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arXiv · 2110.04512

Galaxy-galaxy strong lens perturbations: line-of-sight haloes versus lens subhaloes

Qiuhan He·Ran Li·Carlos S. Frenk·James Nightingale·Shaun Cole·Nicola C. Amorisco·Richard Massey·Andrew Robertson·Amy Etherington·Aristeidis Amvrosiadis·Xiaoyue Cao
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Abstract

We rederive the number density of intervening line-of-sight haloes relative to lens subhaloes in galaxy-galaxy strong lensing observations, where these perturbers can generate detectable image fluctuations. Previous studies have calculated the detection limit of a line-of-sight small-mass dark halo by comparing the lensing deflection angles it would cause, to those caused by a subhalo within the lens. However, this overly simplifies the difference in observational consequences between a subhalo and a line-of-sight halo. Furthermore, it does not take into account degeneracies between an extra subhalo and the uncertain properties of the main lens. More in keeping with analyses of real-world observations, we regard a line-of-sight halo as detectable only if adding it to a smooth model generates a statistically significant improvement in the reconstructed image. We find that the number density of detectable line-of-sight perturbers has been overestimated by as much as a factor of two in the previous literature. For typical lensing geometries and configurations, very deep imaging is sensitive to twice as many line-of-sight perturbers as subhaloes, but moderate depth imaging is sensitive to only slightly more line-of-sight perturbers than subhaloes.

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Qiuhan He, Ran Li, Carlos S. Frenk, James Nightingale, Shaun Cole, Nicola C. Amorisco, Richard Massey, Andrew Robertson, Amy Etherington, Aristeidis Amvrosiadis, Xiaoyue Cao. 2021-10-09. Galaxy-galaxy strong lens perturbations: line-of-sight haloes versus lens subhaloes. https://doi.org/10.1093/mnras%2Fstac759

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