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Measuring the Hubble constant with observations of water-vapor megamasers

Published online by Cambridge University Press:  26 February 2013

James Braatz ,
Mark Reid ,
Cheng-Yu Kuo ,
Violette Impellizzeri ,
James Condon ,
Christian Henkel ,
K. Y. Lo ,
Jenny Greene ,
Feng Gao  and
Wei Zhao
James Braatz
Affiliation:
National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
Mark Reid
Affiliation:
Harvard–Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138USA
Cheng-Yu Kuo
Affiliation:
Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 106, Taiwan
Violette Impellizzeri
Affiliation:
National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
James Condon
Affiliation:
National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
Christian Henkel
Affiliation:
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany Astronomy Department, King Abdulaziz University, P. O. Box 80203, Jeddah, Saudi Arabia
K. Y. Lo
Affiliation:
National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
Jenny Greene
Affiliation:
Department of Astrophysics, Princeton University, Princeton, NJ 08544, USA
Feng Gao
Affiliation:
National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA Shanghai Astronomical Observatory, Chinese Academy of Sciences, 200030 Shanghai, China
Wei Zhao
Affiliation:
National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA Shanghai Astronomical Observatory, Chinese Academy of Sciences, 200030 Shanghai, China
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Abstract

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To constrain models of dark energy, a precise measurement of the Hubble constant, H0, provides a powerful complement to observations of the cosmic microwave background. Recent, precise measurements of H0 have been based on the ‘extragalactic distance ladder,’ primarily using observations of Cepheid variables and Type Ia supernovae as standard candles. In the past, these methods have been limited by systematic errors, so independent methods of measuring H0 are of high value. Direct geometric distance measurements to circumnuclear H2O megamasers in the Hubble flow provide a promising new method to determine H0. The Megamaser Cosmology Project (MCP) is a systematic effort to discover suitable H2O megamasers and determine their distances, with the aim of measuring H0 to a few percent. Based on observations of megamasers in UGC 3789 and NGC 6264, and preliminary results from Mrk 1419, the MCP has so far measured H0 = 68.0 ± 4.8 km s−1 Mpc−1. This measurement will improve as distances to additional galaxies are incorporated. With the Green Bank Telescope, we recently discovered three more excellent candidates for distance measurements, and we are currently acquiring data to measure their distances.

Keywords

masersdistance scale
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 8 , Symposium S289: Advancing the Physics of Cosmic Distances , August 2012 , pp. 255 - 261
Copyright
Copyright © International Astronomical Union 2013

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