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A Supermassive Object in the Nucleus of NGC 4258?

Published online by Cambridge University Press:  30 March 2016

L.J. Greenhill ,
D.R. Jiang ,
J.M. Moran ,
M.J. Reid ,
K.-Y. Lo ,
M.J. Claussen ,
C. Henkel ,
T.L. Wilson ,
R. Becker  and
J.G.A. Wouterloot
L.J. Greenhill
Affiliation:
Harvard-Smithsonian Center for Astrophysics 60 Garden St, Cambridge, MA 02138USA
D.R. Jiang
Affiliation:
Harvard-Smithsonian Center for Astrophysics 60 Garden St, Cambridge, MA 02138USA
J.M. Moran
Affiliation:
Harvard-Smithsonian Center for Astrophysics 60 Garden St, Cambridge, MA 02138USA
M.J. Reid
Affiliation:
Harvard-Smithsonian Center for Astrophysics 60 Garden St, Cambridge, MA 02138USA
K.-Y. Lo
Affiliation:
Department of Astronomy, University of Illinois 1002W. Green St, Urbana, IL 61801USA
M.J. Claussen
Affiliation:
National Radio Astronomy Observatory P. O. Box O, Socorro, NM 87801USA
C. Henkel
Affiliation:
Max-Planck-Institut für Radioastronomie Auf dem Hugel 69, D-58121 Bonn, Germany
T.L. Wilson
Affiliation:
Max-Planck-Institut für Radioastronomie Auf dem Hugel 69, D-58121 Bonn, Germany
R. Becker
Affiliation:
GKSS Forschungszentrum, Institut für Physik Max-Planck-Strasse, D-21502 Geesthacht, Germany
J.G.A. Wouterloot
Affiliation:
I. Physikalisches Institut Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany

Abstract

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VLBI images of the H2O megamaser in NGC 4258 and a time series of spectra taken over several years combine to make a compelling case that there is a compact molecular disk associated with a supermassive object in the nucleus of this galaxy. The images of the maser in the velocity rangenear the systemic velocity show a highly elongated structure with a major axis of about 0.009 pc, along which the gradient in line-of-sight velocity is essentially a constant of 7970 ± 40 km s-1 pc-1. The observed acceleration of these spectral features by about 6-11 km s-1 yr-1, the presence of high-velocity maser satellite emission, and the VLBI results suggest emission from a disk of diameter0.2 pc, rotating with a velocity of ~800 Km s-1, bound by a mass of 1.5×107 M⊙ and denisty of ≳3.6×109 M⊙ pc-3

Type
II. Joint Discussions
Information
Highlights of Astronomy , Volume 10: Highlights of Astronomy. As presented at the XXIInd General Assembly of the IAU, 1994 , 1995 , pp. 531 - 534
Copyright
Copyright © Kluwer 1995

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