Powerful Water Masers in Active Galactic Nuclei

Abstract

Luminous water maser emission in the 6_(16)-5_(23) line at 22 GHz has been detected from two dozen galaxies. In all cases the emission is confined to the nucleus and has been found only in AGN, in particular, in Type 2 Seyferts and LINERs. I argue that most of the observed megamaser sources are powered by X-ray irradiation of dense gas by the central engine. After briefly reviewing the physics of these X-Ray Dissociation Regions, I discuss in detail the observations of the maser disk in NGC 4258, its implications, and compare alternative models for the maser emission. I then discuss the observations of the other sources that have been imaged with VLBI to date, and how they do or do not fit into the framework of a thin, rotating disk, as in NGC 4258. Finally, I briefly discuss future prospects, especially the possibility of detecting other water maser transitions.

45 pages, 16 figures. Refereed and greatly expanded version of my review talk at the ASA meeting in Lorne, July 2001. To appear in Proceedings of the Astronomical Society of Australia

References in corpus (6)

• Jet- and Wind-Driven Ionized Outflows in the Superbubble and Star-Forming Disk of NGC 3079
• The Nature of the Nuclear H2O Masers of NGC 1068: Reverberation and Evidence for a Rotating Disk Geometry
• A revised Cepheid distance to NGC 4258 and a test of the distance scale
• The BeppoSAX view of the X-ray active nucleus of NGC4258
• Ultra-High-Density Molecular Core and Warped Nuclear Disk in the Deep Potential of Radio-Lobe Galaxy NGC 3079
• MERLIN imaging of the maser flare in Markarian 348

Cited by in corpus (27)

• The Link between Warm Molecular Disks in Maser Nuclei and Star Formation near the Black Hole at the Galactic Center
• Extragalactic H_2O masers and X-ray absorbing column densities
• New H2O masers in Seyfert and FIR bright galaxies
• A Green Bank Telescope Search for Water Masers in Nearby Active Galactic Nuclei
• Probing the Magnetic Field at Sub-Parsec Radii in the Accretion Disk of NGC 4258
• A new analysis of the nucleus of NGC 1068 with MIDI observations
• The Mass of Quasar Broad Emission Line Regions
• Extremely Luminous Water Vapor Emission from a Type 2 Quasar at Redshift z = 0.66
• Positional Coincidence of H2O Maser and a Plasma Obscuring Torus in Radio Galaxy NGC 1052
• First Detection of Millimeter/Submillimeter Extragalactic H2O Maser Emission
• X-ray versus Optical Observations of Active Galactic Nuclei: Evidence for Large Grains?
• A Scaling Relation Between Megamaser Disk Radius and Black Hole Mass in Active Galactic Nuclei
• Disks, Tori, and Cocoons: Emission and Absorption Diagnostics of AGN Environments
• The torquing of circumnuclear accretion disks by stars and the evolution of massive black holes
• Accretion disk warping by resonant relaxation: The case of maser disk NGC4258
• Scintillation in the Circinus Galaxy water megamasers
• On the X-ray Properties of OH Megamaser Sources: Chandra Snapshot Observations
• Water megamaser emission in hard X-ray selected AGN
• Second Epoch ALMA Observations of 321 GHz Water Maser Emission in NGC 4945 and the Circinus Galaxy
• ALMA detection of millimetre 183 GHz H2O maser emission in the Superantennae galaxy at z ~ 0.06
• H${}_2$O Maser Pumping: The Effect of Quasi-Resonance Energy Transfer in Collisions between H${}_2$ and H${}_2$O Molecules
• ALMA Sub-arcsec-resolution 183 GHz H2O and Dense Molecular Line Observations of Nearby Ultraluminous Infrared Galaxies
• The Origin of Parsec-Scale Gaseous and Stellar Disks in the Galactic Center and AGNs
• Very Long Baseline Interferometry imaging of H2O maser emission in the nearby radio galaxy NGC 4261
• H_2O maser and a plasma obscuring torus in the radio galaxy NGC 1052
• Searching Water Megamasers By Using Mid-infrared Spectroscopy (I): Possible Mid-infrared Indicators
• The Origin of Keplerian Megamaser Disks