An Improved Distance to NGC 4258 and Its Implications for the Hubble Constant
Abstract
NGC 4258 is a critical galaxy for establishing the extragalactic distance scale and estimating the Hubble constant ({H}_{0}). 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 angulardiameter 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 CepheidSN Ia distance ladder results in {H}_{0}=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 {H}_{0}=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 {H}_{0} compared to the LMCbased 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 {H}_{0}=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 {H}_{0} when using the same calibration from NGC 4258 and the same SN Ia Hubble diagram intercept to start and end both distance ladders.
 Publication:

The Astrophysical Journal
 Pub Date:
 December 2019
 DOI:
 10.3847/20418213/ab552d
 arXiv:
 arXiv:1908.05625
 Bibcode:
 2019ApJ...886L..27R
 Keywords:

 Observational cosmology;
 Galaxy distances;
 1146;
 590;
 Astrophysics  Astrophysics of Galaxies;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 As will be published in ApJ (15 pages