Bibcode
D'Onofrio, Mauro; Marziani, Paola; Sulentic, Jack W.; Dultzin, Deborah; Efimov, Yuri; Gaskell, Martin; Vestergaard, Marianne; Hutsemékers, Damien; Franceschini, Alberto; Laor, Ari; Grupe, Dirk; Lipari, Sebastian; Lorenzo, Begoña Garcıa; Mediavilla, Evencio; Boroson, Todd; Eracleous, Mike; Marquez-Perez, Isabel; Körding, Elmar; Falcke, Heino
Referencia bibliográfica
Fifty Years of Quasars, Astrophysics and Space Science Library, Volume 386. ISBN 978-3-642-27563-0. Springer-Verlag Berlin Heidelberg, 2012, p. 217
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2012
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Descripción
Most of the questions in this chapter deal with sources that do not show
the "classical" broad emission-line spectrum that characterizes the
majority of known AGNs at high and low redshift. If that majority
represents a "parent population" of AGNs, is the apparent absence of
broad lines a result of obscuration, orientation, or different physical
conditions? Can all of the subclasses be unified under the AGN umbrella?
With the unification scheme set in place and assumed to be fundamentally
correct, there are at least four overarching questions: do all type-2
AGNs possess an obscured broad-line region? Or how can we distinguishing
type-2 AGNs without a broad-line region if they exist? Where is the low
end of quasar activity? The least luminous AGNs are the so-called
low-ionization nuclear emission-line regions (LINERs), but it is
legitimate to ask if they are all true AGNs.