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

He, Qiuhan and Li, Ran and Frenk, Carlos S and Nightingale, James and Cole, Shaun and Amorisco, Nicola C and Massey, Richard and Robertson, Andrew and Etherington, Amy and Amvrosiadis, Aristeidis and Cao, Xiaoyue (2022) 'Galaxy–galaxy strong lens perturbations: line-of-sight haloes versus lens subhaloes.', Monthly Notices of the Royal Astronomical Society, 512 (4). pp. 5862-5873.

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.

Item Type:Article
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1093/mnras/stac759
Publisher statement:This article has been accepted for publication in Monthly notices of the Royal Astronomical Society. ©: 2022 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:11 March 2022
Date deposited:12 July 2022
Date of first online publication:21 March 2022
Date first made open access:12 July 2022

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