We present the direct measurement of the Hubble constant , yielding the direct measurement of the angular-diameter distance to NGC 6264 using the H _ { 2 } O megamaser technique .
Our measurement is based on sensitive observations of the circumnuclear megamaser disk from four observations with the Very Long Baseline Array , the Green Bank Telescope and the Effelsberg Telescope .
We also monitored the maser spectral profile for 2.3 years using the Green Bank Telescope to measure accelerations of maser lines by tracking their line-of-sight velocities as they change with time .
The measured accelerations suggest that the systemic maser spots have a significantly wider radial distribution than in the archetypal megamaser in NGC 4258 .
We model the maser emission as arising from a circumnuclear disk with orbits dominated by the central black hole .
The best fit of the data gives a Hubble constant of H _ { 0 } = 68 \pm 9 km s ^ { -1 } Mpc ^ { -1 } , which corresponds to an angular-diameter distance of 144 \pm 19 Mpc .
In addition , the fit also gives a mass of the central black hole of ( 3.09 \pm 0.42 ) \times 10 ^ { 7 } M _ { \odot } .
The result demonstrates the feasibility of measuring distances to galaxies located well into the Hubble flow by using circumnuclear megamaser disks .