The Redshifted Excess in Quasar C IV Broad Emission Lines

TL;DR

This study investigates the redward asymmetry in CIV broad emission lines of quasars, revealing a significant correlation with radio properties and suggesting different emission mechanisms for radio loud and quiet quasars.

Contribution

It demonstrates a strong correlation between spectral index and CIV redward asymmetry, linking radio core dominance to emission line asymmetries in quasars.

Findings

Radio loud quasars show red or blue excess in CIV lines, with red excess increasing along the jet axis.

Radio quiet quasars tend to have blueshifted CIV emission lines.

Significant correlation between spectral index and CIV redward asymmetry.

Abstract

In this Letter, the Evans and Koratkar Atlas of Hubble Space Telescope Faint Object Spectrograph Spectra of Active Galactic Nuclei and Quasars is used to study the redward asymmetry in CIV broad emission lines (BELs). It is concluded that there is a highly significant correlation between the spectral index from 10 GHz to 1350 $\AA$ and the amount of excess luminosity in the red wing of the CIV BEL ($>99.9999%$ significance level for the full sample and the radio loud subsample independently, but no correlation is found for the radio quiet subsample). This is interpreted as a correlation between radio core dominance and the strength of the CIV redward asymmetry. The data implies that within the quasar environment there is BEL gas with moderately blueshifted emission associated with the purely radio quiet quasar phenomenon (the accretion disk) and the radio jet emission mechanism is associated with a redward BEL component that is most prominent for lines of sight along the jet axis. Thus, radio quiet quasars have CIV BELs that tend to show blueshifted excess and radio loud quasars show either a red or blue excess with the tendency for a dominant red excess increasing as the line of sight approaches the jet axis.