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 = 67.6 ± 4.0 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 in progress, and we expect to achieve a 4% or better measurement of H0 when the project is completed in 2017. Our measurement so far is
consistent with 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 mildly in tension with recent measurements based on standard candles
(H0 = 74 ± 2.5 km/s/Mpc).
We have mapped maser disks in 19 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 80 galaxies, which is half of all known extragalactic water masers. see the spectra
Here is a GBT spectrum of the remarkable maser in NGC 5765b: