Left panel: ¹³CO J = 1 − 0 and J = 2−1 line profiles (black and red histograms, respectively), averaged over concentric rings of width Δr = 10′′, observed at radii ranging from r = 0′′ to 130′′. The ordinate scale (black numbers) applies to the J = 1 − 0 line profile (black). The number in red in the upper left corner is the factor by which the J = 2−1 profile (red) has been divided to match the intensity scale. For r< 90′′ it also represents the R₂₁ = ¹³CO(2−1)/¹³CO(1−0) velocity-integrated line intensity ratio. Right panel: J = 2−1¹²CO (black) and ¹³CO line profiles averaged over the same 10′′-wide rings. The ordinate scale applies to the ¹³CO(2−1) line profile (red). The number in black in the upper left corner is the factor by which the ¹²CO(2−1) profile (black) has been divided to match the intensity scale. For r ≥ 40′′, it also represents the R_i = ¹²CO(2−1)/¹³CO(2−1) velocity-integrated line intensity ratio.