Zoom of the F_p map in correspondence of some sources analysed in this work with overlaid radio contours (1283 MHz), from 3σ_I and scaling by a factor of 2. The 6σ_QU and 3σ_I detection thresholds were imposed in polarisation and in total intensity and only pixels above them are shown. Values were corrected for the Ricean bias. Panel (a): T1. Panel (b): T2 and W1. Panel (c): W2 and Group G. Panel (d): FRII. Spatial scales and resolution beam are reported on the edges of the images.