Integrated intensity images of the J = 1−0 transitions of all the CO isotopologues targeted in this work. Line emission is integrated in the velocity range 50−450 km s⁻¹. The common beam size of 3″ (∼50 pc) is shown as a white circle in the bottom left corner of the ¹³C¹⁸O map. The emission of ¹³C¹⁸O is contaminated at the higher velocities in some positions as discussed in Sect. 3.2.1 and shown in Fig. 4. This contamination results in the brighter ¹³C¹⁸O region at position 7 differing from the brightest spot from the other isotopologues approximately at position 9. Marked positions numbered 1 to 14 indicate those selected for spectra extraction and analysis (Sect. 3.2). Nominal positions of the single dish spectra from the literature used for comparison are labelled SD A and B (Sect. 3.1.1).