Tight $H_0$ constraint from galaxy redshfit surveys: combining baryon acoustic osillation measurements and Alcock-Paczynski test

We report a tight Hubble constant constraint $67.78^{+1.21}_{-1.86}$ km s$^{-1}$ Mpc$^{-1}$ (2.26\% precision) derived from galaxy redshift surveys. We combine the BAO measurements from 6dFGS, the SDSS DR7 main galaxies, the BOSS DR12 galaxies, and eBOSS DR14 quasars, and also apply the tomographic Alcock-Paczynski (AP) method to the BOSS DR12 galaxies, to place constraints on $H_0$ in the spatially flat $\Lambda$CDM framework. Our result is fully consistent with the CMB constraints from Planck, but in $2.58\sigma$ tension with local measurements of Riess et al. 2016. Compared with the BAO alone constraint, the BAO+AP combined result reduces the error bar by 32%. This shows the strong power of the tomographic AP method in extracting cosmological information from galaxy redshift surveys.