6.5 Opt-IR Diameters
The isophotal and total diameters are compared in Figure 24. The lower panel shows that the NIR isophotal diameter is typically 60-70% that of the blue isophotal diameter for early types, and can be as small as 20-30% for late-types, dwarfs and irregular galaxies. The NIR "total" diameter (upper panel) evidently captures most of the blue light for early-types, but is only 50% that of the blue light for extreme late-types. This stands as a cautionary note to users of the 2MASS extended source catalogùgalaxies appear much smaller in the NIR bands, but their total flux is still, for the most part, recovered using the radial surface brightness profile.