Original Planck maps of M 99 at 1.38 mm and 2.1 mm (top panels), overlaid with the circles used for computing the growth curve. The modelled sky maps are shown in the central panels. Bottom panels show the growth curves computed on the original Planck maps (red solid lines) and on the sky-subtracted maps (green solid lines). The blue-filled circles indicate the value of the integrated flux, corresponding to the yellow circles in the top panels (r = 300″).