Colour representation of the molecular ambient gas towards SNR G46.8–0.3 traced by the ¹²CO J = 1–0 (in red) and the ¹³CO J = 1–0 (in green) rotational line emissions. Yellow regions are areas where both CO isotope emissions overlap. The SNR radio continuum radiation at 1.4 GHz from THOR+VGPS surveys is represented in blue. The velocity range used to integrate the CO intensity is shown in the bottom left corner of each panel. The name of the discovered molecular features and their kinematic distances are also labelled. White continuous polygons enclose structures associated with G46.8–0.3. Non-associated clouds localised at the far distance of their central velocity are encircled by green continuous polygons, whereas foreground molecular gas along the line of sight is inside orange dashed polygons. Numbers from 1 to 9 spread out in panels a–c indicate the test regions used to construct the spectra presented in Fig. 8.