CIV Emission and the Ultraviolet through X-ray Spectral Energy Distribution of Radio-Quiet Quasars

TL;DR

This study investigates how CIV emission-line properties in radio-quiet quasars relate to their UV through X-ray spectral energy distribution, revealing correlations between emission features and spectral hardness.

Contribution

It establishes a connection between CIV emission-line characteristics and the UV-X-ray SED in radio-quiet quasars, linking optical/soft X-ray relationships to UV and hard X-ray regimes.

Findings

Strong CIV emission and small blueshifts correlate with hard X-ray spectra.

Weak CIV emission and large blueshifts correlate with soft X-ray spectra.

Results suggest systematic errors in bolometric corrections should be considered.

Abstract

In the restframe UV, two of the parameters that best characterize the range of emission-line properties in quasar broad emission-line regions are the equivalent width and the blueshift of the CIV line relative to the quasar rest frame. We explore the connection between these emission-line properties and the UV through X-ray spectral energy distribution (SED) for radio-quiet (RQ) quasars. Our sample consists of a heterogeneous compilation of 406 quasars from the Sloan Digital Sky Survey and Palomar-Green survey that have well-measured CIV emission-line and X-ray properties (including 164 objects with measured Gamma). We find that RQ quasars with both strong CIV emission and small CIV blueshifts can be classified as "hard-spectrum" sources that are (relatively) strong in the X-ray as compared to the UV. On the other hand, RQ quasars with both weak CIV emission and large CIV blueshifts are instead "soft-spectrum" sources that are (relatively) weak in the X-ray as compared to the UV. This work helps to further bridge optical/soft X-ray "Eigenvector 1" relationships to the UV and hard X-ray. Based on these findings, we argue that future work should consider systematic errors in bolometric corrections (and thus accretion rates) that are derived from a single mean SED. Detailed analysis of the CIV emission line may allow for SED-dependent corrections to these quantities.