Examples of radio images to demonstrate our classification into compact and extended radio sources (Sect. 3.2). Grey-scale images show 1.4 GHz FIRST data (≈5 arcsec resolution). Where available, green contours are from our ∼1 arcsec resolution 1.4 GHz images, and the insets are from our ∼0.3 arcsec resolution 6 GHz images (blue contours; Sect. 2.2). Synthesised beam(s) are represented by appropriately coloured ellipses. Labels provide the galaxy name (Jarvis et al. 2019; Jarvis et al., in prep.), minimum and maximum contour levels, radio sizes from FIRST (R_Maj), and radio luminosities (in log[W Hz⁻¹]). Magenta circles represent the SDSS fibre size. Compact radio sources (top row) are defined as those whose radio emission is dominated within the SDSS fibre, whilst extended sources (bottom four rows) show significant emission outside of the fibre extent.