3C 236: middle panel: contours show continuum (same contour levels as Fig. 1). Grayscale shows the mean opacity over the rest frame velocity range −192 km s^-1 to  + 167 km s^-1. The beam FWHM is indicated in the lower right corner. The surrounding spectra show the absorption profiles at different locations indicated by the arrows. The dashed lines indicate the location of the two position–velocity slices presented in Fig. 5.