Abstract
Strong gravitational lensing provides an independent measurement of the Hubble parameter (H _{0}). One remaining systematic is a bias from the additional mass due to a galaxy group at the lens redshift or along the sightline. We quantify this bias for more than 20 strong lenses that have wellsampled sightline mass distributions, focusing on the convergence κ and shear γ. In 23% of these fields, a lens group contributes ≥1% convergence bias; in 57%, there is a similarly significant lineofsight group. For the nine timedelay lens systems, H _{0} is overestimated by % on average when groups are ignored. In 67% of fields with total , lineofsight groups contribute more convergence than do lens groups, indicating that the lens group is not the only important mass. Lens environment affects the ratio of four (quad) to two (double) image systems; all seven quads have lens groups while only 3 of 10 doubles do, and the highest convergences due to lens groups are in quads. We calibrate the γκ relation: log(κ_{tot}) =(194 ±0.34)log (γ_{tot})+(1.31 ±0.49) with an rms scatter of 0.34 dex. Although shear can be measured directly from lensed images, unlike convergence, it can be a poor predictor of convergence; for 19% of our fields, κ is ≥2γ. Thus, accurate cosmology using strong gravitational lenses requires precise measurement and correction for all significant structures in each lens field.
Original language  English (US) 

Article number  94 
Journal  Astrophysical Journal 
Volume  850 
Issue number  1 
DOIs  
State  Published  Nov 20 2017 
Keywords
 galaxies: groups: general
 gravitational lensing: strong
ASJC Scopus subject areas
 Astronomy and Astrophysics
 Space and Planetary Science
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Spectroscopy of the fields of gravitational lenses
Wilson, M. L. (Creator), Zabludoff, A. I. (Creator), Keeton, C. R. (Creator), Wong, K. C. (Creator), Williams, K. A. (Creator), French, K. D. (Creator) & Momcheva, I. G. (Creator), Centre de Donnees Strasbourg (CDS), 2019
DOI: 10.26093/cds/vizier.18500094, https://cdsarc.cds.unistra.fr/vizbin/cat/J/ApJ/850/94
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