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Hubble Constant from the Gravitational Lens B1608+656

Koopmans, L. V. E. and Treu, T. and Fassnacht, C. D. and Blandford, R. D. and Surpi, G. (2003) Hubble Constant from the Gravitational Lens B1608+656. Astrophysical Journal, 599 (1). pp. 70-85. ISSN 0004-637X. doi:10.1086/379226.

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We present a refined gravitational lens model of the four-image lens system B1608+656 based on new and improved observational constraints: (1) the three independent time delays and flux ratios from Very Large Array observations, (2) the radio-image positions from Very Large Baseline Array observations, (3) the shape of the deconvolved Einstein ring from optical and infrared Hubble Space Telescope images, (4) the extinction-corrected lens-galaxy centroids and structural parameters, and (5) a stellar velocity dispersion, σ_(ap) = 247 ± 35 km s^(-1), of the primary lens galaxy (G1), obtained from an echelle spectrum taken with the Keck II Telescope. The lens-mass model consists of two elliptical mass distributions with power-law density profiles and an external shear, totaling 22 free parameters, including the density slopes that are the key parameters for determining the value of H_0 from lens time delays. This has required the development of a new lens code that is highly optimized for speed. The minimum-χ^2 model reproduces all observations very well, including the stellar velocity dispersion and the shape of the Einstein ring. A combined gravitational lens and stellar dynamical analysis leads to a value of the Hubble constant of H_0 = 75^(+7)_(-6) km s^(-1) Mpc^(-1) (68% CL; Ω_m = 0.3, Ω_Λ = 0.7). The nonlinear error analysis includes correlations between all free parameters, in particular the density slopes of G1 and G2, yielding an accurate determination of the random error on H_0. The lens galaxy G1 is ~5 times more massive than the secondary lens galaxy (G2) and has a mass density slope of γ‘_(G1)= 2.03^(+0.14)_(-0.14) ± 0.03 (68% CL) for ρ ∝ r^(-γ’), very close to isothermal (γ' = 2). After extinction correction, G1 exhibits a smooth surface brightness distribution with an R^(1/4) profile and no apparent evidence for tidal disruption by interactions with G2. Given the scope of the observational constraints and the gravitational lens models, as well as the careful corrections to the data, we believe this value of H_0 to be little affected by known systematic errors (≾5%).

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Koopmans, L. V. E.0000-0003-1840-0312
Treu, T.0000-0002-8460-0390
Fassnacht, C. D.0000-0002-4030-5461
Blandford, R. D.0000-0002-1854-5506
Additional Information:© 2003 The American Astronomical Society. Received 2003 June 10; accepted 2003 August 19. Based on observations collected at W. M. Keck Observatory, which is operated jointly by the California Institute of Technology and the University of California, and with the NASA/ESA Hubble Space Telescope, obtained at STScI, which is operated by AURA, under NASA contract NAS5-26555. We thank Richard Ellis and Jean-Paul Kneib for useful comments on this manuscript and stimulating conversations. We are grateful to an anonymous referee for comments that helped clarify the manuscript. The use of the Gauss-Hermite pixel fitting software developed by R. P. van der Marel is gratefully acknowledged. The ESI data were reduced using software developed in collaboration with D. Sand. We acknowledge the use of the HST data collected by the CASTLES collaboration. L. V. E. K. and T. T. acknowledge support by NASA through grant AR-09960 from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, under NASA contract NAS5-26555. L. V. E. K. also acknowledges an STScI Fellowship grant. T. T. acknowledges support from NASA through Hubble Fellowship grant HST-HF-01167.01-A. L. V. E. K. and R. D. B. acknowledge NSF grants AST 99-00866 and 0206286, and G. S. acknowledges NASA grant NAG5-7007 and CONICET in Argentina. We thank J. Miller, M. Bolte, R. Guhathakurta, D. Zaritsky, and all the people who worked to make ESI such a nice instrument. Finally, the authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
Funding AgencyGrant Number
Space Telescope Science InstituteUNSPECIFIED
NASA Hubble FellowshipHST-HF-01167.01-A
NSFAST 99-00866
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)UNSPECIFIED
Subject Keywords:distance scale — galaxies: elliptical and lenticular, cD — galaxies: kinematics and dynamics — galaxies: structure — gravitational lensing
Issue or Number:1
Record Number:CaltechAUTHORS:20190604-102329354
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Official Citation:L. V. E. Koopmans et al 2003 ApJ 599 70
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:96106
Deposited By: Tony Diaz
Deposited On:04 Jun 2019 18:00
Last Modified:16 Nov 2021 17:18

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