We present an expanded sample of 75 Milky Way Cepheids with Hubble Space Telescope (HST) photometry and Gaia EDR3 parallaxes, which we use to recalibrate the extragalactic distance ladder and refine the determination of the Hubble constant. All HST observations were obtained with the same instrument (WFC3) and filters (F555W, F814W, F160W) used for imaging of extragalactic Cepheids in Type Ia supernova (SN Ia) hosts. The HST observations used the WFC3 spatial scanning mode to mitigate saturation and reduce pixel-to-pixel calibration errors, reaching a mean photometric error of 5 millimags per observation. We use new Gaia EDR3 parallaxes, greatly improved since DR2, and the period–luminosity (P–L) relation of these Cepheids to simultaneously calibrate the extragalactic distance ladder and to refine the determination of the Gaia EDR3 parallax offset. The resulting geometric calibration of Cepheid luminosities has 1.0% precision, better than any alternative geometric anchor. Applied to the calibration of SNe Ia, it results in a measurement of the Hubble constant of 73.0 1.4 km s⁻¹ Mpc⁻¹, in good agreement with conclusions based on earlier Gaia data releases. We also find the slope of the Cepheid P–L relation in the Milky Way, and the metallicity dependence of its zero-point, to be in good agreement with the mean values derived from other galaxies. In combination with the best complementary sources of Cepheid calibration, we reach 1.8% precision and find H ₀ = 73.2 1.3 km s⁻¹ Mpc⁻¹, a 4.2σ difference with the prediction from Planck CMB observations under ΛCDM. We expect to reach ∼1.3% precision in the near term from an expanded sample of ∼40 SNe Ia in Cepheid hosts.

我们用哈勃太空望远镜（ HST ）展示了75个银河系造父变星的扩展样本光度法和盖亚EDR3视差，我们用它们来重新校准银河外距离阶梯并完善哈勃常数的确定。所有HST观测都是使用用于成像Ia型超新星（SN Ia）宿主中银河外造父变星的同一台仪器（WFC3）和滤镜（F555W，F814W，F160W）获得的。HST观测使用WFC3空间扫描模式来减轻饱和度并减少像素到像素的校准误差，从而使每个观测的平均光度误差达到5毫米。我们使用了新的Gaia EDR3视差，自DR2以来已大大改善，并且使用这些造父变星的周期-光度（P-L）关系来同时校准银河外距离阶梯并完善Gaia EDR3视差偏移的确定。造父变星发光度的几何校准精度为1.0％，比任何其他几何锚都要好。应用于SNe Ia的校准后，哈勃常数的测量结果为73.0 1.4 km s^-1 Mpc ^-1，与基于早期Gaia数据发布的结论高度吻合。我们还发现，造父变星在银河系中的P–L关系的斜率及其零点对金属的依赖性与其他星系的平均值非常吻合。与造父校准的最佳互补源的组合，我们达到1.8％的精度和找到ħ ₀ = 73.21.3公里小号^-1 Mpc的^-1，4.2 σ与来自ΛCDM下普朗克CMB观测预测差。我们预计，从造父变星宿主中扩展的约40个SNe Ia样本，可以在短期内达到约1.3％的精度。