Issue |
A&A
Volume 667, November 2022
|
|
---|---|---|
Article Number | A123 | |
Number of page(s) | 33 | |
Section | Cosmology (including clusters of galaxies) | |
DOI | https://doi.org/10.1051/0004-6361/202243401 | |
Published online | 15 November 2022 |
TDCOSMO
IX. Systematic comparison between lens modelling software programs: Time-delay prediction for WGD 2038−4008
1
Department of Astronomy & Astrophysics, University of Chicago, Chicago, IL 60637, USA
e-mail: ajshajib@uchicago.edu
2
Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637, USA
3
Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA
4
National Astronomical Observatory of Japan (NAOJ), National Institutes of Natural Sciences, 2-21 Osawa, Mitaka, Tokyo 181-8588, Japan
5
Kavli IPMU (WPI), UTIAS, The University of Tokyo, Kashiwa, Chiba 277-8583, Japan
6
Kavli Institute for Particle Astrophysics and Cosmology and Department of Physics, Stanford University, Stanford, CA 94305, USA
7
SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
8
Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str. 1, 85748 Garching, Germany
9
Technische Universität München, Physik-Department, James-Franck-Str. 1, 85748 Garching, Germany
10
Institute of Astronomy and Astrophysics, Academia Sinica, 11F of ASMAB, No. 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan
11
Fermi National Accelerator Laboratory, PO Box 500 Batavia, IL 60510, USA
12
Department of Astronomy, University of California, Berkeley, 501 Campbell Hall, Berkeley, CA 94720, USA
13
DARK, Niels Bohr Institute, Jagtvej 128, 2200 Copenhagen, Denmark
14
Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
15
Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
16
Institute of Physics, Laboratoire d’Astrophysique, École Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, 1290 Versoix, Switzerland
17
STAR Institute, Quartier Agora, Allée du Six Août, 19c, 4000 Liege, Belgium
Received:
23
February
2022
Accepted:
2
September
2022
The importance of alternative methods for measuring the Hubble constant, such as time-delay cosmography, is highlighted by the recent Hubble tension. It is paramount to thoroughly investigate and rule out systematic biases in all measurement methods before we can accept new physics as the source of this tension. In this study, we perform a check for systematic biases in the lens modelling procedure of time-delay cosmography by comparing independent and blind time-delay predictions of the system WGD 2038−4008 from two teams using two different software programs: GLEE and LENSTRONOMY. The predicted time delays from the two teams incorporate the stellar kinematics of the deflector and the external convergence from line-of-sight structures. The un-blinded time-delay predictions from the two teams agree within 1.2σ, implying that once the time delay is measured the inferred Hubble constant will also be mutually consistent. However, there is a ∼4σ discrepancy between the power-law model slope and external shear, which is a significant discrepancy at the level of lens models before the stellar kinematics and the external convergence are incorporated. We identify the difference in the reconstructed point spread function (PSF) to be the source of this discrepancy. When the same reconstructed PSF was used by both teams, we achieved excellent agreement, within ∼0.6σ, indicating that potential systematics stemming from source reconstruction algorithms and investigator choices are well under control. We recommend that future studies supersample the PSF as needed and marginalize over multiple algorithms or realizations for the PSF reconstruction to mitigate the systematics associated with the PSF. A future study will measure the time delays of the system WGD 2038−4008 and infer the Hubble constant based on our mass models.
Key words: gravitational lensing: strong / methods: data analysis / galaxies: elliptical and lenticular / cD / distance scale
© A. J. Shajib et al. 2022
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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