Spectroscopy of bright quasars: emission lines and internal extinction^*

¹ Institute of Astronomy, Bulgarian Academy of Sciences, 72 Tsarigradsko Chausse Blvd., 1784 Sofia, Bulgaria e-mail: bachevr@astro.bas.bg
² Royal Observatory of Belgium, Av. Circulaire 3, 1180 Brussels, Belgium e-mail: Anton.Strigachev@oma.be

Received: 23 April 2008
Accepted: 18 June 2008

Abstract

Aims. 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. 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 ÅÅ region, allowing measurements of the characteristics of the hydrogen lines, the FeII contribution, and other lines of interest.

Results. 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.