Measurements of R_50, gas, R_50, ⋆, and R_50, bar for three example galaxies: a gas-dominated one (UGC 731), a star-dominated one (NGC 2903), and an intermediate case (NGC 5585). The upper panels show the surface density profiles for gas (blue points), stars (red points), and total baryons (black line); the stellar profile was extrapolated at large radii with an exponential function (dashed red line). The lower panel shows the curve of growth of gas (blue line), stars (red line), and total baryons (black line); the dotted lines show the location of the corresponding half-mass radii.