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

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 d...

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Veröffentlicht in:Monthly notices of the Royal Astronomical Society 2022-04, Vol.512 (4), p.5862-5873
Hauptverfasser: He, Qiuhan, Li, Ran, Frenk, Carlos S, Nightingale, James, Cole, Shaun, Amorisco, Nicola C, Massey, Richard, Robertson, Andrew, Etherington, Amy, Amvrosiadis, Aristeidis, Cao, Xiaoyue
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Sprache:eng
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Zusammenfassung: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.
ISSN:0035-8711
1365-2966
DOI:10.1093/mnras/stac759