THE EVOLUTION OF ACTIVE GALACTIC NUCLEI

This dissertation presents detailed, self-consistent, computer simulations of the evolution of active galactic nuclei. A one-dimensional Fokker-Planck code is used to determine the evolution of the stellar system, and another code which integrates the steady-state, one-dimensional hydrodynamics equations is used to determine the flow profile of the interstellar medium.;The luminosity evolution in these models is characterized by an early phase of Eddington-limited accretion onto the central black hole. During this time the central luminosity increases exponentially on a time scale which is directly proportional to the efficiency of converting mass into energy near the black hole. For an efficiency of 0.1, this time scale is 4 x 10('7) years. The peak luminosity in these models scales with the core mass of the stellar system. In order to attain quasar luminosities (L greater than 10('45) ergs s('-1)), the central stellar density in a galactic nucleus must initially be greater than 10('8)M(,o)pc('-3). The peak luminosity in these models is found to occur at z = 3 if galaxies form at z = 5. This Eddington-limited accretion phase gives a natural explanation for the absence of high z quasars and the duration of peak luminosities in quasars. The luminosity of the central source after peak luminosity depends on the mass injection rate from the stellar system and scales as L (TURN) t('-1.3).;Galactic nuclei exhibit a variety of evolutionary stages characterized by the flow profile of the interstellar medium. The particular stages a given galactic nucleus evolves through depend primarily on its central stellar density. Tightly bound galactic nuclei with central stellar densities greater than 3 x 10('9)M(,o) pc('-3) retain all of the gas liberated by the stellar system, and the interstellar medium remains in a state of pure accretion. Galactic nuclei with central stellar densities less than this value lose some of the gas liberated by the stars in a wind driven by Compton heating. These systems evolve first through a pure accretion phase followed by an interstellar medium flow with an inner accretion region and an outer wind and finally by a second period of pure accretion.