Narrowing down the Hubble constant value by exploiting the extended surface brightness of the supernova Refsdal host galaxy

Abstract

We present the first inference of the Hubble constant and matter density parameter from a strongly lensed supernova by exploiting the mass model of a galaxy cluster enhanced by an extended surface brightness reconstruction. Building upon the recent mass model of the galaxy cluster MACS J1149.5+2223, relying on the identified image positions only, we include the surface brightness distribution of the SN Refsdal host, to infer some cosmological parameter values within a flat LCDM framework. We consider two cosmological parameterizations, with either H0 and Ωm or H0 alone treated as free parameters, acknowledging the milder dependency on Ωm when incorporating additional constraints from the SN host. We explore four different mass-model realizations to assess some of the systematic uncertainties associated with the constraint weighting and source reconstruction. Although known as one of the main possible systematic effects, including influences from the external convergence, we deliberately keep the cluster total mass parametrization fixed to that of the previously published point-like mass model to enable a fair comparison. This reveals that incorporating 77,000 HST pixels reduces the uncertainty on the inferred value of the Hubble constant by a factor of 2.0, while all model realizations remain mutually consistent. Our final measurements are $H_0 = 65.0^{+2.0}_{-1.8}$ km/s/Mpc and $Ω_m = 0.30^{+0.08}_{-0.09}, in agreement with previous results. This corresponds to a substantially improved precision, reaching a remarkable 3.0% uncertainty on the value of H0 given our cluster total mass parameterization. The contributions of the uncertainties on the lens total mass and on the measured time delays to the final H0 error are now comparable, indicating that future improvements in cluster-scale time-delay cosmography will increasingly depend on (abridged version).