Dissecting the Gravitational Lens B1608+656. I. Lens Potential Reconstruction

Creators: Suyu, S. H.; Marshall, P. J.; Blandford, R. D.; Fassnacht, C. D.; Koopmans, L. V. E.; McKean, J. P.; Treu, T.

Abstract

Strong gravitational lensing is a powerful technique for probing galaxy mass distributions and for measuring cosmological parameters. Lens systems with extended source-intensity distributions are particularly useful for this purpose since they provide additional constraints on the lens potential (mass distribution). We present a pixelated approach to modeling the lens potential and source-intensity distribution simultaneously. The method makes iterative and perturbative corrections to an initial potential model. For systems with sources of sufficient extent such that the separate lensed images are connected by intensity measurements, the accuracy in the reconstructed potential is solely limited by the quality of the data. We apply this potential reconstruction technique to deep Hubble Space Telescope observations of B1608+656, a four-image gravitational lens system formed by a pair of interacting lens galaxies. We present a comprehensive Bayesian analysis of the system that takes into account the extended source-intensity distribution, dust extinction, and the interacting lens galaxies. Our approach allows us to compare various models of the components of the lens system, which include the point-spread function (PSF), dust, lens galaxy light, source-intensity distribution, and lens potential. Using optimal combinations of the PSF, dust, and lens galaxy light models, we successfully reconstruct both the lens potential and the extended source-intensity distribution of B1608+656. The resulting reconstruction can be used as the basis of a measurement of the Hubble constant. As an illustration of the astrophysical applications of our method, we use our reconstruction of the gravitational potential to study the relative distribution of mass and light in the lensing galaxies. We find that the mass-to-light ratio for the primary lens galaxy is (2.0 ± 0.2)h M☉LB,☉^-1 within the Einstein radius (3.9 h^–1 kpc), in agreement with what is found for noninteracting lens galaxies at the same scales.

Additional Information

© 2009. The American Astronomical Society. Received 2008 April 16; accepted 2008 September 23; published 2009 January 9. Print publication: Issue 1 (2009 January 20). We thank M. Bradač, J. Krist, R. Massey, C. Peng, J. Rhodes, and P. Schneider for useful discussions and the anonymous referee for helpful comments that improved the presentation of the paper. We are grateful to M. Bradač and T. Schrabback for their help with the image processing. S.H.S. thanks the Kavli Institute for Theoretical Physics for the Graduate Fellowship in the fall of 2006 and for hosting the gravitational lensing workshop, during which significant progress on this work was made. S.H.S. acknowledges the support of the NSERC (Canada) through the Postgraduate Scholarship. C.D.F. and J.P.M. acknowledge support under the HST program #GO-10158. Support for program #GO-10158 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. C.D.F. and J.P.M. acknowledge the support from the European Community's Sixth Framework Marie Curie Research Training Network Programme, contract no. MRTN-CT-2004-505183 "ANGLES." L.V.E.K. is supported in part through an NWO-VIDI career grant (project number 639.042.505). T.T. acknowledges support from the NSF through CAREER award NSF-0642621, by the Sloan Foundation through a Sloan Research Fellowship, and by the Packard Foundation through a Packard Fellowship. This work was supported in part by the NSF under award AST-0444059, the Deutsche Forschuhgsgemeinschaft under the project SCHN 342/7-1 (S.H.S), the TABASGO foundation in the form of a research fellowship (P.J.M.), and by the US Department of Energy under contract number DE-AC02-76SF00515. Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program #GO-10158.

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