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Arxiv: Galaxy Mass Modelling from Multi-Wavelength JWST Strong Lens Analysis: Dark Matter Substructure, Angular Mass Complexity, or Both? Published: 10/16/2024 10:32:47 PM Updated: 10/16/2024 10:32:47 PM

Paper abstract: We analyze two galaxy-scale strong gravitational lenses, SPT0418-47 andSPT2147-50, using JWST NIRCam imaging across multiple filters. To account forangular complexity in the lens mass distribution, we introduce multipoleperturbations with orders m=1, 3, 4. Our results show strong evidence forangular mass complexity in SPT2147, with multipole strengths of 0.3-1.7 \%for m=3, 4 and 2.4-9.5 \% for m=1, while SPT0418 shows no suchpreference. We also test lens models that include a dark matter substructure,finding a strong preference for a substructure in SPT2147-50 with a Bayesfactor (log-evidence change) of ~ 60 when multipoles are not included.Including multipoles reduces the Bayes factor to ~ 11, still correspondingto a 5\sigma detection of a subhalo with an NFW mass of\log_{10}(M_{200}/M_{\odot}) = 10.87\substack{+0.53\\ -0.71}. WhileSPT2147-50 may represent the fourth detection of a dark matter substructure ina strong lens, further analysis is needed to confirm that the signal is not dueto systematics associated with the lens mass model.