[O II] Emission, Eigenvector 1, and Orientation in Radio-quiet Quasars

Abstract

We present supportive evidence that the Boroson & Green eigenvector 1 is not driven by source orientation and further that both [O III] λ5007 and [O II] λ3727 are isotropically emitted in the radio-quiet sample of bright quasar survey (BQS) quasars, contrary to results found for radio-loud active galactic nuclei (AGNs). Studies of optical emission lines in quasars have revealed a striking set of correlations between various emission-line properties, known as the Boroson & Green eigenvector 1. Until recently it was generally accepted that eigenvector 1 does not depend on orientation, as it strongly correlates with [O III] λ5007 emission, thought to be an isotropic property. However, recent studies of radio-loud AGNs have questioned the isotropy of [O III] emission and concluded that [O II] λ3727 emission is isotropic. In this paper we investigate the relation between eigenvector 1 and [O II] emission in radio-quiet BQS quasars and readdress the issue of orientation as the driver of eigenvector 1. We account for the small blue bump present at [O II] wavelengths and subtract Fe II emission that contaminates [O III] emission. We find significant correlations between eigenvector 1 and orientation-independent [O II] emission, which implies that orientation does not drive eigenvector 1. The luminosities and equivalent widths of [O III] and [O II] correlate with one another, and the range in luminosities and equivalent widths is similar. This suggests that our radio-quiet BQS quasar sample is largely free of orientation-dependent obscuration and/or ionization effects. We conclude that neither the [O III] emission nor the [O II]/[O III] ratio are dependent on orientation in radio-quiet quasars, contrary to recent results found for radio-loud quasars.