Stellar Mass Loss in Elliptical Galaxies and the Fueling of Active Galactic Nuclei

Abstract

The connection between some observational properties of active galactic nuclei and their host galaxies is studied using a self-consistent model of galactic evolution which reproduces the main features of elliptical galaxies. It is shown that stellar mass loss, calculated in detail from a mixture of stellar generations, can explain the bolometric luminosities and active nucleus-to-host galaxy luminosity ratios of local quasars residing in ellipticals (i.e., the radio-loud ones), under the hypothesis that the power supply is primarily gravitational. The time dependence of the mass-loss rate, however, seems to be too weak to explain quasar evolution as inferred from observations. Stronger time dependencies could be obtained, for example, with much flatter initial stellar mass functions, but the resulting ellipticals would be totally unrealistic. Therefore, either quasar evolution is much less than presently estimated or, more likely, the evolution is not only in luminosity (i.e., it is not driven mainly by the stellar mass-loss rate of the host galaxy), but some density evolution, possibly due to galaxy interactions, has to be present as well. This could be consistent with very recent observational results on the shape of the quasar luminosity function.