The 1% Concordance Hubble Constant

TL;DR

This paper analyzes the tension between different measurements of the Hubble constant, finding they are consistent within statistical expectations and determining a combined value of 69.6 km/s/Mpc with 1% precision, showing no evidence for new physics.

Contribution

It provides a comprehensive analysis of the consistency between CMB, BAO, and distance ladder measurements, and combines them to refine the Hubble constant estimate.

Findings

Measurements are consistent within statistical expectations.

Best-fit Hubble constant is 69.6+/-0.7 km/s/Mpc.

No evidence for physics beyond the standard cosmological model.

Abstract

The determination of the Hubble constant has been a central goal in observational astrophysics for nearly 100 years. Extraordinary progress has occurred in recent years on two fronts: the cosmic distance ladder measurements at low redshift and cosmic microwave background (CMB) measurements at high redshift. The CMB is used to predict the current expansion rate through a best-fit cosmological model. Complementary progress has been made with baryon acoustic oscillation (BAO) measurements at relatively low redshifts. While BAO data do not independently determine a Hubble constant, they are important for constraints on possible solutions and checks on cosmic consistency. A precise determination of the Hubble constant is of great value, but it is more important to compare the high and low redshift measurements to test our cosmological model. Significant tension would suggest either uncertainties not accounted for in the experimental estimates, or the discovery of new physics beyond the standard model of cosmology. In this paper we examine in detail the tension between the CMB, BAO, and cosmic distance ladder data sets. We find that these measurements are consistent within reasonable statistical expectations, and we combine them to determine a best-fit Hubble constant of 69.6+/-0.7 km/s/Mpc. This value is based upon WMAP9+SPT+ACT+6dFGS+BOSS/DR11+H_0/Riess; we explore alternate data combinations in the text. The combined data constrain the Hubble constant to 1%, with no compelling evidence for new physics.