Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 512, Issue 4, Pages 5862-5873Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stac759
Keywords
gravitational lensing: strong; dark matter
Categories
Funding
- National Nature Science Foundation of China [11988101, 11773032, 12022306]
- China Manned Space Project [CMS-CSST-2021-B01, CMSCSST-2021-A01]
- K. C. Wong Education Foundation
- European Research Council (ERC) [GA 786910]
- Science and Technology Facilities Council (STFC) [ST/T000244/1]
- UKSA [ST/V001582/1, ST/T002565/1]
- Royal Society
- STFC/UKRI Ernest Rutherford Fellowship [ST/S004998/1]
- BEIS capital funding via STFC capital grants [ST/K00042X/1, ST/P002293/1, ST/R002371/1, ST/S002502/1]
- Durham University
- STFC [ST/R000832/1]
- ERC through Horizon2020 grant EWC [AMD-776247-6]
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This study rederives the relative number density between intervening line-of-sight haloes and lens subhaloes in galaxy-galaxy strong lensing observations, finding an overestimation of detectable line-of-sight perturbers in previous literature.
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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