The Profiles of H beta and [O iii] lambda 5007 in Radio-loud Quasars

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Abstract

Moderate-resolution (150-300 km s^-1^) spectra of the Hβ-[O III] λ5007 region have been obtained for 41 radio-loud quasars in order to investigate relationships among their broad- and narrow-line profiles, radio structures, and X-ray properties. Comparable spectra from the literature have been included to form a data set of 60 radio-loud quasars with similar numbers of core- and lobe- dominated quasars. A variety of statistical analyses have been performed, including rank correlation tests and principle component analysis, which identify several strong, related trends. The dominant source of variation in the Hβ line profile parameters is related to radio core dominance, which measures the orientation of the central engine in the relativistic- beaming model (both the traditional R and a new core-dominance parameter R_V_ are used). As core dominance increases, the equivalent widths EW_Hβ_ and EW_5007_ decrease, Hβ wings (the red in particular) weaken and Hβ becomes more symmetric, and Fe II/[O III] λ5007 increases. The above changes in Hβ are interpreted as the spectrum- to-spectrum variation of a redshifted, very broad component (FWHM ~ 8000- 9000 km s^-1^). Secondary variations in Hβ appear to involve a narrower component (FWHM ~2000 km s^-1^), with a strength unrelated to the core dominance or luminosity but strongly correlated with the strength off [O III] λ5007. Another set of significantly correlated parameters involves the [O III] λ5007 profile, continuum luminosity, and spectral shape: [O III] λ5007 is broader when the optical-to-X-ray spectral index α_ox_ (F_nu_ α ν^-{alpha_ox_^) and the optical luminosity are larger; the narrow-line (NLR) component of Hβ also gets stronger relative to [O III] λ5007, and there is a component of variation in EW_Hβ_ and EW_5007_ in the sense of a Baldwin effect. These results, as well as some noteworthy non-correlations, are briefly discussed in terms of underlying physical causes and other results from the literature. A quantitative comparison with other classes of active galactic nuclei is deferred to a forthcoming paper.

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