Comparing α_{¹²CO(1−0)} trends in M101 and M51. Comparison of radial α_{¹²CO(1−0)} trend in M101(red) and M51(blue). Each panel shows the trend line for both galaxies separately. The trend is determined by binning the α_{¹²CO(1−0)} values of the individual line of sights. The two dashed lines show the 16th and 84th percentile distribution of the combined M51 and M101 α_{¹²CO(1−0)} dataset. The shaded region around the trend line shows the respective 1σ scatter of the respective trend line fit. Left: the trend of α_{¹²CO(1−0)} with galactocentric radius normalized by r₂₅. Center: ¹²CO line ratio R₂₁ correlation. The thick-dashed line shows a linear regression to the stacked data points (combining M51 and M101). The grey-shaded region between the dotted curves indicates the 1σ confidence interval of the fit. Right: trend with the ¹³CO-to-¹²CO line ratio, R_13/12. The linear regression only fits the trend for M51 since no clear trend is seen for M101.