Top: integrated flux densities of ¹²CO and ¹³CO transitions in the central region (18′′ in diameter) of Circinus. We plot the solution range of ¹²CO (dark gray) and ¹³CO (light gray) derived from single-component LVG modeling of CO and ¹³CO lines with J ≥ 3. The range is selected from all solutions satisfying < 1.5 (or Likelihood L> 0.6). We plot ¹²COJ = 2 → 1, ¹²COJ = 1 → 0, and their ¹³CO isotopic transitions for beam sizes >18′′ as upper limits (black boxes and circles) to our models. Bottom: integrated flux densities of ¹³CO, in a zoomed in view.