Cosmography with Supernova Refsdal through time-delay cluster lensing: independent measurements of the Hubble constant and geometry of the Universe

TL;DR

This study uses strong lensing and time delays from SN Refsdal in galaxy cluster MACS J1149.5+2223 to independently measure key cosmological parameters, providing robust results without relying on other probes.

Contribution

It demonstrates that time-delay measurements in galaxy cluster lensing can independently constrain the Hubble constant and dark energy parameters, offering a new cosmological tool.

Findings

Measured H_0 = 65.1^{+3.5}_{-3.4} km/s/Mpc

Estimated dark energy density A0.76^{+0.15}_{-0.10}

Derived dark energy equation-of-state w = -0.92^{+0.15}_{-0.21}

Abstract

We present new measurements of the values of the Hubble constant, matter density, dark energy density, and dark energy density equation-of-state parameters from a full strong lensing analysis of the observed positions of 89 multiple images and 4 measured time delays of SN Refsdal multiple images in the Hubble Frontier Fields galaxy cluster MACS J1149.5+2223. By strictly following the identical modelling methodology as in our previous work, that was done before the time delays were available, our cosmographic measurements here are essentially blind based on the frozen procedure. Without using any priors from other cosmological experiments, in an open $w$CDM cosmological model, through our reference cluster mass model, we measure the following values: $H_0 = 65.1^{+3.5}_{-3.4}$ km s$^{-1}$ Mpc$^{-1}$, $\Omega_{\rm DE}=0.76^{+0.15}_{-0.10}$, and $w=-0.92^{+0.15}_{-0.21}$ (at the 68.3% confidence level). No other single cosmological probe is able to measure simultaneously all these parameters. Remarkably, our estimated values of the cosmological parameters, particularly $H_0$, are very robust and do not depend significantly on the assumed cosmological model and the cluster mass modelling details. The latter introduce systematic uncertainties on the values of $H_0$ and $w$ which are found largely subdominant compared to the statistical errors. The results of this study show that time delays in lens galaxy clusters, combined with extensive photometric and spectroscopic information, offers a novel and competitive cosmological tool.