An Independent Measurement of H0 from Lensed Quasars

Strong gravitational lens systems with time delays between the multiple images are a powerful probe of cosmology, particularly of the Hubble constant ($H_{0}$) that is key to probing dark energy, neutrino physics, and the spatial curvature of the Universe, as well as discovering new physics. The $H_{0}$ Lenses In COSMOGRAIL’s Wellspring (H0LiCOW) project has measured $H_{0}$ from lensed quasars using deep Hubble Space Telescope and AO imaging, precise time delay measurements from the COSMOGRAIL monitoring project, a measurement of the velocity dispersion of the lens galaxies, and a characterization of the mass distribution along the line of sight. Our latest results from a total of six lenses constrains H0 to be $73.3_{-1.8}^{+1.7}$ km/s/Mpc for a flat Lambda CDM cosmology, which is a measurement to 2.4% precision. These results are consistent with independent determinations of $H_{0}$ using type Ia supernovae calibrated by the distance ladder method, and are in 3.1$\sigma$ tension with the results of Planck CMB measurements. Combined with the latest distance ladder results from the SH0ES project, we find a 5.3$\sigma$ tension between Planck and late-Universe probes, hinting at possible new physics beyond the standard LCDM model and highlighting the importance of this independent probe.