm smoothed to HPBW, in coordinates along the major and minor axes of M 31. The rms noise is 0.25 mJy beam⁻¹ in the inner part (40′×40′) and 0.3 mJy beam⁻¹ in the outer parts. The lines show the apparent magnetic field orientations (not corrected for Faraday rotation) at the same resolution with lengths proportional to polarized intensity PI, where the length of a beam width corresponds to 0.225 mJy beam⁻¹. No lines are plotted where PI is below 0.15 mJy beam⁻¹ or where I is negative. Background sources have been subtracted. The HPBW is indicated in the bottom left corner.