SIMBAD references

NGC 4258 is a critical galaxy for establishing the extragalactic distance scale and estimating the Hubble constant (H₀). Water masers in the nucleus of the galaxy orbit about its supermassive black hole, and very long baseline interferometric observations of their positions, velocities, and accelerations can be modeled to give a geometric estimate of the angular-diameter distance to the galaxy. We have improved the technique to obtain model parameter values, reducing both statistical and systematic uncertainties compared to previous analyses. We find the distance to NGC 4258 to be 7.576 ± 0.082 (stat.) ± 0.076 (sys.) Mpc. Using this as the sole source of calibration of the Cepheid-SN Ia distance ladder results in H₀=72.0±1.9 km s^–1 Mpc^–1, and in concert with geometric distances from Milky Way parallaxes and detached eclipsing binaries in the LMC we find H₀=73.5±1.4 km s^–1 Mpc^–1. The improved distance to NGC 4258 also provides a new calibration of the tip of the red giant branch of M_F814W=-4.01±0.04 mag, with reduced systematic errors for the determination of H₀ compared to the LMC-based calibration, because it is measured on the same Hubble Space Telescope (HST) photometric system and through similarly low extinction as SN Ia host halos. The result is H₀=71.1±1.9 km s^–1 Mpc^–1, in good agreement with the result from the Cepheid route, and there is no difference in H₀ when using the same calibration from NGC 4258 and the same SN Ia Hubble diagram intercept to start and end both distance ladders.