Hubble constant and sound horizon from the late-time Universe

We measure the expansion rate of the recent Universe and the calibration scale of the baryon acoustic oscillation (BAO) from low-redshift data. BAO relies on the calibration scale, i.e., the sound horizon at the end of drag epoch $r_d$, which often imposes a prior of the cosmic microwave background (CMB) measurement from the Planck satellite. In order to make really independent measurements of $H_0$, we leave $r_d$ completely free and use the BAO data sets combined with the 31 observational $H(z)$ data, GW170817 and Pantheon sample of Type Ia supernovae. In $Λ$CDM model, we get $H_0=68.63^{+1.75}_{-1.77}$ km s$^{-1}$ Mpc$^{-1}$, $r_d=146.85^{+3.29}_{-3.77}$ Mpc. For the two model-independent reconstructions of $H(z)$, we obtain $H_0=68.02\pm1.82$ km s$^{-1}$ Mpc$^{-1}$, $r_d=148.18^{+3.36}_{-3.78}$ Mpc in the cubic expansion, and $H_0=68.58\pm1.76$ km s$^{-1}$ Mpc$^{-1}$, $r_d=148.02^{+3.63}_{-3.60}$ Mpc in the polynomial expansion. The values of Hubble constant $H_0$ and sound horizon $r_d$ are consistent with the estimate derived from the Planck CMB data assuming a flat $Λ$CDM model, but $H_0$ is in $2.4\sim2.6$ $σ$ tension with SH0ES 2019, respectively.

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