M31 is an exceptional galaxy with respect to magnetic fields and cosmic rays. The field in M31 is very regular and extends far beyond the radio-emitting regions. Surprisingly, the origin of the "ring" is still unexplained.
Surface brightness in M31 is low so that polarization observations with higher resolution will be possible only with next-generation radio telescopes like the Square Kilometer Array. This will also allow to observe more RMs from background sources and the detection of pulsars in M31.