The Hubble–Lemaître constant and sound horizon from low-redshift probes

We revisit the claimed tension, or lack thereof, of measured values of the Hubble–Lemaître parameter H0 from cosmic microwave background (CMB) data and low-redshift indicators. Baryon acoustic oscillations (BAOs) rely on the scale of the sound horizon at recombination rs to convert angular measurements into angular-diameter distances, so fixing rs from CMB measurements already constrains H0. If departures from concordance cosmology are to be constrained, truly independent measurements of H0 are needed. We use the angular-diameter distances to three time-delay lenses from the H0LiCOW collaboration to calibrate the distance ladder, combine them with relative distances from supernovae ia and BAOs, leaving rs completely free, and provide the inferred coefficients (q0, j0, s0) in the polynomial expansion of H(z). We obtain H0rs = (9895 ± 161) km s−1 and H0 = (72 ± 7) km s−1 Mpc−1. Combined with H0 from H0LiCOW, then rs = (137 ± 4.5) Mpc is consistent with previous work and systematically lower than the CMB-inferred value. Our results are independent of the adopted cosmology, and removing supernovae with z < 0.1 has a negligible effect.