Multi-wavelength surface-brightness profiles for the galaxy NGC 5457 (M 101), shown up to r₂₅. The profiles have been shifted for displaying purposes and the corresponding offsets are quoted next to each profile. The profiles are arranged in order of decreasing wavelength, from top to bottom. At the top, the interstellar radiation field intensity U, is shown, in dimensional units. The black dashed lines are exponential fits performed avoiding the central part of galaxies up to the maximum extension of the 70 μm profile (shown in red).