Quasars in a merging model: Comparison with the observed luminosity function

The relationship between the luminosity function of quasars and the mass fu nction of galaxies is considered in the framework of a phenomenological mod el in which the birth of active galactic nuclei is associated with galaxy m ergers. Quasars are taken to be short-lived objects whose luminosity is det ermined by the masses and angular momenta of the galaxies whose merger gave rise to the quasar, as well as by their gas content. The masses and angula r momenta of the merging galaxies determine the amount of mass that loses a ngular momentum, and is capable of falling into the center of the system. T he proposed model can explain the shape and evolution of the quasar luminos ity function and is used to estimate the fraction of matter falling into th e center of the merger systems eta (apparently associated with the fraction of gas in the galaxies) and the mean density contrast in the places where quasars form kappa. The resulting values for kappa vary from similar to 4-7 at z = 0.5 to similar to 1-2 at z = 2. The values for eta range from sever al percent at z = 0.5 to tens of percent and even values approaching unity, at z = 2. In contrast to cases considered earlier, an appreciable role is played by the Eddington limit, which can apparently be exceeded in quasars.