A Self-Consistent Treatment of the Spectral Line-Driving Radiation Force for Active Galactic Nuclei: Consequences on Ionization and Outflow Strength

It is generally agreed that various outflow components are present in many active galactic nuclei (AGN). These powerful outflows are suspected of producing long-range feedback, likely responsible for producing several known correlations between the supermassive black hole (SMBH) mass and a range of large-scale properties of the host galaxy and intergalactic medium. Thus, quantifying and understanding the associated mass and energy flows is crucial to understanding the observed properties of these AGN, as well as how these objects evolve and interact with their surrounding environments. Multiple explanations for AGN wind acceleration have been proposed. Radiative driving, also known as line-driving, is one such possible mechanism. Line-driven disk winds are a promising hydrodynamical scenario for these outflows, due in part to the high number of resonance lines present in the spectra of many broad absorption line (BAL) quasars. In order for line-driving to launch and maintain an outflow from the accretion disk, there must exist a sufficient number of bound atoms to produce those lines. Thus, the gas must be relatively lowly ionized. This calls the viability of line-driving as a launch mechanism into question, since the outflow material is in close proximity to the central source and can easily become over-ionized. This work seeks to determine if radiative driving can indeed provide a feasible mechanism for accelerating and driving AGN outflows. We do this by modeling ~500 AGN with varying initial SMBH and outflow characteristics, such as accretion rate, black hole mass, and wind velocity. We then implement an explicit calculation of the ionization balance in the outflow material along the radial line of sight (LOS). The strength of the line-driving force at each point along the LOS is found using an updated spectral line list of 5.7 million spectral lines. We also calculate the commonly-used "ionization parameter," which is often taken as a shorthand to describe the overall ionization state of the wind. When treated self-consistently, we find that the explicit calculation of the ionization balance and the line-driving force suggests that this ionization parameter fails to capture a comprehensive view of the outflow's ionization state.