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., and Foley, Ryan J. 2016. "A 2.4% Determination of the Local Value of the Hubble Constant." The Astrophysical Journal, 826 56. https://doi.org/10.3847/0004-637X/826/1/56.
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
