Reference : Fifty Years of Quasars. Quasars Classes and Their Relationships
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Fifty Years of Quasars. Quasars Classes and Their Relationships
D'Onofrio, Mauro [Dipartimento di Astronomia, Università degli Studi di Padova]
Marziani, Paola [INAF, Osservatorio Astronomico di Padova]
Sulentic, Jack W. [Instituto de Astrofísica de Andalucía (CSIC)]
Dultzin, Deborah [Instituto de Astronomia, Universidad Nacional Autonoma de Mexico (UNAM)]
Efimov, Yuri [Crimean Astrophysical Observatory]
Gaskell, Martin [Departamento de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso]
Vestergaard, Marianne [The Dark Cosmology Centre, The Niels Bohr Institute, University of Copenhagen; Steward Observatory and Department of Astronomy, University of Arizona]
Hutsemekers, Damien mailto [Université de Liège - ULg > Département d'astrophys., géophysique et océanographie (AGO) > Astroph. extragalactique et observations spatiales (AEOS) >]
Franceschini, Alberto [Dipartimento di Astronomia, Università degli Studi di Padova]
Laor, Ari [Physics Department, Technion - Israel Institute of Technology]
Grupe, Dirk [The Pennsylvania State University]
Lipari, Sebastian [Observatorio Astronómico de la Univ. Nac. de Córdoba]
Lorenzo, Begoña Garcıa [Instituto de Astrofísica de Canarias]
Mediavilla, Evencio [Instituto de Astrofísica de Canarias]
Boroson, Todd [National Optical Astronomy Observatory]
Eracleous, Mike [Department of Astronomy and Astrophysics and Center for Gravitational Wave Physics, The Pennsylvania State University]
Marquez-Perez, Isabel [Instituto de Astrofísica de Andalucía (CSIC)]
Körding, Elmar [Deparment of Astronomy, Radbound Universiteit Nijmegen]
Falcke, Heino [Deparment of Astronomy, Radbound Universiteit Nijmegen; , ASTRON)]
Fifty Years of Quasars: From Early Observations and Ideas to Future Research
D'Onofrio, M.
Astrophysics and Space Science Library, Volume 386
[en] Physics
[en] 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.
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