http://arxiv.org/abs/2202.11101
The importance of alternative methods to measure 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 both teams incorporate the stellar kinematics of the deflector and the external convergence from line-of-sight structures. The unblinded time-delay predictions from the two teams agree within $1.2\sigma$ implying that once the time delay is measured the inferred Hubble constant will also be mutually consistent. However, there is a $\sim$4$\sigma$ discrepancy between the power-law model slope and external shear, which is a significant discrepancy at the level of lens models before incorporating the stellar kinematics and the external convergence. We identify the difference in the reconstructed point spread function (PSF) to be the source of this discrepancy. If the same reconstructed PSF is used by both teams, then we achieve excellent agreement within $\sim$0.6$\sigma$, indicating that potential systematics stemming from source reconstruction algorithms and investigator choices are well under control. We recommend future studies to supersample the PSF as needed and marginalize over multiple algorithms/realizations for the PSF reconstruction to mitigate the systematic associated with the PSF. A future study will measure the time delays of the system WGD 2038$-$4008 and infer the Hubble constant based on our mass models.
A. Shajib, K. Wong, S. Birrer, et. al.
Thu, 24 Feb 22
36/52
Comments: 35 pages, 26 figures, 4 tables. Submitted to A&A
You must be logged in to post a comment.