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

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

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.

Citation

He, Q., Li, R., Frenk, C. S., Nightingale, J., Cole, S., Amorisco, N. C., Massey, R., Robertson, A., Etherington, A., Amvrosiadis, A., & Cao, X. (2022). Galaxy–galaxy strong lens perturbations: line-of-sight haloes versus lens subhaloes. Monthly Notices of the Royal Astronomical Society, 512(4), 5862-5873. https://doi.org/10.1093/mnras/stac759

• Journal Article Type: Article
• Acceptance Date: Mar 11, 2022
• Online Publication Date: Mar 21, 2022
• Publication Date: 2022-06
• Deposit Date: Jul 12, 2022
• Publicly Available Date: Jul 12, 2022
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Royal Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 512
• Issue: 4
• Pages: 5862-5873
• DOI: https://doi.org/10.1093/mnras/stac759
• Public URL: https://durham-repository.worktribe.com/output/1198803