Galaxy mass modelling from multiwavelength JWST strong lens analysis: dark matter substructure, angular mass complexity, or both?
Samuel C. Lange, Aristeidis Amvrosiadis, J.W Nightingale, Qiuhan He, Carlos S. Frenk, Andrew Robertson, Shaun Cole, R. Massey, Xiaoyue Cao, Ran Li, Kaihao Wang
Abstract
ABSTRACT We analyse two galaxy-scale strong gravitational lenses, SPT0418-47 and SPT2147-50, using JWST NIRCam imaging across multiple filters. To account for angular complexity in the lens mass distribution, we introduce multipole perturbations with orders $m=1, 3, 4$. Our results show strong evidence for angular mass complexity in SPT2147, with multipole strengths of 0.3–1.7 per cent for $m=3, 4$ and 2.4–9.5 per cent for $m=1$, while SPT0418 shows no such preference. We also test lens models that include a dark matter substructure, finding a strong preference for a substructure in SPT2147-50 with a Bayes factor of $\Delta {\rm log}( { { {\varepsilon }}})$$\sim 60$ when multipoles are not included. Including multipoles reduces the Bayes factor to $\Delta {\rm log}( { { {\varepsilon }}})$$\sim 11$, still corresponding to a $5\sigma$ detection of a subhalo with an NFW (Navarro–Frenk–White) mass of $\log _{10}(M_{200}/{\rm M}_{\odot }) = 10.87^{+0.53}_{-0.71}$. While SPT2147-50 may represent the fourth detection of a dark matter substructure in a strong lens, further analysis is needed to confirm that the signal is not due to systematics associated with the lens mass model.