Spectroscopy of bright quasars: emission lines and internal extinction

TL;DR

This study uses optical spectroscopy of bright quasars, many X-ray sources, to analyze emission lines, internal extinction, and host galaxy contributions, improving understanding of quasar engines and their evolution.

Contribution

It provides new measurements of quasar emission lines, redshifts, and classifications, and explores the relationship between internal extinction and absorption locations.

Findings

Host galaxy contribution to optical continuum is significant.

Evidence suggests some absorbing material may lie between the continuum source and broad-line region.

A non-unity slope in extinction relations indicates complex absorption geometry.

Abstract

The main purpose of this work is to improve the existing knowledge about the most powerful engines in the Universe - quasars. Although a lot is already known, we still have only a vague idea how these engines work exactly, why they behave as they do, and what the relation is between their evolution and the evolution of their harboring galaxy. Methods we used are based on optical spectroscopy of visually bright quasars, many of which have recently been discovered as X-ray sources, but eventually missed in color-selected surveys. The spectra typically cover the 4200-7000 AA region, allowing measurements of the characteristics of the hydrogen lines, the FeII contribution, and other lines of interest. We present accurate redshift estimates and Seyfert type classification of the objects. We also show that the contribution of the host galaxy to the optical continuum is non-negligible in many cases, as is the intrinsic AGN absorption. Consequences of not correcting for those factors when estimating different quasar parameters are discussed. We also find some evidence of a non-unity slope in the relation between the internal extinction based on the Balmer decrement and the one on the optical continuum slope, implying, if further confirmed, the intriguing possibility that some absorbing material might actually be located between the continuum source and the broad-line region.