Civλ1549 as an Eigenvector 1 Parameter for Active Galactic Nuclei

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Abstract

We have been exploring a spectroscopic unification for all known types of broad line emitting AGN. The 4D Eigenvector 1 (4DE1) parameter space shows promise as a unification capable of organizing quasar diversity on a sequence primarily governed by Eddington ratio. This paper considers the role of Civλ1549 measures with special emphasis on the Civλ1549 line shift as a principal 4DE1 diagnostic. We use HST archival spectra for 130 sources with S/N high enough to permit reliable Civλ1549 broad component measures. We find a Civλ1549BC profile blueshift that is strongly concentrated among (largely radio-quiet: RQ) sources with FWHM(HβBC) � 4000 km s −1 (which we call Population A). Narrow line Seyfert 1 (NLSy1, with FWHM Hβ ≤ 2000 km s −1) sources belong to this population but do not emerge as a distinct class. The systematic blueshift, widely interpreted as arising in a disk wind/outflow, is not observed in broader line AGN (including most radio-loud (RL) sources but also ∼ 25 % of RQ) which we call Population B. We find new correlations between FWHM(Civλ1549BC) and Civλ1549 line shift as well as the equivalent width of Civλ1549. They are seen only in Pop. A sources. Broader-lined sources show random scatter. Civλ1549 measures enhance the apparent dichotomy between sources with FWHM(HβBC) less and greater than 4000 km s −1 (Sulentic et al. 2000a) suggesting that it has more significance in the context of Broad Line Region structure than the more commonly discussed RL vs. RQ dichotomy. Black hole masses computed from

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