¹²CO (2–1)/(1–0) line ratio compared to FUV intensity (left), FUV+22 μm (centre), and infrared colour (right). We only include sight lines with S/N > 5 for the line ratio to minimise scatter from faint ¹²CO lines. We use a working resolution of 27 arcsec. FUV emission follows to some extent young (≤100 Myr) stellar populations. Because FUV can be heavily obscured, we correct using 22 μm data from WISE band-4 observations. To combine FUV and 22 μm, we multiply the 22 μm by a factor 3–24 × 10⁻³. The resulting sum is proportional to the SFR surface density (Leroy et al. 2019). The infrared 70 μm/250 μm colour is a proxy for the dust temperature. We provide the Pearson's linear correlation coefficient, r_p, in each panel. We do not find any evident correlation of the line ratio with either quantity.