Measuring the Hubble Constant
A new geometric maser distance has been estimated to the active galaxy NGC 4258 from 18 epochs of Very Long Baseline Interferometry observations, and 10 years monitoring the velocities of the 22 GHz masers in NGC 4258, including GBT and VLA. A new model includes both disk warping and confocal elliptical maser orbits with differential precession. The distance to NGC 4258 is determined to be 7.60 ± 0.17 ± 0.15 Mpc, a 3% uncertainty including formal fitting and systematic terms. The resulting Hubble Constant, based on the use of the Cepheid variables in NGC 4258 to recalibrate the Cepheid distance scale, is H0 = 72.0 ± 3.0 km s-1 Mpc-1.
Figure: Covariance plot of Ho and w from the NGC 4258 maser observations.
View Publication: Toward a New Geometric Distance to the Active Galaxy NGC 4258. III. Final Results and the Hubble Constant, Liz Humphreys (ESO, CfA), Mark Reid (CfA), Jim Moran (CfA), Lincoln Greenhill (CfA), and Alice Argon (CfA), 2013 ApJ, 775, 13 (1 September 2013).
Added 21 Jan 2014
