The Megamaser Cosmology Project (MCP)


Project Overview

The Megamaser Cosmology Project (MCP) is an NRAO Key Science Project to measure the Hubble Constant, H0, by determining geometric distances to circumnuclear 22 GHz H2O megamasers in galaxies well into the Hubble flow. In combination with the recent, exquisite observations of the Cosmic Microwave Background (CMB) 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 has so far determined H0 = 69.3 4.2 km/s/Mpc from published observations of UGC 3789 (Reid et al. 2013), NGC 6264 (Kuo et al. 2013), NGC 6323 (Kuo et al. 2015) and NGC 5765b (Gao et al. 2015).Work on other galaxies is in progress, and we expect to achieve a 4% or better measurement of H0 when the project is completed around the end of 2017. Our measurement so far is intermediate between the Planck prediction of H0 in the context of the standard cosmological model (H0 = 67.8 0.9 km/s/Mpc; Ade et al. 2015) and recent measurements based on standard candles (H0 = 74 2.5 km/s/Mpc).

Main Results of MCP to Date

  • We have so far measured H0 = 69.3 +/- 4.2 km/s/Mpc based on maser distances to UGC 3789 (Reid et al. 2013), NGC 6264 (Kuo et al. 2013), NGC 6323Kuo et al. 2015, and NGC 5765b Gao et al. 2016. In this combined estimate for H0, we apply an update to the modeling of UGC 3789 (more MCMC trials leading to convergence) that measured H0 = 76 +/- 8 km/s/Mpc for that one galaxy.
  • We have mapped maser disks in 20 galaxies and measured "gold standard" masses for their supermassive black holes, e.g. (Kuo et al. 2011).
  • The maser disks we mapped produce precise BH masses in relatively low-mass systems, where BH masses have been difficult to measure. Nearly all of the maser-based masses fall below the M-sigma relation defined by elliptical galaxies and have important implications for galactic evolution and BH feedback. (e.g. Greene et al. 2010)
  • The MCP and its pilot programs have discovered masers in 85 galaxies, about half of all known extragalactic water masers. see the spectra

  • Here is a GBT spectrum of the remarkable maser in NGC 5765b:

Team Members

  • Jim Braatz (NRAO)
  • Jim Condon (NRAO)
  • Anca Constantin (JMU)
  • Feng Gao (SHAO)
  • Jenny Greene (Princeton)
  • Lei Hao (SHAO)
  • Christian Henkel (MPIfR)
  • Violetta Impellizzeri (NRAO/JAO)
  • Cheng-Yu Kuo (NSYSU)
  • Eugenia Litzinger (Wurzburg)
  • Fred Lo (NRAO)
  • Dom Pesce (UVa)
  • Mark Reid (CfA)
  • Jan Wagner (KIAA)
  • Wei Zhao (SHAO)

Project Description


Internal Resources

-- JimBraatz
Topic revision: r56 - 2017-09-03, JimBraatz

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