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M. Vestergaard (SAO)
An ultraviolet (UV) spectroscopic study was undertaken of ~130 high-redshift (z ~1.5\,--\,3.5) radio-loud and radio-quiet quasars (QSOs) of moderate brightness for their class. Radio data at a mininum of two frequencies are also available for the radio-loud QSOs. The goals were to analyze the UV line profiles for clues to the fundamental differences between the two QSO types, and to study the relative source inclination effects in the profile shapes of radio-louds and what can be inferred about their apparent central geometry. The adopted approach includes (a) a comparison of radio-loud and radio-quiet samples matched in luminosity and redshift, (b) use of a robust parameter scheme, including the interpercentile parameters presented by Whittle (1985; MNRAS, 213, 1), and (c) a reliable error estimation. Detailed modeling of the line profiles is performed to reduce errors on the measured parameters due to varying signal-to-noise among the spectra. Here the emphasis is on the detailed analysis of the C\,{\sc iv} line profile.
Contrary to some reports, profile differences are found to exist depending on the radio power. Radio-loud QSOs have relatively peakier C\,{\sc iv} lines, stronger, narrower C\,{\sc iv} line cores, and predominantly red asymmetries, while radio-quiets have blue C\,{\sc iv} asymmetries on average. The C\,{\sc iv} full width at half maximum does not correlate with aspect angle in this radio-loud sample, but strong correlations with the full widths of the line base and the half flux interpercentile velocity width are detected which have not been reported earlier. This aspect dependence is similar to that reported for the broad H\beta line in low-z QSOs (e.g., Wills & Browne 1986, Ap.J. 302, 56). The radio-loud C\,{\sc iv} line core does not correlate with aspect angle indicating it is emitted isotropically, in contrast to the line base. The constraints which these results place on a few current models of the broad emission-line region are presented.
The author(s) of this abstract have provided an email address for comments about the abstract: mvestergaard@cfa.harvard.edu