21cm Absorption by Compact Hydrogen Disks Around Black Holes in Radio-Loud Nuclei of Galaxies
arXiv:0802.2717 · doi:10.1088/1475-7516/2008/05/008
Abstract
The clumpy maser disks observed in some galactic nuclei mark the outskirts of the accretion disk that fuels the central black hole and provide a potential site of nuclear star formation. Unfortunately, most of the gas in maser disks is currently not being probed; large maser gains favor paths that are characterized by a small velocity gradient and require rare edge-on orientations of the disk. Here we propose a method for mapping the atomic hydrogen distribution in nuclear disks through its 21cm absorption against the radio continuum glow around the central black hole. In NGC 4258, the 21cm optical depth may approach unity for high angular-resolution (VLBI) imaging of coherent clumps which are dominated by thermal broadening and have the column density inferred from X-ray absorption data, ~10^{23}/cm^2. Spreading the 21cm absorption over the full rotation velocity width of the material in front of the narrow radio jets gives a mean optical depth of ~0.1. Spectroscopic searches for the 21cm absorption feature in other galaxies can be used to identify the large population of inclined gaseous disks which are not masing in our direction. Follow-up imaging of 21cm silhouettes of accelerating clumps within these disks can in turn be used to measure cosmological distances.
arXiv comment4 pages
References in corpus (26)
- The Stellar Cusp Around the Supermassive Black Hole in the Galactic Center
- Selfgravity and QSO disks
- Stellar disk in the galactic center -- a remnant of a dense accretion disk?
- A Method for Separating the Physics from the Astrophysics of High-Redshift 21cm Fluctuations
- Supermassive Stars in Quasar Disks
- The Geometry of and Mass Accretion Rate through the Maser Accretion Disk in NGC 4258
- Observations of HI Absorbing Gas in Compact Radio Sources at Cosmological Redshifts
- The Nuclear Regions of the Seyfert Galaxy NGC 4151 - Parsec-scale HI Absorption and a Remarkable Radio Jet
- The Discovery of H2O Maser Emission in Seven AGN and at High Velocities in the Circinus Galaxy
- Obscuration of the Parsec Scale Jets in the Compact Symmetric Object 1946+708
- The Link between Warm Molecular Disks in Maser Nuclei and Star Formation near the Black Hole at the Galactic Center
- Toward a New Distance to the Active Galaxy NGC 4258: II. Centripetal Accelerations and Investigation of Spiral Structure
- Extragalactic H_2O masers and X-ray absorbing column densities
- Discovery of Water Maser Emission in Eight AGN with 70-m Antennas of NASA's Deep Space Network
- Doppler-Shift Asymmetry in High-Velocity Maser Emission from Shocks in Circumnuclear Disks
- Discovery of Water Maser Emission in Five AGN and a Possible Correlation Between Water Maser and Nuclear 2-10 keV Luminosities
- 21 cm Absorption Studies with the Square Kilometer Array
- Limits on Dust in Rich Clusters of Galaxies from the Color of Background Quasars
- Redshifts and Neutral Hydrogen Observations of Compact Symmetric Objects in the COINS Sample
- X-ray Luminosity and Absorption Column Fluctuations in the H2O Maser Galaxy NGC 4258 from Weeks to Years
- X-ray Emission from Megamaser Galaxy IC 2560
- Disks, Tori, and Cocoons: Emission and Absorption Diagnostics of AGN Environments
- Extragalactic Water Masers, Geometric Estimation of H_o and Characterization of Dark Energy
- HI Absorption in the Gigamaser Galaxy TXS 2226-184 and the Relation between HI Absorption and Water Emission
- Exploring the Nucleus of the Gigamaser Galaxy TXS 2226-184
- A Thin HI Circumnuclear Disk in NGC4261