A deep λ20 cm radio continuum survey of M 31

We present a survey of the total and linearly polarized radio continuum emission of the Andromeda galaxy at 20 cm wavelength with the VLA-D array. 7 fields were observed with 45$\prime\prime$angular resolution. The missing large-scale total emission observed with the Effelsberg telescope was inserted. This survey is the most sensitive radio continuum survey of M 31 so far and the first one in linear polarization with the VLA. The total emission of M 31 comes from extended regions and point sources. Both components are concentrated in the bright "ring” of maximum star formation at about 10 kpc radius. Nearly half of the extended emission emerges from numerous filamentary features which are typically a few arcminutes long ($\simeq 600$pc). In the field of M 31, 36 linearly polarized background sources were detected. The smallest degrees of polarization occur on the centre of the "ring” where the total emission is highest, hence on the spiral arms as delineated by Hαemission and OB associations. The distribution of polarization angles reveals coherent features of typically 1 kpc in extent, some of which show a relation to an OB association.