Toward a New Geometric Distance to the Active Galaxy NGC 4258. Iii. Final Results and the Hubble Constant

We report a new geometric maser distance estimate to the active galaxy NGC 4258. The data for the new model are maser line-of-sight (LOS) velocities and sky positions from 18 epochs of very long baseline interferometry observations, and LOS accelerations measured from a 10 yr monitoring program of the 22 GHz maser emission of NGC 4258. The new model includes both disk warping and confocal elliptical maser orbits with differential precession. The distance to NGC 4258 is \\ (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\\).