Spherical models of QSO/AGN emission-line clouds

Theoretical models of QSO and Active Galactic Nuclei (AGN) emission lines are presented, assuming spherical cloud geometry. Chapter I considers the emission of a single spherical cloud in the presence of a distant ionizing nonthermal continuum with an assumed power law index of -1. The clouds are modeled as pure hydrogen with 5 levels plus continuum, isothermal, isobaric, utilizing the escape probability approximation. Levels populations and angular-emission functions for appropriate spectral lines are calculated for a single cloud for varying model parameters: pressure, column density, and nonthermal flux. Certain models match observed line ratios. In addition, in comparing spherical clouds to slabs: (1) spheres are less efficient, producing about 20 times lower emission/unit area, (2) the angular emission functions are different. These results imply that covering factors for spherical clouds are larger, and the dynamics of the clouds must be different. Dynamical requirements are examined in Chapter II. For pure radial flow, Lyα profiles are far more symmetric than for slabs, but this type of dynamics must be ruled out by observed symmetry. Orbital dynamics in a plane, however, yields acceptable profiles. An orbital model is explored in which spherical clouds slowly diffuse in from a virialized cluster under gravity