The evolution of active galactic nuclei. III - The effects of relativistic particles on the intercloud medium

Abstract

The papers in this series present numerical simulations of the evolution of active galactic nuclei (AGNs). These calculations self-consistently account for the dynamic evolution of the dense stellar system in a galactic nucleus, the mass-loss rate from the stellar system, the flow profile of the liberated (intercloud) gas, and the fueling and luminosity evolution of the central black hole. In our previous models we only considered the effects of Compton heating on the intercloud medium with a Compton equilibrium temperature of 10^8^ K. More extensive analysis of AGN continuum emission has recently shown that a Compton equilibrium temperature of 10^7^ K is more accurate. If Compton heating is the dominant heating mechanism in active galactic nuclei with this low a Compton equilibrium temperature, then many problems arise concerning the dynamic and ionization state of the intercloud gas. In this paper we investigate the effect of relativistic particle heating on the structure and evolution of the intercloud medium. This is accomplished by associating both a photon and a relativistic particle efficiency with the central black hole. We find that if only 12% of the total energy produced by the central engine in an active nucleus emerges as relativistic particles, the intercloud medium can be heated to a temperature an order of magnitude greater than the Compton equilibrium temperature of the central continuum. This increase in temperature significantly reduces the opacity of the intercloud medium, increases the range in the ionization parameter over which a stable two-phase medium can exist, and reduces the drag imposed on optically thin cloud undergoing radiative acceleration. The models presented in this paper evolve through the same evolutionary stages as our previous models. All models develop a partial wind phase near peak luminosity and have pure accretion flows at early and late times when the central luminosity is small. In this paper we concentrate on the structure and evolution of the intercloud medium during the partial wind phase. Models with different ratios of black hole photon to relativistic particle efficiency are presented to simulate the differences between radio-loud and radio-quiet active galactic nuclei. The addition of relativistic particle heating increases the duration and terminal wind velocity of the wind. The mechanical power in the wind at peak luminosity is increased from 2 x 10^39^ ergs s^-1^ in models without relativistic particle heating to 10^42^ ergs s^-1^ in models with equal relativistic particle and photon luminosities. If the irradiated face of the narrow-line clouds is compressed by the ram pressure of the nuclear wind, it is possible to explain the constancy of the ionization parameter among the line-emitting clouds. Pressures necessary to confine both the broad and the narrow-line clouds are readily obtained. The early luminosity evolution of our models is characterized by an Eddington-limited accretion phase as the mass of the central seed black hole increases. In order for peak luminosities to occur by redshifts of approximately 4.5, galactic nuclei must form by redshifts of approximately 7.