On the Relation Between Radio and Non-Radio Elliptical Galaxies

Empirical evidence suggests that elliptical galaxies hosting a radio source may not be different from normal non-radio ellipticals. To test this possibility, we use Monte Carlo simulations to reproduce the distribution of radio galaxies in the radio-optical luminosity plane. The input parameters of the simulation are the optical luminosity function (LF) of ellipticals and the radio LF of radio galaxies, linked by a function giving the probability for an elliptical to be a radio galaxy. Simulations reproduce the observations well, supporting unification of radio and non-radio ellipticals, provided that the probability of an elliptical hosting a radio source is proportional to the square of its optical luminosity. The difference of 0.5 magnitudes in average optical luminosity between FRI and FRII radio galaxies is also explained in this framework.