THE NARROW-LINE REGION OF HIGH-LUMINOSITY ACTIVE GALACTIC NUCLEI

We have made high signal-to-noise spectroscopic observations of seven radio-loud quasars with the Faint Object Spectrograph on the Hubble Sp ace Telescope and from the ground at McDonald Observatory and at Kitt Peak National Observatory. The resolution is 300-400 km s-1 over the w avelength range 1000-8500 angstrom, enabling us to separate the broad and narrow components of the emission lines. This is the first study o f the optical and UV narrow lines in such high-luminosity active galac tic nuclei (AGNs). The most important and striking observational resul t is the relative weakness of the narrow ultraviolet lines, assuming t hat they have the same widths as the narrow [O III] lambda5007 emissio n lines. We do not have a single definite detection of a narrow UV lin e in any of the seven quasars. We have measured all the strong optical narrow lines and have derived upper limits to the strengths of narrow lines in the UV. The latter are much weaker than predicted by dust-fr ee photoionization models and also weaker than those typically seen in Seyfert 2 galaxies and narrow-line radio galaxies. There is direct ev idence for the presence of dust with significant reddening, typically E(B-V) approximately 0.5. A comparison of our sample with the previous ly observed Seyfert 2s (Kinney et al.) shows that two explanations for the reddening are needed. One is simple foreground reddening, presuma bly in the host galaxy. However some narrow-line spectra show an unsua lly weak Lyalpha/Hbeta intensity ratio, but apparently case B Halpha/H beta. We interpret this as the result of dust inside the narrow line c louds and show model calculations to support this claim. These and oth er calculations presented in this paper are used to argue that much of the narrow-line region in the high-luminosity objects lies well beyon d the nucleus.