M. J. Reid et al. 2009 ApJ 695 287 doi:10.1088/0004-637X/695/1/287
M. J. Reid1, J. A. Braatz2, J. J. Condon2, L. J. Greenhill1, C. Henkel3 and K. Y. Lo2
Show affiliationsThe Megamaser Cosmology Project (MCP) seeks to measure the Hubble Constant (H 0) in order to improve the extragalactic distance scale and constrain the nature of dark energy. We are searching for sources of H2O maser emission from active galactic nuclei with sub-pc accretion disks, as in NGC 4258, and following up these discoveries with very long baseline interferometric (VLBI) imaging and spectral monitoring. Here we present a VLBI map of the H2O masers toward UGC 3789, a galaxy well into the Hubble Flow. We have observed masers moving at rotational speeds up to 800 km s–1 at radii as small as 0.08 pc. Our map reveals masers in a nearly edge-on disk in Keplerian rotation about a 107 M ☉ supermassive black hole. When combined with centripetal accelerations, obtained by observing spectral drifts of maser features (to be presented in Paper II), the UGC 3789 masers may provide an accurate determination of H 0, independent of luminosities and metallicity and extinction corrections.
accretion, accretion disks; cosmology: observations; distance scale; galaxies: distances and redshifts; galaxies: individual (UGC 3789); masers
Issue 1 (2009 April 10)
Received 2008 November 21, accepted for publication 2009 January 13
Published 2009 March 30
M. J. Reid et al. 2009 ApJ 695 287
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