Arm-interarm CO line ratio analysis. Circles indicate the ¹²CO (2–0) line ratio for lines extracted over the apertures shown in Figure A.2. The squares show the CO line ratio from the IRAM 30 m DDT project E02-20. Positions 1–4 are within the interarm of the galaxy, and positions 5 and 6 are in the spiral arm region. We see that both show larger line ratios in the interarm regions, leading us to conclude that the trend we find is not due to issues with the flux calibration uncertainties. The numerical values of the individual points are listed in Table B.1.