Volume 643, November 2020
|Number of page(s)||40|
|Section||Cosmology (including clusters of galaxies)|
|Published online||20 November 2020|
IV. Hierarchical time-delay cosmography – joint inference of the Hubble constant and galaxy density profiles⋆
Kavli Institute for Particle Astrophysics and Cosmology and Department of Physics, Stanford University, Stanford, CA 94305, USA
2 Physics and Astronomy Department, University of California, Los Angeles, CA 90095, USA
3 Institute of Physics, Laboratory of Astrophysics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, 1290 Versoix, Switzerland
4 DARK, Niels-Bohr Institute, Lyngbyvej 2, 2100 Copenhagen, Denmark
5 Institute of Astrononmy, University of Cambridge, Madingley Road, Cambridge CB30HA, UK
6 Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB30HA, UK
7 Physics Dept., University of California, Davis, 1 Shields Ave., Davis, CA 95616, USA
8 Institute of Cosmology and Gravitation, University of Portsmouth, Burnaby Rd, Portsmouth PO1 3FX, UK
9 Carnegie Visiting Scientist, USA
10 Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
11 National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan
12 STAR Institute, Quartier Agora, Allée du six Août, 19c, 4000 Liège, Belgium
13 Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
14 INAF, Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Naples, Italy
15 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching, Germany
16 Physik-Department, Technische Universität München, James-Franck-Straße 1, 85748 Garching, Germany
17 Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), 11F of ASMAB, No.1, Section 4, Roosevelt Road, Taipei 10617, Taiwan
18 Kavli IPMU (WPI), UTIAS, The University of Tokyo, Kashiwa, Chiba 277-8583, Japan
19 NSF’s National Optical-Infrared Astronomy Research Laboratory, 950 N. Cherry Ave., Tucson, AZ 85719, USA
20 University of Vienna, Department of Astrophysics, Türkenschanzstr. 17, 1180 Wien, Austria
21 Fermi National Accelerator Laboratory, PO Box 500, Batavia, IL 60510, USA
22 Kavli Institute for Cosmological Physics, Department of Astronomy & Astrophysics, The University of Chicago, Chicago, IL 60637, USA
23 Garching bei München, Munich 85748, Germany
Accepted: 11 October 2020
The H0LiCOW collaboration inferred via strong gravitational lensing time delays a Hubble constant value of H0 = 73.3−1.8+1.7 km s−1 Mpc−1, describing deflector mass density profiles by either a power-law or stars (constant mass-to-light ratio) plus standard dark matter halos. The mass-sheet transform (MST) that leaves the lensing observables unchanged is considered the dominant source of residual uncertainty in H0. We quantify any potential effect of the MST with a flexible family of mass models, which directly encodes it, and they are hence maximally degenerate with H0. Our calculation is based on a new hierarchical Bayesian approach in which the MST is only constrained by stellar kinematics. The approach is validated on mock lenses, which are generated from hydrodynamic simulations. We first applied the inference to the TDCOSMO sample of seven lenses, six of which are from H0LiCOW, and measured H0 = 74.5−6.1+5.6 km s−1 Mpc−1. Secondly, in order to further constrain the deflector mass density profiles, we added imaging and spectroscopy for a set of 33 strong gravitational lenses from the Sloan Lens ACS (SLACS) sample. For nine of the 33 SLAC lenses, we used resolved kinematics to constrain the stellar anisotropy. From the joint hierarchical analysis of the TDCOSMO+SLACS sample, we measured H0 = 67.4−3.2+4.1 km s−1 Mpc−1. This measurement assumes that the TDCOSMO and SLACS galaxies are drawn from the same parent population. The blind H0LiCOW, TDCOSMO-only and TDCOSMO+SLACS analyses are in mutual statistical agreement. The TDCOSMO+SLACS analysis prefers marginally shallower mass profiles than H0LiCOW or TDCOSMO-only. Without relying on the form of the mass density profile used by H0LiCOW, we achieve a ∼5% measurement of H0. While our new hierarchical analysis does not statistically invalidate the mass profile assumptions by H0LiCOW – and thus the H0 measurement relying on them – it demonstrates the importance of understanding the mass density profile of elliptical galaxies. The uncertainties on H0 derived in this paper can be reduced by physical or observational priors on the form of the mass profile, or by additional data.
Key words: gravitational lensing: strong / galaxies: general / galaxies: kinematics and dynamics / distance scale / cosmological parameters / cosmology: observations
The full analysis is available at https://github.com/TDCOSMO/hierarchy_analysis_2020_public.
© ESO 2020
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