NOEMA maps. (a) Intensity, (b) velocity, and (c) velocity dispersion CO(4→3) maps derived from moments 0, 1, and 2, respectively. Panel (d) shows the continuum map in the LSB, and panel (e) displays the map of the residuals once the central point-like component has been removed. Coordinates are reported as angular separations from the phase center, i.e., the 3C 186 QSO coordinates. The phase center and the CO intensity peak are marked with the symbols + and x, respectively. The northern (N) and southern (S) components are highlighted with arrows (panel a) and ellipses (panel b). In the panels (a-c) the velocity range considered corresponds to the velocity support [-350; 330] km s⁻¹ of the CO(4→3) line, while in panels (d, e) all the 7.7 GHz bandwidth of the LSB is used. Contour levels are superimposed onto both the intensity and continuum maps. They correspond to significance levels of -3, -2, 3, 4, 5, 6, 7, and 9σ (panel a) or -3, -2, 3, 5, 13, and 45σ (panels d, e). Dashed and solid contours refer to negative and positive significance levels, respectively. The dashed ellipses at the bottom right of each panel show the beam size.