Fraction of galaxies that host a radio source above a given luminosity limit. The blue curve corresponds to the detected sources, the red curve includes the upper limits and represents the upper envelope of the distribution. The black dot represents the result of the stacking of the 42 undetected galaxies. The black dashed line is a power law with a slope of 0.34. The green dashed line is instead the fit obtained by Best et al. (2005b). The inset shows a zoomed-in look at the lowest luminosities.