Example ¹³CO (6–5) radial profiles for an HII source (G43.17+0.0) (left) and an IRw source (G335.79+0.1) (right). At 5″-wide individual annuli, the median and standard deviation values are presented as filled blue circles and associated ‘error’ bars. Annuli with an insufficient number of detected pixels are indicated as open blue circles and were excluded from the determination of best-fit curves (red).