Published in Astronomy and Astrophysics Review, 10, 81, 2000

THE EMISSION LINE SPECTRUM OF ACTIVE GALACTIC NUCLEI AND THE UNIFYING SCHEME

M.P. Véron-Cetty and P. Véron

Observatoire de Haute Provence, CNRS, F-04870 Saint-Michel l'Observatoire, France

Abstract. Recent papers dealing with the most controversial aspects of AGNs are reviewed. They suggest interesting conclusions: all Seyferts can be described by a single parameter, the X-ray column density; radio loud AGNs may host a rapidly spinning black hole and radio quiet AGNs a slowly spinning black hole; high-ionization AGNs (Seyfert galaxies and QSOs) contain an optically thick, geometrically thin accretion disk, while low-ionization AGNs (Liners) contain an optically thin, geometrically thick accretion disk; a number of blazars have been classified as BLLs on the basis of insufficient data; most objects with weak broad emission lines are in fact HPQs; many objects have been called Liners although they are not AGNs but rather the result of stellar activity; type 2 QSOs exist, but are quite inconspicuous if radio quiet.

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