Theoretical quasar emission-line profiles. I - Curve-of-growth effects on observed profiles

Radiative transfer effects are examined in an investigation of the kinematics of quasar and Seyfert emission-line regions with pancake cloud geometries. Consideration is given only to the effects of limb brightening with the aspect angle of pancake clouds, assuming that all lines lie on a single portion of the curve of growth. This effect is coupled with several simple but plausible ensemble geometries and dynamics, and a number of theoretical emission-line profiles have been generated. It is shown that these profiles differ substantially depending on both the ensemble geometry and the portion of the curve of growth considered; for a given ensemble geometry, optically thick line profiles are different from optically thick profiles. It is shown that, for radiatively driven clouds, ensembles of clouds which have maximum velocities approaching the terminal velocity of the acceleration mechanism never produce acceptable profiles unless the cloud luminosity is a strongly decreasing function of radius.