your ID: 0203 First Name: Casebeer Last Name: Darrin Affiliation: University of Oklahoma Title: A Review of AGN Broad-line Region Photoionization Models Authors: Darrin A. Casebeer, Karen M. Leighly Topic: 5 Session: oral Abstract: Photoionization codes such as CLOUDY are invaluable for understanding the physical conditions of the gas emitting AGN broad lines. However,the zeroth-order "one zone" model, in which the lines are assumed to be emitted by gas with a single density and ionization parameter illuminated by an average AGN continuum, cannot qualitatively explain or predict the observed line emission. We review observational and theoretical evidence that the following effects are important: 1.) the BLR emission region is comprised of gas with a range of densities and ionization parameters; 2.) the spectral energy distribution of an individual AGN influences the line ratios and kinematics in an observable way; 3.) the column density, in particular the presence of gas optically thin to the hydrogen continuum, influences the line emission. Other effects including the gas metallicity and radiative transfer will be discussed as time permits.