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The Nature of Flat-Spectrum Nuclear Radio Emission in Seyfert Galaxies

Published online by Cambridge University Press:  13 May 2016

C. G. Mundell ,
A.S. Wilson ,
J.S. Ulvestad  and
A. L. Roy
C. G. Mundell
Affiliation:
ARI, Liverpool John Moores University, U.K. ([email protected]) University of Maryland, College Park, MD20742
A.S. Wilson
Affiliation:
University of Maryland, College Park, MD20742
J.S. Ulvestad
Affiliation:
NRAO, P.O. Box O, Socorro, NM87801
A. L. Roy
Affiliation:
NRAO, P.O. Box O, Socorro, NM87801 MPIfR, Bonn, Germany

Abstract

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Parsec-scale VLBA imaging of five Seyfert galaxies with flat-spectrum radio nuclei was conducted to determine whether the flat spectrum represents thermal emission from the accretion disk/obscuring torus or nonthermal, synchrotron self-absorbed emission. Four of the five show emission consistent with synchrotron self-absorption, with intrinsic sizes ∼0.05-0.2 pc (or 104 gravitational radii for a 108 M⊙ black hole for the smallest). In contrast, NGC 4388, which was detected with MERLIN but not the VLBA, shows thermal emission with similar properties to that detected in NGC 1068. It is notable that the two Seyfert galaxies with detected thermal nuclear radio emission both have large X-ray absorbing columns, suggesting that columns in excess of ∼1024 cm−2 are needed for such disks to be detectable.

Type
The Inner Regions of Galaxies
Information
Symposium - International Astronomical Union , Volume 205: Galaxies and their Constituents at the Highest Angular Resolutions , 2001 , pp. 72 - 73
Copyright
Copyright © Astronomical Society of the Pacific 2001 

References

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