TDCOSMO XXXI: New techniques in line-of-sight studies of time delay lenses
Abstract
The distribution of matter along the same line of sight but external to the main lens, quantified by κext, 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 (H0). We present advancements and standardisations in the weighted number counts techniques used to constrain κext, 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 κext across those systems changing from −0.002 to −0.006 following this new analysis. This work represents the first estimate of κext values which includes the contribution of the observer-lens and lens-source terms, and largest standardised analysis of time delay lens environments to date.
Related
- TDCOSMO XXIX: JWST/NIRSpec IFU Spatially Resolved Kinematics of Three Time-delay Lenses
- TDCOSMO XXX: Spatially resolved kinematics of the deflectors in time-delay lens systems B1608+656 and SDSSJ1206+4332 from JWST-NIRSpec observation
- TDCOSMO XXVIII. The Hubble constant from the quadruply lensed quasar J1537−3010 with precise time delays
- TDCOSMO. XXVII. JWST-based Lens Models and H0 Measurement of WFI2033, HE0435, and PG1115
- TDCOSMO 2026: new insights on the Hubble tension from strong lensing time delays
BibTeX
@misc{johnson2026tdcosmo,
title = {{TDCOSMO XXXI: New techniques in line-of-sight studies of time delay lenses}},
author = {Daniel Johnson and Devon Williams and Chris Fassnacht and Patrick Wells and Pierre Fleury and Allan Schweinfurth and Martin Millon and Aymeric Galan},
howpublished = {HAL},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.11652},
eprint = {2609.11652},
archivePrefix = {arXiv},
url = {https://hal.science/hal-05759907v1},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - TDCOSMO XXXI: New techniques in line-of-sight studies of time delay lenses
AU - Daniel Johnson
AU - Devon Williams
AU - Chris Fassnacht
AU - Patrick Wells
AU - Pierre Fleury
AU - Allan Schweinfurth
AU - Martin Millon
AU - Aymeric Galan
PY - 2026
DA - 2026/09/10
PB - HAL
DO - 10.48550/arxiv.2609.11652
UR - https://hal.science/hal-05759907v1
AB - The distribution of matter along the same line of sight but external to the main lens, quantified by κ_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_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_ext across those systems changing from −0.002 to −0.006 following this new analysis. This work represents the first estimate of κ_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.
ER -