Can third- and fourth-order multipoles plus radial variation of iso-density ellipses explain the observed flux ratios in B1422+231? YES, and a lesson learned from a TNG100 lensing galaxy sample
Abstract
Flux ratio anomalies in multiply-imaged quasar lenses are a long-standing issue. Using a classical system B1422+231 as a case study, we investigate how typical non-clumpy perturbations beyond elliptical shapes -- multipoles m3, m4 and radial variations in q, ϕq -- can account for the observed image positions and flux ratios under different observational precisions. We extract these perturbations from a pre-selected strong-lensing galaxy sample from the TNG100 simulation. Smooth macroscopic models (SIE+γ, EPL+γ) are then fitted to the observed image positions alone and to both positions and flux ratios, with and without including the extracted perturbations. With astrometric uncertainty of σp=10 mas, both macro-models alone can already successfully fit image positions within 3σp. At σp=2 mas, however, 'astrometric anomalies' appear if smooth macro-models alone are adopted. In this case, adding the extracted perturbations can explain the anomalous image positions. When both positions and flux ratios are adopted, the SIE+γ model family already shows 'flux ratio anomalies' at photometric uncertainty σf ≤ 10% (keeping σp=10 mas). When EPL+γ is used, the smooth model alone can simultaneously fit both positions and flux ratios with σf=10%, 5%, but not with σf=2%, where 'flux ratio anomalies' appear. Adding all four types of extracted perturbations can rescue the macro-models and explain the observed anomalous flux ratios. We present important lessons learned regarding model flexibility and degeneracy.
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BibTeX
@misc{feng2026third,
title = {{Can third- and fourth-order multipoles plus radial variation of iso-density ellipses explain the observed flux ratios in B1422$+$231? YES, and a lesson learned from a TNG100 lensing galaxy sample}},
author = {Ruizhe Feng and Dandan Xu and Dominique Sluse and Giulia Despali and Anowar Shajib and Cai-Na Hao},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2607.11559},
eprint = {2607.11559},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.11559},
}
RIS
TY - UNPB
TI - Can third- and fourth-order multipoles plus radial variation of iso-density ellipses explain the observed flux ratios in B1422+231? YES, and a lesson learned from a TNG100 lensing galaxy sample
AU - Ruizhe Feng
AU - Dandan Xu
AU - Dominique Sluse
AU - Giulia Despali
AU - Anowar Shajib
AU - Cai-Na Hao
PY - 2026
DA - 2026/10/12
PB - arXiv
DO - 10.48550/arxiv.2607.11559
UR - https://arxiv.org/abs/2607.11559
AB - Flux ratio anomalies in multiply-imaged quasar lenses are a long-standing issue. Using a classical system B1422+231 as a case study, we investigate how typical non-clumpy perturbations beyond elliptical shapes -- multipoles m_3, m_4 and radial variations in q, ϕ_q -- can account for the observed image positions and flux ratios under different observational precisions. We extract these perturbations from a pre-selected strong-lensing galaxy sample from the TNG100 simulation. Smooth macroscopic models (SIE+γ, EPL+γ) are then fitted to the observed image positions alone and to both positions and flux ratios, with and without including the extracted perturbations. With astrometric uncertainty of σ_p=10 mas, both macro-models alone can already successfully fit image positions within 3σ_p. At σ_p=2 mas, however, 'astrometric anomalies' appear if smooth macro-models alone are adopted. In this case, adding the extracted perturbations can explain the anomalous image positions. When both positions and flux ratios are adopted, the SIE+γ model family already shows 'flux ratio anomalies' at photometric uncertainty σ_f ≤ 10% (keeping σ_p=10 mas). When EPL+γ is used, the smooth model alone can simultaneously fit both positions and flux ratios with σ_f=10%, 5%, but not with σ_f=2%, where 'flux ratio anomalies' appear. Adding all four types of extracted perturbations can rescue the macro-models and explain the observed anomalous flux ratios. We present important lessons learned regarding model flexibility and degeneracy.
ER -