Unified Schemes for Radio-Loud Active Galactic Nuclei
C. Megan Urry,Paolo Padovani +1 more
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TLDR
In this article, the authors describe radio-loud active galactic nuclei (AGN) and summarize the evidence for anisotropic emission, and outline the two most plausible unified schemes.Abstract:
The appearance of active galactic nuclei (AGN) depends so strongly on orientation that our current classification schemes are dominated by random pointing directions instead of more interesting physical properties. Light from the centers of many AGN is obscured by optically thick circumnuclear matter and in radio-loud AGN, bipolar jets emanating from the nucleus emit light that is relativistically beamed along the jet axes. Understanding the origin and magnitude of radiation anisotropies in AGN allows us to unify different classes of AGN; that is, to identify each single, underlying AGN type that gives rise to different classes through different orientations.
This review describes the unification of radio-loud AGN, which include radio galaxies, quasars, and blazars. We describe the classification and properties of AGN and summarize the evidence for anisotropic emission. We outline the two most plausible unified schemes for radio-loud AGN, one linking quasars and luminous radio galaxies and another linking BL~Lac objects and less luminous radio galaxies. Using the formalism appropriate to samples biased by relativistic beaming, we show the population statistics for two schemes are in accordance with available data. We analyze the possible connections between low- and high-luminosity radio-loud AGN. We review potential difficulties with unification and conclude that none currently constitutes a serious problem. We discuss likely complications to unified schemes that are suggested by realistic physical considerations; these will be important to consider when more comprehensive data for larger complete samples become available. We conclude with a list of the ten questions we believe are the most pressing in this field.read more
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Journal ArticleDOI
Spectroscopic Target Selection in the Sloan Digital Sky Survey: The Quasar Sample
Gordon T. Richards,Xiaohui Fan,Heidi Jo Newberg,Michael A. Strauss,Daniel E. Vanden Berk,Donald P. Schneider,Brian Yanny,Adam N. Boucher,Scott Burles,Scott Burles,Joshua A. Frieman,Joshua A. Frieman,James E. Gunn,Patrick B. Hall,Patrick B. Hall,Željko Ivezić,Stephen B. H. Kent,Stephen B. H. Kent,Jon Loveday,Robert H. Lupton,Constance M. Rockosi,David J. Schlegel,Chris Stoughton,Mark SubbaRao,Donald G. York +24 more
TL;DR: In this paper, the authors describe an automated algorithm for selecting quasar candidates for optical spectroscopy in the Sloan Digital Sky Survey, which is sensitive to quasars at all redshifts lower than z ~ 5.8.
Journal ArticleDOI
The second catalog of active galactic nuclei detected by the Fermi Large Area Telescope
Markus Ackermann,Marco Ajello,Alice Allafort,Elisa Antolini,Elisa Antolini,W. B. Atwood,Magnus Axelsson,Magnus Axelsson,Luca Baldini,Jean Ballet,Guido Barbiellini,Guido Barbiellini,Denis Bastieri,Denis Bastieri,Keith Bechtol,Ronaldo Bellazzini,B. Berenji,Roger Blandford,E. D. Bloom,Emanuele Bonamente,Emanuele Bonamente,A. W. Borgland,Eugenio Bottacini,A. Bouvier,Johan Bregeon,M. Brigida,M. Brigida,P. Bruel,R. Buehler,T. H. Burnett,S. Buson,S. Buson,G. A. Caliandro,R. A. Cameron,P. A. Caraveo,J. M. Casandjian,E. Cavazzuti,C. Cecchi,C. Cecchi,Eric Charles,C. C. Cheung,C. C. Cheung,James Chiang,Stefano Ciprini,R. Claus,Johann Cohen-Tanugi,Jan Conrad,Jan