Active Galactic Nuclei

Active Galactic Nuclei
Name	Active Galactic Nuclei
Type	Phenomenon

Contents

Active Galactic Nuclei Active Galactic Nuclei are compact regions at the centers of galaxies that emit tremendous amounts of radiation across the electromagnetic spectrum, driven by accretion onto supermassive black holes. They have been studied through coordinated programs and observatories such as Hubble Space Telescope, Chandra X-ray Observatory, Very Large Array, Atacama Large Millimeter/submillimeter Array, and European Southern Observatory. Research initiatives and collaborations including Sloan Digital Sky Survey, Fermi Gamma-ray Space Telescope, Event Horizon Telescope, Gaia (spacecraft), and missions from National Aeronautics and Space Administration, European Space Agency, and Japan Aerospace Exploration Agency have advanced the field.

Introduction

Active galactic nuclei were first implicated by observations of extraordinary emission lines and compact radio sources such as 3C 273, Cygnus A, Messier 87, Centaurus A, and NGC 1068, and interpreted through theoretical work by figures associated with Royal Astronomical Society, Mount Wilson Observatory, Palomar Observatory, Max Planck Institute for Astrophysics, and researchers at California Institute of Technology, Harvard-Smithsonian Center for Astrophysics, Princeton University, University of Cambridge, and University of Chicago. Early debates involved data from instruments like Palomar Hale Telescope and concepts developed in contexts including General Relativity, Quantum Electrodynamics, and models refined by groups at Kavli Institute for Theoretical Physics and Institute for Advanced Study.

Observationally, nuclei show multiwavelength signatures measured by facilities including Keck Observatory, James Webb Space Telescope, Spitzer Space Telescope, Wilkinson Microwave Anisotropy Probe, and Planck (spacecraft), with spectra revealing broad and narrow emission lines first cataloged in surveys such as Two Micron All Sky Survey and ROSAT All-Sky Survey. Variability studies using International Ultraviolet Explorer, RXTE, XMM-Newton, and Swift (satellite) connect temporal behavior to physical processes studied by teams at Jet Propulsion Laboratory, Royal Observatory Edinburgh, and Smithsonian Astrophysical Observatory. High-energy gamma-ray detections from objects like Markarian 421 and Markarian 501 were obtained by instruments including VERITAS, MAGIC (telescope), HESS, and Fermi LAT. Radio interferometry with networks like Very Long Baseline Array and projects such as European VLBI Network resolve jets in sources linked to observatories including Green Bank Observatory and Arecibo Observatory.

Models describe a central supermassive black hole surrounded by an accretion disk informed by accretion theory developed in groups at Cambridge University, Yale University, and Columbia University, with a hot corona producing X-rays analogous to studies at Max Planck Institute for Radio Astronomy. The broad-line region and narrow-line region are mapped using spectroscopy from Large Binocular Telescope, Subaru Telescope, and Gemini Observatory; obscuring tori are probed by Very Large Telescope, Submillimeter Array, and mid-infrared instruments on Spitzer (spacecraft) and WISE. Relativistic jets are studied through polarization and imaging programs at NRAO, CERN-related collaborations, and institutes like Moscow State University and Korea Astronomy and Space Science Institute, and are linked to phenomena observed in Perseus Cluster, Fornax Cluster, and Coma Cluster.

Classification schemes—Seyfert galaxies, quasars, blazars, radio galaxies, LINERs—arose from observational taxonomies produced by teams at Mount Stromlo Observatory, Royal Greenwich Observatory, Australian National University, and consortia behind Hobby-Eberly Telescope and Sloan Digital Sky Survey. Notable examples include Seyfert 1, Seyfert 2, Flat-spectrum radio quasar, BL Lacertae, and classes distinguished in catalogs compiled by NASA/IPAC Extragalactic Database, SIMBAD, and researchers at Max Planck Society. Unification models proposed by groups at University of Oxford, Rutgers University, University of Toronto, and University of Edinburgh link orientation-dependent appearance to intrinsic structure; alternative schemes reference work at Leiden Observatory, Observatoire de Paris, Instituto de Astrofísica de Canarias, and National Astronomical Observatory of Japan.

The growth of supermassive black holes and their nuclei is studied in the context of galaxy assembly traced by surveys from Hubble Deep Field, COSMOS (survey), Great Observatories Origins Deep Survey, CANDELS, and simulations from teams at Princeton University, Harvard University, Los Alamos National Laboratory, Lawrence Berkeley National Laboratory, and Max Planck Institute for Astrophysics. Models incorporate feedback processes explored in projects at Stanford University, Massachusetts Institute of Technology, Imperial College London, and ETH Zurich, and connect to hierarchical formation frameworks associated with Lambda-CDM cosmology debates advanced by researchers at University of California, Santa Cruz, University of Pennsylvania, and University College London. Observational constraints on growth epochs use data from Sloan Digital Sky Survey, Keck Observatory, and Gemini Observatory to identify high-redshift quasars discovered by teams at University of Arizona, Carnegie Institution for Science, and University of Hawai'i.

Feedback effects such as quasar-mode and radio-mode outflows are studied in clusters and environments like Virgo Cluster, Virgo Supercluster, Local Group, Sloan Great Wall, and Bullet Cluster using X-ray and radio data from Chandra X-ray Observatory, XMM-Newton, and ALMA. Coevolution links between nuclei and host bulges are quantified through scaling relations such as the M–sigma relation investigated by researchers at Johns Hopkins University, University of California, Berkeley, University of Michigan, and Ohio State University. Large-scale surveys including Dark Energy Survey, Euclid (spacecraft), Large Synoptic Survey Telescope (now Vera C. Rubin Observatory), and WFIRST mission teams evaluate the role of active nuclei in reionization epochs probed by Planck (spacecraft) and WMAP analyses. Feedback signatures are compared across environments studied by groups at National Radio Astronomy Observatory, Space Telescope Science Institute, Canadian Space Agency, and Max Planck Institute for Extraterrestrial Physics.

Category:Astronomical objects