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Title:
Improved Constraints on the Gravitational Lens Q0957+561. I. Weak Lensing
Authors:
Nakajima, R.; Bernstein, G. M.; Fadely, R.; Keeton, C. R.; Schrabback, T.
Affiliation:
AA(Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USA ; Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA ), AB(Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USA ), AC(Department of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854, USA ), AD(Department of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854, USA ), AE(Argelander-Institut für Astronomie, Universität Bonn, D-53121 Bonn, Germany ; Leiden Observatory, Universiteit Leiden, NL-2333 CA Leiden, Netherlands)
Publication:
The Astrophysical Journal, Volume 697, Issue 2, pp. 1793-1804 (2009). (ApJ Homepage)
Publication Date:
06/2009
Origin:
IOP
ApJ Keywords:
galaxies: clusters: individual: Q0957+561, galaxies: halos, gravitational lensing
DOI:
10.1088/0004-637X/697/2/1793
Bibliographic Code:
2009ApJ...697.1793N

Abstract

Attempts to constrain the Hubble constant using the strong gravitational lens system Q0957+561 are limited by systematic uncertainties in the mass model, since the time delay is known very precisely. One important systematic effect is the mass-sheet degeneracy, which arises because strong lens modeling cannot constrain the presence or absence of a uniform mass sheet κ, which rescales H 0 by the factor (1 - κ). In this paper, we present new constraints on the mass sheet derived from a weak-lensing analysis of the Hubble Space Telescope imaging of a 6 arcmin square region surrounding the lensed quasar. The average mass sheet within a circular aperture (the strong lens model region) is constrained by integrating the tangential weak gravitational shear over the surrounding area. We find the average convergence within a 30'' radius around the lens galaxy to be κ(<30'') = 0.166 ± 0.056 (1σ confidence level), normalized to the quasar redshift. This includes contributions from both the lens galaxy and the surrounding cluster. We also constrain a few other low-order terms in the lens potential by applying a multipole aperture mass formalism to the gravitational shear in an annulus around the strong-lensing region. Implications for strong lens models and the Hubble constant are discussed in an accompanying paper.
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