Conrad,L. Costamante,S. Cutini,A. De Angelis,F. de Palma,F. de Palma,Charles D. Dermer,Seth Digel,E. Do Couto E Silva,Persis S. Drell,R. Dubois,L. Escande,C. Favuzzi,C. Favuzzi,Stephen Fegan,Elizabeth C. Ferrara,Justin D. Finke,W. B. Focke,P. Fortin,M. Frailis,Yasushi Fukazawa,Stefan Funk,P. Fusco,P. Fusco,F. Gargano,Dario Gasparrini,Neil Gehrels,S. Germani,S. Germani,B. Giebels,Nicola Giglietto,Nicola Giglietto,Paolo Giommi,F. Giordano,F. Giordano,Marcello Giroletti,T. Glanzman,G. Godfrey,I. A. Grenier,J. E. Grove,Sylvain Guiriec,Mats Gustafsson,Daniela Hadasch,M. Hayashida,M. Hayashida,E. Hays,S. E. Healey,D. Horan,Xian Hou,R. E. Hughes,G. Iafrate,Gudlaugur Johannesson,A. S. Johnson,W. N. Johnson,T. Kamae,Hideaki Katagiri,Jun Kataoka,Jürgen Knödlseder,Jürgen Knödlseder,M. Kuss,J. Lande,S. Larsson,Luca Latronico,Francesco Longo,Francesco Longo,F. Loparco,F. Loparco,Benoit Lott,M. N. Lovellette,P. Lubrano,P. Lubrano,G. M. Madejski,M. N. Mazziotta,W. McConville,W. McConville,Julie McEnery,Julie McEnery,Peter F. Michelson,W. Mitthumsiri,Tsunefumi Mizuno,A. A. Moiseev,A. A. Moiseev,C. Monte,C. Monte,M. E. Monzani,E. Moretti,E. Moretti,A. Morselli,Igor V. Moskalenko,S. Murgia,Takeshi Nakamori,M. Naumann-Godo,P. L. Nolan,Jay P. Norris,E. Nuss,M. Ohno,T. Ohsugi,Akira Okumura,Nicola Omodei,M. Orienti,E. Orlando,J. F. Ormes,M. Ozaki,David Paneque,David Paneque,D. Parent,D. Parent,Melissa Pesce-Rollins,M. Pierbattista,Silvia Piranomonte,F. Piron,G. Pivato,T. A. Porter,S. Rainò,S. Rainò,Riccardo Rando,Riccardo Rando,M. Razzano,M. Razzano,Soebur Razzaque,A. Reimer,Olaf Reimer,Steven Ritz,L. S. Rochester,Roger W. Romani,M. Roth,Daniel Sánchez,C. Sbarra,Jeffrey D. Scargle,T. L. Schalk,Carmelo Sgrò,M. S. Shaw,E. J. Siskind,Gloria Spandre,P. Spinelli,P. Spinelli,Andrew W. Strong,D. J. Suson,Hiroyasu Tajima,Hiroyasu Tajima,Hiromitsu Takahashi,Tadayuki Takahashi,Takaaki Tanaka,J. G. Thayer,J. B. Thayer,D. J. Thompson,L. Tibaldo,L. Tibaldo,M. Tinivella,Diego F. Torres,Diego F. Torres,Gino Tosti,Gino Tosti,Eleonora Troja,Yasunobu Uchiyama,Justin Vandenbroucke,V. Vasileiou,Giacomo Vianello,V. Vitale,V. Vitale,A. P. Waite,E. Wallace,P. Wang,Brian L Winer,D. L. Wood,D. L. Wood,K. S. Wood,Stephan Zimmer +214 more
TL;DR: The second catalog of active galactic nuclei (AGNs) detected by the Fermi Large Area Telescope (LAT) in two years of scientific operation is presented in this article, which includes 1017 γ-ray sources located at high Galactic latitudes (|b| > 10°) that are detected with a test statistic (TS) greater than 25 and associated statistically with AGNs.
Journal ArticleDOI
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Timothy M. Heckman,Philip Best +1 more
TL;DR: In this paper, the authors present a picture in which the population of active galactic nuclei (AGNs) can be divided into two distinct populations: radiative-mode AGNs are associated with black holes that produce radiant energy powered by accretion at rates in excess of ∼ 1% of the Eddington limit.
Journal ArticleDOI
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TL;DR: In this article, the authors proposed the "accretion disk plus wind" model for radio-quiet active galactic nuclei (AGN) and blazars, which is the most appropriate model at present.
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Supermassive Black Holes in Galactic Nuclei: Past, Present and Future Research
TL;DR: The current status of supermassive black hole research, as seen from a purely observational standpoint, can be found in this article, where the authors present a review of the state of the art.
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