We use cookies to ensure that we give you the best experience on our website. By continuing to browse this repository, you give consent for essential cookies to be used. You can read more about our Privacy and Cookie Policy.

Durham Research Online
You are in:

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.


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
Full text:(VoR) Version of Record
Download PDF
Publisher Web site:
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

Save or Share this output

Look up in GoogleScholar