Radio polarization and magnetic field structure in M101

We observed total and polarized radio continuum emission from the spiral galaxy M?101 at 6.2 cm and 11.1 cm with the Effelsberg telescope. We use these data to study various emission components in M 101 and properties of the magnetic field. Separation of thermal and non-thermal emission shows that the thermal emission is closely correlated with the spiral arms, while the non-thermal emission is more smoothly distributed indicating diffusion of cosmic ray electrons away from their places of origin. We show that energetic events causing H i?shells of mean diameter < 625 pc could partly be responsible for this. At radii < 24kpc, the random magnetic field depends on the star formation rate/area, SSFR, with a power-law exponent of b = 0.28 [+ or -] 0.02. The ordered magnetic field is generally aligned with the spiral arms with pitch angles that are about 8[degrees] larger than those of H i filaments.