Optical Spectrophotometry of a Complete Sample of 3CR Lobe-dominated Quasars

Abstract

We present results from optical spectrophotometry of 19 of the 25 lobe-dominated quasars in the 3CR complete sample. The optical spectra were obtained with the Hale 5 m telescope at Palomar Observatory, using the blue and red CCDs of the Double Spectrograph, between 1984 and 1992. Additional data from the literature allow us to analyze broad UV/optical emission lines in all 25 objects (100% completeness), with a total of 191 broad-line measurements (far more than the 68 points in the preliminary results presented in the 2002 work of Hough et al.). We examine correlations between the widths of the broad emission lines and several radio-based orientation indicators. These include three measures involving the beamed radio emission on the parsec scale: (1) the prominence of the radio nucleus R, defined as the rest-frame ratio of the nuclear to extended flux density at 5 GHz; (2) an alternate measure of relative strength of the radio nucleus R V , defined as the rest-frame ratio of the 5 GHz radio core luminosity to the optical V-band luminosity; and (3) a pseudoangle pseudo , derived from a rank ordering of sources based on both R and projected linear size L. An additional orientation indicator based on kiloparsec-scale radio emission was also used: the prominence of the straight, inner Very Large Array jets (F j), defined as the rest-frame ratio of the jet to jet-lobe flux density at 5 GHz. We confirm earlier studies demonstrating a strong anticorrelation between R and the FWHM of the Mg ii k2798 line; the FWHM also anticorrelates with R V and pseudo. However, the anticorrelation between R and the FWHM of the C iii] k1909 line originally reported for only 12 objects in the 2002 work of Hough et al. is not seen in the complete sample. To make separate investigations of lines that may originate in two physically distinct regions-the intermediate-line region (ILR) and the very broad line region (VBLR)-we scaled the FWHM measurements to a common mean and standard deviation for each region. The scaled FWHM of ILR lines (C iii] k1909, Mg ii k2798, and H k4861) anticorrelates with R, R V , and pseudo , but the FWHM of the VBLR lines (Ly k1216, N v k1240, C iv k1549, and He ii k1640) shows no evidence of any correlations with these three orientation indicators. These results are consistent with models that divide the broad-line region surrounding the central supermassive black hole into an inner, spherical, high-ionization VBLR and an outer, disklike, low-ionization ILR. These results are also consistent with the unification of core-and lobe-dominated quasars. Simple models fit the log R versus Mg ii k2798 FWHM relationship without unbeamed radio emission or turbulent broad-line cloud velocities; small unbeamed and turbulent components offer slight improvements to the fits, but large contributions are ruled out and the best-fitting range of orientation angles is only mildly restricted ($10-80). Some surprising results are anticorrelations between the C iv k1549 and scaled VBLR line widths and log F j. The explanation for these anticorrelations-and the lack thereof for the main ILR lines-is not obvious but may be related to weaker beaming in the kiloparsec-scale jets.