Luminosity Effects and the Emission-Line Properties of Quasars with 0 < Z < 3.8

Abstract

We present data and a spectral atlas for 76 quasars with 2.97 < z < 3.80 and for 33 quasars with z ~ 2, together with measures of 73 quasars from the IUE archives that mostly have z < 1. The quasars provide a sampling of the luminosity-redshift plane at constant luminosity for 0 < z < 3.8, a range of a factor of 40 in luminosity for 3 < z < 3.8, and a range of 10^3^ in luminosity for z < 1. We investigate the behavior of the principle emission lines from 1200- 2000 A and find: 1. The Baldwin effect at z > 3 is definitely present in the C IV λ1549 line and in the other strong emission lines in varying degrees except for N V λλ1240 and 1400, where the effect is very weak. 2. The component that varies with luminosity has a narrower FWHM than the average line width and appears consistent with the first component of the principal component analysis of the Large Bright Quasar Survey sample by Francis et al. (1992). 3. There is no evidence for redshift-dependent spectral changes, Baldwin or otherwise, in quasars of the same luminosity in the z ~ 2 and z > 3 samples. 4. The Baldwin effect in the IUE, z ~ 2, and z > 3 subsamples joins smoothly, although the slope of the effect steepens with increasing luminosity. 5. The results are consistent with the ionization parameter decreasing with increasing luminosity. 6. The large ratio of N V to Lyα and its small change with luminosity are consistent with the arguments of Hamann & Ferland (1993a, b) that the N/C ratio is enhanced in high-luminosity quasars with z > 3.