HST image of 3C 186 (top-left). The host galaxy center is indicated with a blue circle. The orientation of the radio jet is shown as a yellow line. The white arrow indicates the location of the so-called blob of unknown origin, ~ 2 arcsec East-North-East of the quasar point source. Top-right: model of the source, which includes a PSF and a Sérsic model. Bottom-left: residuals after model subtraction. Bottom-right: smoothed (4-pixel kernel) version of the HST image showing the presence of low S/N shells or tidal tails in the host galaxy (indicated by the blue arrow).