| Abstrakt: |
An overview of line-emitting regions in active galactic nuclei (AGN) is presented. Most existing AGN gas line-intensity measurements are accounted for by detailed photoionization models used in conjunction with spectrophotometric observations. The Seyfert 1 galaxy and quasar picture includes gravity as the primary energy source, and a black hole of 1-10 billion solar masses with a radiating accretion disk. None of the model principal input parameters, which describe physical, chemical, geometric, and energetic details of the picture, is unambiguously understood. Despite refinements in the model calculations from new atomic data, the predicted intensities of most stronger lines have not changed since the 1970's. Knowledge of the broad-line-emitting gas density is crucial for understanding the importance of various physical processes and of complicating effects such as reddening. Other modeling improvements are discussed. |
