Impact of Large-Scale Structure along Line-of-Sight on Time-Delay Cosmography

[2509.26382] Impact of Large-Scale Structure along Line-of-Sight on Time-Delay Cosmography Skip to main content Search Submit Donate Log in Astrophysics > Cosmology and Nongalactic Astrophysics arXiv:2509.26382 (astro-ph) [Submitted on 30 Sep 2025 ( v1 ), last revised 13 Sep 2026 (this version, v2)] Title: Impact of Large-Scale Structure along Line-of-Sight on Time-Delay Cosmography Authors: Shijie Lin , Bin Hu , Chengliang Wei , Guoliang Li , Yiping Shu , Xinzhong Er , Zuhui Fan View PDF HTML (experimental) Abstract: Time-delay cosmography offers a promising and independent method for measuring cosmological distances by monitoring multiple images of gravitationally lensed sources. However, beyond the main deflector, large-scale structure along the line-of-sight (LoS) also deflects travelling light rays via weak lensing (WL). Due to resolution limitations, accurately measuring WL on arcsecond scales remains highly challenging. In this work, we evaluate the LoS effects on both lensing images and time-delay measurements using a more straightforward, high-resolution N-body simulation that provides a more realistic matter distribution compared to the traditional, computationally cheaper halo rendering method. We employ the multi-plane ray tracing technique, which is traditionally utilised to compute WL effects at the arcminute scale, extending its application to the strong lensing regime at the arcsecond scale. We focus on quadruple-image systems and present the following findings: (1) In addition to a constant external convergence, large-scale structures within a region approximately 2 arcminutes in angular size act as external perturbers, inducing inhomogeneous fluctuations on the arcsecond scale. (2) Standard single-plane models suffer from severe geometric degeneracies between foreground shear and main lens ellipticity. By ignoring complex multi-plane couplings, these models fail to accurately recover the external convergence, producing broad, bimodal errors. (3) Explicitly accounting for the LoS shear via the minimal lens model successfully breaks these degeneracies, yielding robust and tightly constrained reconstructions. (4) Uncorrected foreground convergence introduces a $0.5\sim0.7\%$ systematic bias in time-delay distance estimation. Our findings highlight that advanced LoS modeling is indispensable for precision time-delay cosmography. Comments: Published on this http URL Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO) Cite as: arXiv:2509.26382 [astro-ph.CO] (or arXiv:2509.26382v2 [astro-ph.CO] for this version) https://doi.org/10.48550/arXiv.2509.26382 Focus to learn more arXiv-issued DOI via DataCite Journal reference: Astrophys.J.Suppl. 286 (2026) 1, 8 Related DOI : https://doi.org/10.3847/1538-4365/ae8538 Focus to learn more DOI(s) linking to related resources Submission history From: Shi-Jie Lin [ view email ] [v1] Tue, 30 Sep 2025 15:12:39 UTC (9,819 KB) [v2] Sun, 13 Sep 2026 08:50:49 UTC (9,437 KB) Full-text links: Access Paper: View PDF HTML (experimental) TeX Source view license Current browse context: astro-ph.CO < prev | next > new | recent | 2025-09 Change to browse by: astro-ph References & Citations INSPIRE HEP SciX Google Scholar Semantic Scholar export BibTeX citation Bookmark Bibliographic Tools Bibliographic and Citation Tools Bibliographic Explorer Toggle Bibliographic Explorer ( What is the Explorer? ) Connected Papers Toggle Connected Papers ( What is Connected Papers? ) Litmaps Toggle Litmaps ( What is Litmaps? ) scite.ai Toggle scite Smart Citations ( What are Smart Citations? ) Code, Data, Media Code, Data and Media Associated with this Article alphaXiv Toggle alphaXiv ( What is alphaXiv? ) Links to Code Toggle CatalyzeX Code Finder for Papers ( What is CatalyzeX? ) DagsHub Toggle DagsHub ( What is DagsHub? ) GotitPub Toggle Gotit.pub ( What is GotitPub? ) Huggingface Toggle Hugging Face ( What is Huggingface? ) ScienceCast Toggle ScienceCast ( What is ScienceCast? ) Demos Demos Replicate Toggle Replicate ( What is Replicate? ) Spaces Toggle Hugging Face Spaces ( What is Spaces? ) Spaces Toggle TXYZ.AI ( What is TXYZ.AI? ) Related Papers Recommenders and Search Tools Link to Influence Flower Influence Flower ( What are Influence Flowers? ) Core recommender toggle CORE Recommender ( What is CORE? ) IArxiv recommender toggle IArxiv Recommender ( What is IArxiv? ) Author Venue Institution Topic About arXivLabs arXivLabs: experimental projects with community collaborators arXivLabs is a framework that allows collaborators to develop and share new arXiv features directly on our website. 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