3.4. Fine structure of the field
M31 was also observed at 20 cm with the VLA with 45" (150 pc) resolution (Beck et al., 1998). The total continuum emission shows remarkable asymmetries: The ring is thin (full half-power width of 300-400 pc) in the northeastern (Fig. 4a) and southwestern quadrants, but thick (width of 700-1000 pc) in the northwestern and southeastern (Fig. 4b) quadrants. The latter quadrant shows several filaments perpendicular to the ring.
The highest resolution (15" or 50 pc) so far was obtained with the VLA at 6 cm in a portion of the southwestern ring (Hoernes, 1997). The polarization vectors show systematic fluctuations around the mean orientation, according to Beck et al. (1989) possibly signatures of Parker instabilities. The fine structure of the irregular field is partly resolved. The largest scale of the turbulent field is about 50 pc, in agreement with results from the Galaxy (e.g. Rand & Kulkarni, 1989).