A tale of two double quasars: Hubble constant tension or biases?

Abstract

For a flat ΛCDM (standard) cosmology, a small sample of gravitationally lensed quasarswith measured time delays has recently provided a value of the Hubble constantH0intension with thePlanckflat ΛCDM result. Trying to check if this tension is real or not, weused basic observational constraints for two double quasars of the GLENDAMA sample (SBS 0909+532 and SDSS J1339+1310) to discuss the underlying value of H0 in a stan-dard cosmology. For SBS 0909+532, we were not able to obtain a reliable measurement ofH0. However, the current data of SDSS J1339+1310 are consistent with H0 around 67.8 km s−1Mpc−1andσ(H0)/H0∼10%. Although the formal uncertainty is still largeand mainly due to the lack of details on the mass density profile of the main lens galaxy,the central value ofH0coincides with that of the TDCOSMO+SLACS collaboration(using gravitational lens systems) and is within the 1σinterval fromPlanckcosmic mi-crowave background data. After getting these preliminary encouraging results throughonly one double quasar, we are currently planning to use several GLENDAMA systemsto accurately measure the Hubble constant and put constraints on other cosmologicalparameters.