Orientation effects on spectral emission features of quasars

TL;DR

This study investigates how the orientation of quasars affects their spectral emission features, confirming EW([OIII]) as a reliable indicator of inclination and explaining related spectral correlations.

Contribution

It demonstrates the impact of quasar orientation on emission line properties and validates EW([OIII]) as an effective inclination indicator using a large SDSS quasar sample.

Findings

Broad line widths increase with EW([OIII])

Blue component diminishes with higher EW([OIII])

Orientation influences the [OIII]-FeII anticorrelation

Abstract

We present an analysis of the orientation effects in SDSS quasar composite spectra. In a previous work we have shown that the equivalent width EW of the [OIII] {\lambda}5008{\AA} line is a reliable indicator of the inclination of the accretion disk. Here, we have selected a sample of ~15,000 quasars from the SDSS 7th Data Release and divided it in sub-samples with different values of EW([OIII]). We find inclination effects both on broad and narrow quasars emission lines, among which an increasing broadening from low to high EW for the broad lines and a decreasing importance of the blue component for the narrow lines. These effects are naturally explained with a variation of source inclination from nearly face-on to edge-on, confirming the goodness of EW([OIII]) as an orientation indicator. Moreover, we suggest that orientation effects could explain, at least partially, the origin of the anticorrelation between [OIII] and FeII intensities, i.e. the well known Eigenvector 1.