Year: 2026
Type: preprint
Abstract: The distribution of matter along the same line of sight but external to the main lens, quantified by $κ_\mathrm{ext}$, is a key source of uncertainty in time delay cosmography and other applications of strong lensing, and must be independently estimated to avoid biasing the inferred value of the Hubble constant ($H_0$). We present advancements and standardisations in the weighted number counts techniques used to constrain $κ_\mathrm{ext}$, in particular the use of the Euclid Flagship Simulation and a breakdown of the line-of-sight contributions between the observer, lens and source. As part of the TDCOSMO 2026 milestone analysis, we apply this updated method to the sample of 11 time delay lenses used in that study. Our estimates for certain systems are sensitive to these methodological changes, but are nonetheless consistent within $1σ$ for all but one of the systems which had been studied previously, with the median $κ_\mathrm{ext}$ across those systems changing from $-0.002$ to $-0.006$ following this new analysis. This work represents the first estimate of $κ_\mathrm{ext}$ values which includes the contribution of the observer-lens and lens-source terms, and largest standardised analysis of time delay lens environments to date.
Source: arXiv (Cornell University)
Institutions: Centre National de la Recherche Scientifique, Université de Montpellier, Laboratoire Univers et Particules de Montpellier, University of California, Los Angeles, University of California, Davis, Argonne National Laboratory, Max Planck Institute for Astrophysics, Technical University of Munich, University of Geneva
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, Agence Nationale de la Recherche, Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, Generalitat de Catalunya, Centre National de la Recherche Scientifique, Institut de Física d'Altes Energies, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, Agencia Estatal de Investigación
Awards: G1175115578, G1272927172, G2064873908, G2262748287, G2462415295, G2469010403, G2988934680, G3005324705, G300979063, G34346518, G3480869486, G3546882995, G425668148, G4430097687, G4526231891, Cosmology with all the lenses in Euclid: measuring Dark Energy and galaxy evolution with strong gravitational lensing, G5080475149, Einstein Lensing Rings to Observe the Non-baryonic matter Distribution, G5922099756, G6027777510, G6344031981, G69051668, G7080048889, G7084143925
OpenAlex ID: W7212287092