The central engines of radio-loud quasars

Free access article

Issue		A&A Volume 409, Number 3, October III 2003


Page(s)		887 - 898
Section		Galactic structure and dynamics
DOI		http://dx.doi.org/10.1051/0004-6361:20031218

A&A 409, 887-898 (2003)
DOI: 10.1051/0004-6361:20031218

The central engines of radio-loud quasars

J.-M. Wang^{1, 2, 3}, L. C. Ho⁴ and R. Staubert¹

¹ Institut für Astronomie und Astrophysik, Abt. Astronomie, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
² Laboratory for High Energy Astrophysics, Institute of High Energy Physics, CAS, Beijing 100039, PR China
³ Alexander von Humboldt Fellow
⁴ The Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101-1292, USA
e-mail: lho@ociw.edu

(Received 7 October 2002 / Accepted 29 July 2003 )

Abstract
We have assembled a sample of 37 radio-loud quasars that have been imaged with the Hubble Space Telescope in order to investigate their black hole masses, accretion rates, and the structure of their accretion disks. The black hole masses were estimated from the luminosities of the host galaxies, and the accretion powers were extrapolated from the emission-line luminosities. The majority of the quasars have masses in the range $M_{\rm BH} \approx 10^8{-}10^9$ $M_\odot$ . Their accretion rates, $\dot M \approx 0.01{-}1$ times the Eddington rate, suggest that most of the objects possess standard optically thick, geometrically thin accretion disks, in some cases perhaps accompanied by an optically thin advection-dominated component. The coexistence of strong radio emission and a standard disk conflicts with recent models for jet formation. We discuss modifications of the standard model that can resolve this discrepancy. We find there is a strong correlation between the accretion rate and the extended radio luminosity. This lends support to the idea that the extended radio emission is somehow linked to the accretion disk. Lastly, we combine the present sample of radio-loud quasars with the sample of BL Lac objects studied by Wang et al. (2002) to reevaluate the unification picture for radio-loud active galactic nuclei. Consistent with current ideas for the unification of radio-loud sources, we find that flat-spectrum radio quasars and FR II radio galaxies indeed seem to belong to the same population, as do BL Lac objects and FR I radio galaxies on the opposite end of the luminosity spectrum. However, some members of the low frequency-peaked BL Lac objects may be more closely associated with FR II rather than FR I radio galaxies. We describe how the various subclasses of radio-loud sources can be viewed as a continuous sequence of varying accretion rate.

Key words: BL Lacertae objects: general -- galaxies: active -- galaxies: jets -- galaxies: Seyfert -- quasars: general

Offprint request: J.-M. Wang, wang@astro.uni-tuebingen.de

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