Distribution of PNe as a function of distance from the centre of the galaxy. The top panel shows the number of PNe contained in concentric elliptical rings with growing semi-major axis. The bottom panel shows the luminosity-specific PNe number density measured in the same rings and normalised of its average value, since we are interested in the trend and not on its absolute value. We show the full sample in blue and the sample with m_[OIII] < 25.5 mag in black.