A Redetermination of the Hubble Constant with the Hubble Space Telescope from a Differential Distance Ladder

TL;DR

This work uses a homogeneous infrared Cepheid distance ladder anchored by the geometric maser distance to NGC 4258 to recalibrate Type Ia supernovae and determine the Hubble constant as $H_0=74.2\pm3.6$ km s$^{-1}$ Mpc$^{-1}$. By measuring 240 Cepheids with the same instrument and band across six SN host galaxies, the authors reduce systematic errors and leverage a reddening-free Wesenheit approach, yielding robust differential distances to SN hosts. The combined Cepheid–SN Ia analysis, when integrated with WMAP5 constraints, delivers $w=-1.12\pm0.12$, consistent with a cosmological constant and improving dark-energy inferences; future maser discoveries and Gaia parallaxes promise further reductions in $H_0$ and tighter $w(z)$ constraints. Overall, the study demonstrates that a carefully controlled, differential distance ladder can yield a precise local $H_0$ and contribute significantly to our understanding of dark energy.

Abstract

We report observations of 240 Cepheid variables obtained with the Near Infrared Camera (NICMOS) through the F160W filter on the Hubble Space Telescope (HST). The Cepheids are distributed across six recent hosts of Type Ia supernovae (SNe Ia) and the "maser galaxy" NGC 4258, allowing us to directly calibrate the peak luminosities of the SNe Ia from the precise, geometric distance measurements provided by the masers. New features of our measurement include the use of the same instrument for all Cepheid measurements across the distance ladder and homogeneity of the Cepheid periods and metallicities thus necessitating only a differential measurement of Cepheid fluxes and reducing the largest systematic uncertainties in the determination of the fiducial SN Ia luminosity. The NICMOS measurements reduce differential extinction in the host galaxies by a factor of 5 over past optical data. Combined with an expanded of 240 SNe Ia at z<0.1 which define their magnitude-redshift relation, we find H_0=74.2 +/-3.6, a 4.8% uncertainty including both statistical and systematic errors. We show that the factor of 2.2 improvement in the precision of H_0 is a significant aid to the determination of the equation-of-state of dark energy, w = P/(rho c^2). Combined with the WMAP 5-year measurement of Omega_M h^2, we find w= -1.12 +/- 0.12 independent of high-redshift SNe Ia or baryon acoustic oscillations (BAO). This result is also consistent with analyses based on the combination of high-z SNe Ia and BAO. The constraints on w(z) now with high-z SNe Ia and BAO are consistent with a cosmological constant and improved by a factor of 3 from the refinement in H_0 alone. We show future improvements in H_0 are likely and will further contribute to multi-technique studies of dark energy.