Dark Energy (DE) accounts for 74% of the mass-energy of the universe, dominates its present expansion, and determines its ultimate fate. Understanding DE may be the most important problem in fundamental physics today. To constrain the nature of DE, the best complement to CMBR data would be a measurement of the Hubble constant to better than 3%. The best prospect for measuring Ho to such high precision involves direct geometric distance measurements to circumnuclear water masers in galaxies in the Hubble flow, 50-200 Mpc distant. The Megamaser Cosmology Project (MCP) is an ambitious project to measure Ho directly with 3% precision by discovering and measuring suitable megamasers. Another important result from the MCP is the measurement of precise masses of the central black holes (BH) in megamaser disk galaxies. We measure the rotation of gas directly on sub-parsec scales, within the gravitational sphere of influence of the BH. We use the GBT, VLBA, VLA, and Effelsberg radio telescopes to conduct the necessary observations.
Main Results of MCP to Date
We have so far measured H0 = 68.6 +/- 5.5 km/s/Mpc based on maser distances to UGC 3789 (Reid et al. 2013) and NGC 6264 (Kuo et al. 2013). When we include preliminary results from additional galaxies, we determine H0 = 69.0 +/- 3.8 km/s/Mpc.
We have measured "gold standard" masses for supermassive black holes in 17 galaxies.
Mapped the pc-scale maser disks in NGC 2273, Mrk 1419, NGC 1194, NGC 4388, NGC 6323 and NGC 6264 (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 72 galaxies, 44% of all known extragalactic water masers. see the spectra