The Hubble Space Telescope Key Project on the Extragalactic Distance Scale. XXV. A recalibration of cepheid distances to Type Ia supernovae and the value of the hubble constant

Cepheid-based distances to seven Type Ia supernovae (SNe) host galaxies hav e been derived using the standard Hubble Space Telescope (HST) Key Project on the Extragalactic Distance Scale pipeline. For the first time, this allo ws for a transparent comparison of data accumulated as part of three differ ent HST projects: the Key Project, the Sandage et al. Type Ia supernovae (S Ne) program, and the Tanvir et al. Leo I Group study. Reanalyzing the Tanvi r et al. galaxy and six Sandage et al. galaxies, we find a mean (weighted) offset in true distance moduli of 0.12 +/- 0.07 mag; i.e., 6% in linear dis tance, in the sense of reducing the distance scale or increasing H-0. Adopt ing the reddening-corrected Hubble relations of Suntzeff et al. tied to a z ero point based on SNe 1990N, 1981B, 1998bu, 1989B, 1972E, and 1960F and th e photometric calibration of Hill et al. leads to a Hubble constant of H-0 = 68 +/- 2(random) +/- 5(systematic) km s(-1) Mpc(-1). Adopting the Kennicu tt et al. Cepheid period-luminosity-metallicity dependency decreases the in ferred H-0 by 4%. The H-0 result from Type Ia SNe is now in good agreement, to within their respective uncertainties, with that from the Tully-Fisher and surface brightness fluctuation relations.