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We present an expanded sample of 75 Milky Way Cepheids with Hubble SpaceTelescope (HST) photometry and Gaia EDR3 parallaxes which we use to recalibratethe extragalactic distance ladder and refine the determination of the Hubbleconstant. All HST observations were obtained with the same instrument (WFC3)and filters (F555W, F814W, F160W) used for imaging of extragalactic Cepheids inType Ia supernova (SN Ia) hosts. The HST observations used the WFC3 spatialscanning mode to mitigate saturation and reduce pixel-to-pixel calibrationerrors, reaching a mean photometric error of 5 millimags per observation. Weuse new Gaia EDR3 parallaxes, vastly improved since DR2, and thePeriod-Luminosity (PL) relation of these Cepheids to simultaneously calibratethe extragalactic distance ladder and to refine the determination of the GaiaEDR3 parallax offset. The resulting geometric calibration of Cepheidluminosities has 1.0% precision, better than any alternative geometric anchor.Applied to the calibration of SNe~Ia, it results in a measurement of the Hubbleconstant of 73.0 +/- 1.4 km/sec/Mpc, in good agreement with conclusions basedon earlier Gaia data releases. We also find the slope of the Cepheid PLrelation in the Milky Way, and the metallicity dependence of its zeropoint, tobe in good agreement with the mean values derived from other galaxies. Incombination with the best complementary sources of Cepheid calibration, wereach 1.8% precision and find H_0=73.2 +/- 1.3 km/sec/Mpc, a 4.2 sigmadifference with the prediction from Planck CMB observations under LambdaCDM. Weexpect to reach ~1.3% precision in the near term from an expanded sample of ~40SNe Ia in Cepheid hosts.

the astrophysical journal. letters

Cosmic Distances Calibrated to 1% Precision with Gaia EDR3 Parallaxes  and Hubble Space Telescope Photometry of 75 Milky Way Cepheids Confirm  Tension with LambdaCDM