Revisiting the Unified Model of Active Galactic Nuclei

By H. Netzer. 2015

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This review describes recent developments related to the unified model of active galactic nuclei (AGNs). It focuses on new ideas about the origin and properties of the central obscurer (torus) and the connection to its surroundings. The review does not address radio unification. AGN tori must be clumpy but uncertainties about their properties persist. Today's most promising models involve disk winds of various types and hydrodynamic simulations that link the large-scale galactic disk to the inner accretion flow. Infrared (IR) studies greatly improved our understanding of the spectral energy distribution of AGNs, but they are hindered by various selection effects. X-ray samples are more complete. The dependence of the covering factor of the torus on luminosity is a basic relationship that remains unexplained. There is also much confusion regarding real type-II AGNs, which do not fit into a simple unification scheme. The most impressive recent results are due to IR interferometry, which is not in accord wit...

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/6eabaaf6c9213266434c70a496f7f23418854dc5

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Citations in the corpus

Active galactic nuclei: what’s in a name? (2017, background): “…indicators for a small subset of the AGN population (e.g. X-ray unabsorbed type 2 AGN and X-ray absorbed type 1 AGN; e.g. Panessa and Bassani 2002; Bianchi et al. 2012) also provide interesting insight into the overall universality of the basic unified model (see Netzer 2015 for a review).”
New Spectral Model for Constraining Torus Covering Factors from Broadband X-Ray Spectra of Active Galactic Nuclei (2018, background): “Reprocessed thermal emission from dust in the torus is observed primarily in the infrared part of the spectrum (see, e.g., Hönig 2012, Netzer 2015 for recent reviews).”
Discovery of 21 New Changing-look AGNs in the Northern Sky (2017, background): “Type 1 AGNs show broad (1,000-20,000 km s−1) and narrow (300-1,000 km s−1) emission lines, while only narrow emission lines are present in Type 2 AGNs (Netzer 2015, and references therein).”
x-cigale: fitting AGN/galaxy SEDs from X-ray to infrared (2020, background): “The model assumes that the central engine is surrounded by a dusty torus (i.e. the AGN unified model; Antonucci 1993; Urry & Padovani 1995; Netzer 2015; Zou et al. 2019).”
Stellar Dynamics and Stellar Phenomena Near a Massive Black Hole (2017, methodology): “This conclusion follows from the cosmic statistics of active galactic nuclei (AGN), which are powered by a MBH (see review by Netzer 2015), from the analysis of gas and stellar dynamics observed in well-resolved galactic nuclei in the nearby universe (Ferrarese & Merritt 2000; Gebhardt et al. 2000;…”
The faint radio sky: radio astronomy becomes mainstream (2016, background): “Netzer (2015) discusses the latest developments for this unified model, while Antonucci (2012) discusses both RL and RQ unifications, with more emphasis on radio sources.”
Now You See It, Now You Don't: The Disappearing Central Engine of the Quasar J1011+5442 (2015, background): “The dichotomy between Type 1 and Type 2 active galactic nuclei (AGN) is among the most studied in astrophysics (for a review, see Netzer 2015).”
The dust covering factor in active galactic nuclei (2016, background): “Further discussions on this and related issues can be found in Merloni et al. (2014) and Netzer (2015).”
The WISE AGN Catalog (2017, background): “At larger distances from the accretion disk, a dusty medium, usually referred to as the “dust torus” (see, e.g., Antonucci 1993; Urry & Padovani 1995; Netzer 2015), absorbs the light of the accretion disk and reemits it in the infrared, dominating the SED at wavelengths longer than ∼1 µm.”
Raining on black holes and massive galaxies: the top-down multiphase condensation model (2016, methodology): “The anisotropic, clumpy distribution may help to explain the large zoology of AGN classifications which arise primarily because of the line-of-sight inclination angle (Netzer 2015 for a review).”
First light for GRAVITY: Phase referencing optical interferometry for the Very Large Telescope Interferometer (2017, background): “3 mas, comparable to the angular size expected from the relation between dust sublimation radius and AGN luminosity (Netzer 2015).”
BAT AGN Spectroscopic Survey. V. X-Ray Properties of the Swift/BAT 70-month AGN Catalog (2017, background): “…keV have shown that the shape of the CXB is significantly flatter (with a photon index Γ ∼ 1.4, e.g., De Luca & Molendi 2004) than * cricci@astro.puc.cl 24 See Beckmann & Shrader (2012); Netzer (2013, 2015); Brandt & Alexander (2015); Ramos Almeida & Ricci (2017) for recent reviews on the subject.”