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The Sub-Parsec Structure of Accretion Disks as Revealed by VLBI Imaging of Free-Free Absorption

Published online by Cambridge University Press:  13 May 2016

D.L. Jones ,
A.E. Wehrle ,
B.G. Piner  and
D.L. Meier
D.L. Jones
Affiliation:
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
A.E. Wehrle
Affiliation:
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
B.G. Piner
Affiliation:
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
D.L. Meier
Affiliation:
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA

Abstract

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The physical conditions in the inner parsec of accretion disks believed to orbit the central black holes in active galactic nuclei can be probed by imaging the absorption of background radio emission by ionized gas in the disk. High angular resolution radio observations of several nearby galaxies at multiple frequencies have revealed evidence for free-free absorption by disks or tori of ionized gas. The depth and angular width of the absorption increases with decreasing frequency. The longest possible baselines are needed to provide adequate angular resolution at low frequencies where the effects of free-free absorption are most evident. Recent results from VSOP as well as ground-based VLBI observations of the nearby galaxy NGC 4261 illustrate the critical importance of high angular resolution at frequencies below 10 GHz.

Type
The Inner Regions of Galaxies
Information
Symposium - International Astronomical Union , Volume 205: Galaxies and their Constituents at the Highest Angular Resolutions , 2001 , pp. 44 - 47
Copyright
Copyright © Astronomical Society of the Pacific 2001 

References

Jones, D.L. & Wehrle, A.E. 1997, ApJ, 484, 186.Google Scholar
Jones, D.L., Wehrle, A.E., Meier, D.L., & Piner, B.G. 2000, ApJ, 534, 165.CrossRefGoogle Scholar
Piner, B.G., Jones, D.L., & Wehrle, A.E. 2000, in preparation.Google Scholar