Emission-line diagnostics for the existence of thermal accretion disks in active galactic nuclei

The use of the relative strengths of optical and UV emission lines to infer information about the EUV continuum shape is demonstrated. The FeII/H-beta line ratio is strongly dependent on spectral shape, making it a good indicator of the UV spectrum. It is shown how the gravitational influence of a massive black hole may be seen in the nature of gas streaming motions and the orbits of gas clouds in the region where the black hole potential is comparable to the stellar galactic potential.