Active Galactic Nuclei: what's in a name?

Abstract

Active Galactic Nuclei (AGN) are energetic astrophysical sources powered by accretion onto supermassive black holes in galaxies, and present unique observational signatures that cover the full electromagnetic spectrum over more than twenty orders of magnitude in frequency. The rich phenomenology of AGN has resulted in a large number of different "flavours" in the literature that now comprise a complex and confusing AGN "zoo". It is increasingly clear that these classifications are only partially related to intrinsic differences between AGN, and primarily reflect variations in a relatively small number of astrophysical parameters as well the method by which each class of AGN is selected. Taken together, observations in different electromagnetic bands as well as variations over time provide complementary windows on the physics of different sub-structures in the AGN. In this review, we present an overview of AGN multi-wavelength properties with the aim of painting their "big picture" through observations in each electromagnetic band from radio to gamma-rays as well as AGN variability. We address what we can learn from each observational method, the impact of selection effects, the physics behind the emission at each wavelength, and the potential for future studies. To conclude we use these observations to piece together the basic architecture of AGN, discuss our current understanding of unification models, and highlight some open questions that present opportunities for future observational and theoretical progress.

Accepted for publication in Astronomy & Astrophysics Review, 56 pages, 25 figures

References in corpus (118)

• The EAGLE project: Simulating the evolution and assembly of galaxies and their environments
• X-ray Properties of Black-Hole Binaries
• The Host Galaxies and Classification of Active Galactic Nuclei
• The James Webb Space Telescope
• A Cosmological Framework for the Co-Evolution of Quasars, Supermassive Black Holes, and Elliptical Galaxies: I. Galaxy Mergers & Quasar Activity
• A luminous quasar at a redshift of z = 7.085
• Modelling the behaviour of accretion flows in X-ray binaries
• Simulating galaxy formation with black hole driven thermal and kinetic feedback
• The Co-Evolution of Galaxies and Supermassive Black Holes: Insights from Surveys of the Contemporary Universe
• COSMOS Photometric Redshifts with 30-bands for 2-deg2
• An Observational Determination of the Bolometric Quasar Luminosity Function
• The synthesis of the cosmic X-ray background in the Chandra and XMM-Newton era
• The spectrum of isotropic diffuse gamma-ray emission between 100 MeV and 820 GeV
• Modeling the Time Variability of SDSS Stripe 82 Quasars as a Damped Random Walk
• Toward the Standard Population Synthesis Model of the X-Ray Background: Evolution of X-Ray Luminosity and Absorption Functions of Active Galactic Nuclei Including Compton-Thick Populations
• The X-ray-to-Optical Properties of Optically-Selected Active Galaxies Over Wide Luminosity and Redshift Ranges
• The Chandra Deep Field-South Survey: 7 Ms Source Catalogs
• The Sloan Digital Sky Survey Quasar Catalog: twelfth data release
• Hot and cold gas accretion and feedback in radio-loud active galaxies
• Mid-IR Galaxy Classification Based on Silicate Obscuration and PAH Equivalent Width
• The Pan-STARRS1 distant z>5.6 quasar survey: more than 100 quasars within the first Gyr of the universe
• The diversity of quasars unified by accretion and orientation
• Photometric redshift and classification for the XMM-COSMOS sources
• Simultaneous X-ray/optical/UV snapshots of active galactic nuclei from XMM-Newton: spectral energy distributions for the reverberation mapped sample
• Cosmic X-ray Surveys of Distant Active Galaxies: The Demographics, Physics, and Ecology of Growing Supermassive Black Holes
• Space Telescope and Optical Reverberation Mapping Project. II. Swift and HST Reverberation Mapping of the Accretion Disk of NGC 5548
• Obscuration-dependent evolution of Active Galactic Nuclei
• A Significant Population of Very Luminous Dust-Obscured Galaxies at Redshift z ~ 2
• Testing thermal reprocessing in AGN accretion discs
• Resolving the complex structure of the dust torus in the active nucleus of the Circinus galaxy
• The Imprint of The Extragalactic Background Light in the Gamma-Ray Spectra of Blazars
• CIV 1549 as an Eigenvector 1 Parameter for Active Galactic Nuclei
• Think Outside the Color Box: Probabilistic Target Selection and the SDSS-XDQSO Quasar Targeting Catalog
• The Fermi-LAT high-latitude Survey: Source Count Distributions and the Origin of the Extragalactic Diffuse Background
• The Origin of the Extragalactic Gamma-Ray Background and Implications for Dark-Matter Annihilation
• Optical spectroscopy and X-ray detections of a sample of quasars and AGN selected in the mid-infrared from two Spitzer wide-area surveys
• The First Hyper-Luminous Infrared Galaxy Discovered by WISE
• Correcting CIV-Based Virial Black Hole Masses
• The faint radio sky: radio astronomy becomes mainstream
• Half of the Most Luminous Quasars May Be Obscured: Investigating the Nature of WISE-Selected Hot, Dust-Obscured Galaxies
• The Evolution of Galaxy Number Density at z < 8 and its Implications
• The Half Million Quasars (HMQ) Catalogue
• A Unified Catalog of Radio Objects Detected by NVSS, FIRST, WENSS, GB6, and SDSS
• The Most Luminous Galaxies Discovered by WISE
• Swift monitoring of NGC 5548: X-ray reprocessing and short term UV/optical variability
• The ALHAMBRA Project: A large area multi medium-band optical and NIR photometric survey
• Observations of Mkn 421 with the MAGIC Telescope
• Time-correlation between the radio and gamma-ray activity in blazars and the production site of the gamma-ray emission
• Submillimeter Follow-up of WISE-Selected Hyperluminous Galaxies
• Discovery of multiple Lorentzian components in the X-ray timing properties of the Narrow Line Seyfert 1 Ark 564
