Measuring the Value of the Hubble Constant "à la Refsdal"

C. Grillo, P. Rosati, S. H. Suyu, I. Balestra, G. B. Caminha, A. Halkola, P. L. Kelly, M. Lombardi, A. Mercurio, S. A. Rodney, T. Treu

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Realizing Refsdal's original idea from 1964, we present estimates of the Hubble constant that are complementary to, and potentially competitive with, those of other cosmological probes. We use the observed positions of 89 multiple images, with extensive spectroscopic information, from 28 background sources and the measured time delays between the images S1-S4 and SX of supernova "Refsdal" (z = 1.489), which were obtained thanks to Hubble Space Telescope deep imaging and Multi Unit Spectroscopic Explorer data. We extend the strong-lensing modeling of the Hubble Frontier Fields galaxy cluster MACS J1149.5+2223 (z = 0.542), published by Grillo et al. (2016), and explore different ΛCDM models. Taking advantage of the lensing information associated to the presence of very close pairs of multiple images at various redshifts, and to the extended surface brightness distribution of the SN Refsdal host, we can reconstruct the total mass-density profile of the cluster very precisely. The combined dependence of the multiple-image positions and time delays on the cosmological parameters allows us to infer the values of H 0 and Ωm with relative (1σ) statistical errors of, respectively, 6% (7%) and 31% (26%) in flat (general) cosmological models, assuming a conservative 3% uncertainty on the final time delay of image SX and, remarkably, no priors from other cosmological experiments. Our best estimate of H 0, based on the model described in this work, will be presented when the final time-delay measurement becomes available. Our results show that it is possible to utilize time delays in lens galaxy clusters as an important alternative tool for measuring the expansion rate and the geometry of the universe.

Original languageEnglish (US)
Article number94
JournalAstrophysical Journal
Issue number2
StatePublished - Jun 20 2018

Bibliographical note

Funding Information:
C.G. acknowledges support by VILLUM FONDEN Young Investigator Programme through grant no.10123. S.H.S. thanks the Max Planck Society for support through the Max Planck Research Group. T.T. acknowledges support by the Packard Foundation through a Packard Research Fellowship and by NASA through grant HST-GO-14199. This work is based in large part on data collected in service mode at ESO VLT, through the Director’s Discretionary Time Programme 294.A-5032. The CLASH Multi-Cycle Treasury Program is based on observations made with the NASA/ESA Hubble Space Telescope. The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. ACS was developed under NASA Contract NAS 5-32864.

Publisher Copyright:
© 2018. The American Astronomical Society. All rights reserved..


  • cosmological parameters
  • dark energy
  • dark matter
  • distance scale
  • galaxies: clusters: individual (MACS J1149.5+2223)
  • gravitational lensing: strong


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