TY - JOUR

T1 - IX. Systematic comparison between lens modelling software programs

T2 - Time-delay prediction for WGD 2038-4008

AU - Shajib, A. J.

AU - Wong, K. C.

AU - Birrer, S.

AU - Suyu, S. H.

AU - Treu, T.

AU - Buckley-Geer, E. J.

AU - Lin, H.

AU - Rusu, C. E.

AU - Poh, J.

AU - Palmese, A.

AU - Agnello, A.

AU - Auger-Williams, M. W.

AU - Galan, A.

AU - Schuldt, S.

AU - Sluse, D.

AU - Courbin, F.

AU - Frieman, J.

AU - Millon, M.

PY - 2022/11/15

Y1 - 2022/11/15

N2 - 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 1.2o-, implying that once the time delay is measured the inferred Hubble constant will also be mutually consistent. However, there is a similar to 4o-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 similar to 0.6o-, 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.

AB - 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 1.2o-, implying that once the time delay is measured the inferred Hubble constant will also be mutually consistent. However, there is a similar to 4o-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 similar to 0.6o-, 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.

KW - gravitational lensing

KW - strong - methods

KW - data analysis - galaxies

KW - elliptical and lenticular

KW - cD - distance scale

KW - EARLY-TYPE GALAXIES

KW - HUBBLE CONSTANT

KW - DARK-MATTER

KW - ACS SURVEY

KW - ELLIPTIC GALAXIES

KW - DENSITY PROFILE

KW - MASS

KW - COSMOGRAPHY

KW - H-0

KW - PRECISION

U2 - 10.1051/0004-6361/202243401

DO - 10.1051/0004-6361/202243401

M3 - Journal article

VL - 667

JO - Astronomy & Astrophysics

JF - Astronomy & Astrophysics

SN - 0004-6361

M1 - A123

ER -