Distribution of the total emission and apparent B-vectors (E+90°, not corrected for Faraday rotation) of polarized emission from M 101 observed at λ 11.1 cm, overlaid on a greyscale image of the polarized intensity. Contour levels are 3, 6, 12, 24, 36, 48, and 72  mJy/beam area , a vector of 1′  length corresponds to a polarized intensity of 1.5 mJy/beam area . The noise levels are 1.2 mJy/beam area in I and 0.54 mJy/beam area in PI. The beamwidth of is shown in the lower right corner.