• A pilot study of the radio-emitting AGN population: the emerging new class of FR0 radio-galaxies
• The X-Ray Luminosity--Mass Relation for Local Clusters of Galaxies
• The FIRST-2MASS Red Quasar Survey
• A new method to separate star forming from AGN galaxies at intermediate redshift: The submillijansky radio population in the VLA-COSMOS survey
• 9.7 um Silicate Features in AGNs: New Insights into Unification Models
• Spitzer IRS spectra of a large sample of Seyfert galaxies: a variety of infrared SEDs in the local AGN population
• The VLA-COSMOS 3~GHz Large Project: Cosmic evolution of radio AGN and implications for radio-mode feedback since z~5
• Reliable Identification of Compton-thick Quasars at z~2: Spitzer Mid-IR spectroscopy of HDF-oMD49
• An optical spectroscopic survey of the 3CR sample of radio galaxies with z<0.3. I. Presentation of the data
• A large population of mid-infrared selected, obscured active galaxies in the Bootes field
• High-Velocity Bipolar Molecular Emission from an AGN Torus
• Correlated X-ray/Optical Variability in the Quasar MR2251-178
• Mass Functions of the Active Black Holes in Distant Quasars from the Sloan Digital Sky Survey Data Release 3
• On the two main classes of Active Galactic Nuclei
• Optical variability of AGN in the PTF/iPTF survey
• Detailed Shape and Evolutionary Behavior of the X-ray Luminosity Function of Active Galactic Nuclei
• Active galactic nuclei at z ~ 1.5: I. Spectral energy distribution and accretion discs
• Dust-free quasars in the early Universe
• The NuSTAR View of Nearby Compton-thick AGN: The Cases of NGC 424, NGC 1320 and IC 2560
• The cosmic growth of the active black hole population at 1<z<2 in zCOSMOS, VVDS and SDSS
• Multi-phase Nature of a Radiation-Driven Fountain with Nuclear Starburst in a Low-mass Active Galactic Nucleus
• Heavily reddened type 1 quasars at z > 2 I: Evidence for significant obscured black-hole growth at the highest quasar luminosities
• The origin of most massive black holes at high-z: BLUETIDES and the next quasar frontier
• The variability plane of accreting compact objects
• The spectral energy distribution of compact jets powered by internal shocks
• Radio galaxies in the 2SLAQ Luminous Red Galaxy Survey: I. The evolution of low-power radio galaxies to z~0.7
• Mid-Infrared Colors of Dwarf Galaxies: Young Starbursts Mimicking Active Galactic Nuclei
• 2WHSP: A catalog of HE and VHE gamma-ray blazars and blazar candidates
• Dust-Deficient Palomar-Green Quasars and the Diversity of AGN Intrinsic IR Emission
• Weak Hard X-ray Emission from Broad Absorption Line Quasars: Evidence for Intrinsic X-ray Weakness
• NuSTAR unveils a Compton-thick Type 2 quasar in Mrk 34
• Discovery of a ~2 hr high frequency X-ray QPO and iron K alpha reverberation in the active galaxy MS 2254.9-3712
• Extended silicate dust emission in PG QSOs
• Properties of dusty tori in AGN: I. The Case of SWIRE/SDSS Quasars
• Long-Term X-ray Variability of Typical Active Galactic Nuclei in the Distant Universe
• Radio-Quiet Quasars in the VIDEO Survey: Evidence for AGN-powered radio emission at S_1.4GHz < 1 mJy
• The Mid-Infrared Emission of M87
• Submillimetre observations of WISE-selected high-redshift, luminous, dusty galaxies
• Tracing the accretion history of supermassive Black Holes through X-ray variability: results from the Chandra Deep Field-South
• Ensemble X-ray variability of Active Galactic Nuclei. II. Excess Variance and updated Structure Function
• High-frequency X-ray variability as a mass estimator of stellar and supermassive black holes
• Spitzer IRAC Infrared Colours of Submillimetre-bright Galaxies
• Galaxy gas as obscurer: I. GRBs x-ray galaxies and find a N_H ~ M* relation
• Measuring Quasar Variability with Pan-STARRS1 and SDSS
• A Connection between Obscuration and Star Formation in Luminous Quasars
• X-ray spectral variability of Seyfert 2 galaxies
• Automated physical classification in the SDSS DR10. A catalogue of candidate Quasars
• A complete census of silicate features in the mid-infrared spectra of active galaxies
• A simplified view of blazars: contribution to the X-ray and gamma-ray cosmic backgrounds
• Compton Thick AGN in the 70 Month Swift-BAT All-Sky Hard X-ray Survey: a Bayesian approach
• INTEGRAL observations of the blazar Mrk 421 in outburst (Results of a multi-wavelength campaign)
• Variability-selected Active Galactic Nuclei in the VST-SUDARE/VOICE Survey of the COSMOS Field
• Consistency of the black hole mass determination in AGN from the reverberation and the X-ray excess variance method
• Deep, wide-field, global VLBI observations of the Hubble Deep Field North and Flanking Fields
• The Mid-Infrared Properties of X-ray Sources
• The evolution of galaxies resolved in space and time: an inside-out growth view from the CALIFA survey
• Spitzer Space Telescope Measurements of Dust Reverberation Lags in the Seyfert 1 Galaxy NGC 6418
• Hard X-ray selected AGNs in low-mass galaxies from the NuSTAR serendipitous survey
• A New Compton-thick AGN in our Cosmic Backyard: Unveiling the Buried Nucleus in NGC 1448 with NuSTAR
• Novel calibrations of virial black hole mass estimators in active galaxies based on X-ray luminosity and optical/NIR emission lines
• Searching for $\gamma$-ray signature in WHSP blazars: Fermi-LAT detection of 150 excess signal in the 0.3-500 GeV band
• Spatially-Resolved Spectra of the "Teacup" AGN: Tracing the History of a Dying Quasar
• A simplified view of blazars: the very high energy gamma-ray vision
• On the fraction of X-ray obscured quasars in the local universe
• Radiative transfer modelling of parsec-scale dusty warped discs
• Validation of a new background discrimination method for the TACTIC TeV $\gamma$-ray telescope with Markarian 421 data
• Testing the Completeness of the SDSS Colour Selection for Ultramassive, Slowly Spinning Black Holes
• The Road to Quasars

