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.
