Panel a: 1.4 GHz continuum plotted as contours of (− 2,2,4,8,16,32,64,128) × 0.2 mJy beam^-1 overlaid on a three-colour SDSS image (using the i,r,g bands). NGC 4418 is the white disc in the top-right part of the image, and VV 655 is the blue irregular galaxy near the image centre. In addition to NGC 4418, four other sources are visible above 4σ, as noted in Sect. 3.1. VV 655 is barely detected at 3σ in the radio continuum. Panel b: moment-0 map of the continuum-subtracted HI (in emission and absorption) with contours at (−32,−16,−8,−4,−2,2,4,8,16,32) × 35 mJy beam^-1 km s^-1.