Effective radii derived for the CO(2–1) and Paα tracers using the CoG method. The black dashed line represents the 1:1 relation. The solid green line identifies the derived best fit to the data, which was derived using a linear least squares fit. Two outliers (IC 4687 and ESO 320-G030) are identified for which the R_Paα ≳ R_CO, while NGC 1614 is characterized by R_CO ≳ R_Paα. The most extreme R_Paα is derived for IC 4518 E, and considered as an upper limit (see text for details). IC 5179 is a galaxy that shows similar effective radii for both gas tracers (R_Paα ∼ R_CO).