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• Observational Constraints on the Feeding of Supermassive Black Holes
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• Active Galactic Nuclei and their Large-scale Structure: an eROSITA mock catalogue
• LLAMA: The $M_{BH}$ - ${\sigma }_{\star }$ Relation of the most luminous local AGNs
• Composite Spectral Energy Distributions and Infrared-Optical Colors of Type 1 and Type 2 Quasars
• Investigation on Young radio AGNs based on SDSS spectroscopy
• CLOUDY view of the warm corona
• F-GAMMA: Multi-frequency radio monitoring of Fermi blazars. The 2.64 to 43 GHz Effelsberg light curves from 2007-2015
• A Uniformly Selected, All-Sky, Optical AGN Catalog
• Optically variable active galactic nuclei in the 3 yr VST survey of the COSMOS field
• Incoherent fast variability of X-ray obscurers. The case of NGC 3783
• Cloud coalescence: a dynamical instability affecting multiphase environments
• Active Galactic Nuclei: Boon or Bane for Biota?
• Exploring the Diversity of Type 1 Active Galactic Nuclei Identified in SDSS-IV/SPIDERS
• Unveiling the origin of the gamma-ray emission in NGC 1068 with the Cherenkov Telescope Array
• Jet Power of Jetted Active Galactic Nuclei: Implication for Evolution and Unification
• Imaging the AGN Torus in Cygnus
• Extreme & High Synchrotron Peak Blazars beyond 4FGL: The 2BIGB $\gamma$-ray catalogue
• Multiband optical flux density and polarization microvariability study of optically bright blazars
• Optical Variability of the TeV Blazar 1ES 0806+524 on Diverse Timescales
• Extremely High energy peaked BL Lac nature of the TeV blazar Mrk 501
• Characterizing the WISE-selected Heavily Obscured Quasar Population with Optical Spectroscopy from the Southern African Large Telescope
• A Near Infrared View of Nearby Galaxies: The Case of NGC 6300
• Alma Reveals A Gas-rich, Maximum-starburst In The Hyperluminous, Dust-obscured Quasar W0533-3401 AT $z\sim 2.9$
• X-ray reverberation lags from the 1.5 Seyfert galaxy NGC 5273
• Unveiling the 100 pc scale nuclear radio structure of NGC 6217 with e-MERLIN and the VLA
• Understanding the giant gamma-ray outburst on June 16, 2015 from the blazar 3C 279
• Observations of X-ray reverberation around black holes
• Cosmological evolution of quasar radio emission in the view of multifractality
• A relativistic orbit model for temporal properties of AGN
• Monitoring the Extragalactic High Energy Sky
• Image Flux Ratios of Gravitationally Lensed HS 0810+2554 with High Resolution Infrared Imaging
• X-ray analysis of the accreting supermassive black hole in the radio galaxy PKS 2251+11
• Do BL Lac Objects and FR I radiogalaxies inhabit the same galaxy environment?