Radial surface brightness profile of M 31 (Irwin et al. 2005) (in black) and the PN density using only the PNe within 2.5 mag of the bright cut-off, obtained at different elliptical bins (in blue). The Courteau et al. (2011) decomposition of the M 31 luminosity profile into the bulge, and disc and halo components scaled to the V-band surface brightness profile are also shown. The three-component photometric model for the predicted PN surface density is shown in blue.