The activity of an AGN is centered in a small nuclear region. The central engine (possibly a black hole with an accretion disk) illuminates and photoionizes gas lying further out in the broad line region (BLR) and the narrow line region (NLR), so the emission lines and continuum should be strongly related. We study the relations between optical/UV emission lines and the IR to X-ray continua of a low redshift sample of quasars. We show that our data favor a model in which the Baldwin effect can be explained by an accretion disk (AD) model in which limb darkening and the projected surface area of an optically thick, geometrically thin disk combine to cause a viewing-angle dependent apparent UV luminosity and a more isotropic X-ray luminosity. The narrow-line Seyfert 1 (NLS1) UV spectra stood out from the general sample so we initiated a detailed study of sources of this type. We show that the spectra of NLS1s imply a smaller ionization parameter and slightly higher densities of the BLR clouds than found in normal AGN, and suggest that high L/LEdd ratios are responsible for these properties. We also suggest that the L/LEdd ratio is one of the parameters driving the correlations found between optical (known as the Boroson & Green eigenvector 1) and UV emission lines. We carried out a test using the [OII] and [OIII] narrow emission lines to check whether another parameter, such as orientation suggested to drive eigenvector 1, is responsible for the observed emission line correlations. We conclude that neither orientation nor orientation dependent dust obscuration drive eigenvector 1.
American Astronomical Society Meeting Abstracts
- Pub Date:
- December 1999