• 2016. The American Astronomical Society. All rights reserved. We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%. The bulk of this improvement comes from new near-infrared (NIR) observations of Cepheid variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these in turn leverage the magnitude-redshift relation based on 300 SNe Ia at z < 0.15. All 19 hosts as well as the megamaser system NGC 4258 have been observed with WFC3 in the optical and NIR, thus nullifying cross-instrument zeropoint errors in the relative distance estimates from Cepheids. Other noteworthy improvements include a 33% reduction in the systematic uncertainty in the maser distance to NGC 4258, a larger sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW) Cepheids. We consider four geometric distance calibrations of Cepheids: (i) megamasers in NGC 4258, (ii) 8 DEBs in the LMC, (iii) 15 MW Cepheids with parallaxes measured with HST/FGS, HST/WFC3 spatial scanning and/or Hipparcos, and (iv) 2 DEBs in M31. The Hubble constant from each is 72.25, 2.51, 72.04,2.67, 76.18,2.37, and 74.50,3.27 km s-1 Mpc-1, respectively. Our best estimate of H 0 = 73.24, 1.74 km s-1 Mpc-1 combines the anchors NGC 4258, MW, and LMC, yielding a 2.4% determination (all quoted uncertainties include fully propagated statistical and systematic components). This value is 3.4 higher than 66.93, 0.62 km s-1 Mpc-1 predicted by CDM with 3 neutrino flavors having a mass of 0.06 eV and the new Planck data, but the discrepancy reduces to 2.1 relative to the prediction of 69.3, 0.7 km s-1 Mpc-1 based on the comparably precise combination of WMAP+ACT+SPT+BAO observations, suggesting that systematic uncertainties in CMB radiation measurements may play a role in the tension. If we take the conflict between Planck high-redshift measurements and our local determination of H 0 at face value, one plausible explanation could involve an additional source of dark radiation in the early universe in the range of N eff 0.4-1. We anticipate further significant improvements in H 0 from upcoming parallax measurements of long-period MW Cepheids.

published proceedings


altmetric score

  • 765.93

author list (cited authors)

  • Riess, A. G., Macri, L. M., Hoffmann, S. L., Scolnic, D., Casertano, S., Filippenko, A. V., ... Foley, R. J.

citation count

  • 1680

complete list of authors

  • Riess, Adam G||Macri, Lucas M||Hoffmann, Samantha L||Scolnic, Dan||Casertano, Stefano||Filippenko, Alexei V||Tucker, Brad E||Reid, Mark J||Jones, David O||Silverman, Jeffrey M||Chornock, Ryan||Challis, Peter||Yuan, Wenlong||Brown, Peter J||Foley, Ryan J

publication date

  • July 2016