The relationship between Mg II broad emission and quasar inclination angle

TL;DR

This study investigates how quasar orientation affects Mg II emission properties in radio-loud quasars, finding no significant correlation with inclination angle and suggesting a non-disk-like Mg II emission region.

Contribution

It provides new evidence that Mg II emission does not depend on quasar inclination, challenging previous assumptions about disk-like emission regions.

Findings

No significant relationship between inclination angle and Mg II FWHM or equivalent width.

Possible negative correlation between inclination angle and Fe II strength.

Some edge-on quasars still show broad emission lines, indicating complex geometry.

Abstract

Several observed spectral properties of quasars are believed to be influenced by quasar orientation. In this investigation we examine the effect of orientation on the Mg II line located at 2798 {\AA} in a sample of 36 radio-loud quasars, with orientation angles having been obtained in a previous study using radio observations. We find no significant relationship between orientation angle and either Mg II line full-width at half-maximum or equivalent width. The lack of correlation with inclination angle contradicts previous studies which also use radio data as a proxy for inclination angle and suggests the Mg II emission region does not occupy a disk-like geometry. The lack of correlation with Mg II equivalent width, however, is reported in at least one previous study. Although the significance is not very strong (86 percent), there is a possible negative relationship between inclination angle and Fe II strength which, if true, could explain the Fe II anti-correlation with [O III ] strength associated with Eigenvector 1. Interestingly, there are objects having almost edge-on inclinations while still exhibiting broad lines. This could be explained by a torus which is either clumpy (allowing sight lines to the central engine) or mis-aligned with the accretion disk.