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Title: THE MEGAMASER COSMOLOGY PROJECT. II. THE ANGULAR-DIAMETER DISTANCE TO UGC 3789

Abstract

The Megamaser Cosmology Project (MCP) aims to determine H {sub 0} by measuring angular-diameter distances to galaxies in the Hubble flow using observations of water vapor megamasers in the circumnuclear accretion disks of active galaxies. The technique is based only on geometry and determines H {sub 0} in one step, independent of standard candles and the extragalactic distance ladder. In Paper I, we presented a very long baseline interferometry map of the maser emission from the Seyfert 2 galaxy UGC 3789. The map reveals an edge-on, sub-parsec disk in Keplerian rotation, analogous to the megamaser disk in NGC 4258. Here, we present 3.2 years of monthly Green Bank Telescope observations of the megamaser disk in UGC 3789. We use these observations to measure the centripetal accelerations of both the systemic and high-velocity maser components. The measured accelerations suggest that maser emission lines near the systemic velocity originate on the front side of the accretion disk, primarily from segments of two narrow rings. Adopting a two-ring model for the systemic features, we determine the angular-diameter distance to UGC 3789 to be 49.9 {+-} 7.0 Mpc. This is the most accurate geometric distance to a galaxy in the Hubble flow yet obtained.more » Based on this distance, we determine H {sub 0} = 69 {+-} 11 km s{sup -1} Mpc{sup -1}. We also measure the mass of the central black hole to be 1.09 x 10{sup 7} M{sub sun} {+-}14%. With additional observations, the uncertainty in the distance to this galaxy can be reduced to under 10%. Observations of megamaser disks in other galaxies will further reduce the uncertainty in H {sub 0} as measured by the MCP.« less

Authors:
; ;  [1]; ;  [2];  [3]
  1. National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States)
  2. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
  3. Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, D-53121 Bonn (Germany)
Publication Date:
OSTI Identifier:
21455105
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 718; Journal Issue: 2; Other Information: DOI: 10.1088/0004-637X/718/2/657; Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; BLACK HOLES; COSMOLOGY; EMISSION; GALAXIES; GALAXY NUCLEI; INTERFEROMETRY; MASS; RED SHIFT; ROTATION; TELESCOPES; VELOCITY; WATER VAPOR; FLUIDS; GASES; MOTION; VAPORS

Citation Formats

Braatz, J A, Condon, J J, Lo, K Y, Reid, M J, Humphreys, E M. L., and Henkel, C. THE MEGAMASER COSMOLOGY PROJECT. II. THE ANGULAR-DIAMETER DISTANCE TO UGC 3789. United States: N. p., 2010. Web. doi:10.1088/0004-637X/718/2/657.
Braatz, J A, Condon, J J, Lo, K Y, Reid, M J, Humphreys, E M. L., & Henkel, C. THE MEGAMASER COSMOLOGY PROJECT. II. THE ANGULAR-DIAMETER DISTANCE TO UGC 3789. United States. https://doi.org/10.1088/0004-637X/718/2/657
Braatz, J A, Condon, J J, Lo, K Y, Reid, M J, Humphreys, E M. L., and Henkel, C. 2010. "THE MEGAMASER COSMOLOGY PROJECT. II. THE ANGULAR-DIAMETER DISTANCE TO UGC 3789". United States. https://doi.org/10.1088/0004-637X/718/2/657.
@article{osti_21455105,
title = {THE MEGAMASER COSMOLOGY PROJECT. II. THE ANGULAR-DIAMETER DISTANCE TO UGC 3789},
author = {Braatz, J A and Condon, J J and Lo, K Y and Reid, M J and Humphreys, E M. L. and Henkel, C},
abstractNote = {The Megamaser Cosmology Project (MCP) aims to determine H {sub 0} by measuring angular-diameter distances to galaxies in the Hubble flow using observations of water vapor megamasers in the circumnuclear accretion disks of active galaxies. The technique is based only on geometry and determines H {sub 0} in one step, independent of standard candles and the extragalactic distance ladder. In Paper I, we presented a very long baseline interferometry map of the maser emission from the Seyfert 2 galaxy UGC 3789. The map reveals an edge-on, sub-parsec disk in Keplerian rotation, analogous to the megamaser disk in NGC 4258. Here, we present 3.2 years of monthly Green Bank Telescope observations of the megamaser disk in UGC 3789. We use these observations to measure the centripetal accelerations of both the systemic and high-velocity maser components. The measured accelerations suggest that maser emission lines near the systemic velocity originate on the front side of the accretion disk, primarily from segments of two narrow rings. Adopting a two-ring model for the systemic features, we determine the angular-diameter distance to UGC 3789 to be 49.9 {+-} 7.0 Mpc. This is the most accurate geometric distance to a galaxy in the Hubble flow yet obtained. Based on this distance, we determine H {sub 0} = 69 {+-} 11 km s{sup -1} Mpc{sup -1}. We also measure the mass of the central black hole to be 1.09 x 10{sup 7} M{sub sun} {+-}14%. With additional observations, the uncertainty in the distance to this galaxy can be reduced to under 10%. Observations of megamaser disks in other galaxies will further reduce the uncertainty in H {sub 0} as measured by the MCP.},
doi = {10.1088/0004-637X/718/2/657},
url = {https://www.osti.gov/biblio/21455105}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 718,
place = {United States},
year = {Sun Aug 01 00:00:00 EDT 2010},
month = {Sun Aug 01 00:00:00 EDT 2010}
}