Small Dense Broad-Line Regions in Active Nuclei

Recent observational studies indicate that the broad-line region (BLR) of AGN may be much smaller than previously thought. One consequence is that the flux of ionizing radiation is considerably larger and the clouds may be denser than assumed in standard photoionization models for these objects. This paper attempts to investigate these questions by exploring realistic cloud distributions over a range of radii and densities. Some simple pressure laws are proposed and integrated over the radial distribution of clouds to obtain the contribution to the line and continuum emission for all parts of the BLR. Photoionization calculations are made at very high densities up to 10 to the 13th/cu cm, and the most important processes that are included are discussed in detail. Hydrogen and helium are approximated at about 100 level systems, three-body recombination contribution to all elements is included, and optical depth effects are fully taken account of. Line profiles are predicted. 87 refs.