A measurement of the hubble constant by the megamaser cosmology project

James Braatz, James Condon, Christian Henkel, Jenny Greene, Fred Lo, Mark Reid, Dominic Pesce, Feng Gao, Violette Impellizzeri, Cheng Yu Kuo, Wei Zhao, Anca Constantin, Lei Hao, Eugenia Litzinger

Research output: Contribution to journalArticlepeer-review

5 Scopus citations


The Megamaser Cosmology Project (MCP) measures the Hubble Constant by determining geometric distances to circumnuclear 22 GHz H2O megamasers in galaxies at low redshift (z < 0.05) but well into the Hubble flow. In combination with the recent, exquisite observations of the Cosmic Microwave Background by WMAP and Planck, these measurements provide a direct test of the standard cosmological model and constrain the equation of state of dark energy. The MCP is a multi-year project that has recently completed observations and is currently working on final analysis. Based on distance measurements to the first four published megamasers in the sample, the MCP currently determines H0 = 69.3 ± 4.2 km s-1 Mpc-1. The project is finalizing analysis for five additional galaxies. When complete, we expect to achieve a ~4% measurement. Given the tension between the Planck prediction of H0 in the context of the standard cosmological model and astrophysical measurements based on standard candles, the MCP provides a critical and independent geometric measurement that does not rely on external calibrations or a distance ladder.

Original languageEnglish (US)
Pages (from-to)86-91
Number of pages6
JournalProceedings of the International Astronomical Union
Issue numberS336
StatePublished - 2017

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • distance scale
  • masers


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