Volume 488, Number 2, September III 2008
|Page(s)||481 - 490|
|Section||Cosmology (including clusters of galaxies)|
|Published online||09 July 2008|
COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses *,**
VII. Time delays and the Hubble constant from WFI J2033–4723
Laboratoire d'Astrophysique, École Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, 1290 Versoix, Switzerland e-mail: email@example.com
2 Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 août 17, Sart-Tilman, Bât. B5C, 4000 Liège, Belgium
3 Department of Astronomy and the Center for Cosmology and Astroparticle Physics, The Ohio State University, Columbus, OH 43210, USA
4 Department of Physics, United States Naval Academy, 572C Holloway Road, Annapolis MD 21402, USA
5 Institute of Theoretical Physics, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland
6 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge MA 02138, USA
Accepted: 2 July 2008
Gravitationally lensed quasars can be used to map the mass distribution in lensing galaxies and to estimate the Hubble constant H0 by measuring the time delays between the quasar images. Here we report the measurement of two independent time delays in the quadruply imaged quasar WFI J2033-4723 (z = 1.66). Our data consist of R-band images obtained with the Swiss 1.2 m EULER telescope located at La Silla and with the 1.3 m SMARTS telescope located at Cerro Tololo. The light curves have 218 independent epochs spanning 3 full years of monitoring between March 2004 and May 2007, with a mean temporal sampling of one observation every 4th day. We measure the time delays using three different techniques, and we obtain = 35.5 ± 1.4 days (3.8%) and , where A is a composite of the close, merging image pair. After correcting for the time delays, we find R-band flux ratios of ± 0.04, ± 0.06, and ± 0.05 with no evidence for microlensing variability over a time scale of three years. However, these flux ratios do not agree with those measured in the quasar emission lines, suggesting that longer term microlensing is present. Our estimate of H0 agrees with the concordance value: non-parametric modeling of the lensing galaxy predicts H0 = 67 km s-1 Mpc-1, while the Single Isothermal Sphere model yields H0 = 63 km s-1 Mpc-1 (68% confidence level). More complex lens models using a composite de Vaucouleurs plus NFW galaxy mass profile show twisting of the mass isocontours in the lensing galaxy, as do the non-parametric models. As all models also require a significant external shear, this suggests that the lens is a member of the group of galaxies seen in field of view of WFI J2033-4723.
Key words: gravitational lensing / cosmology: cosmological parameters / quasars: individual: WFI J2033-4723
Based on observations obtained with the 1.2 m EULER Swiss Telescope, the 1.3 m Small and Moderate Aperture Research Telescope System (SMARTS) which is operated by the SMARTS Consortium, and the NASA/ESA Hubble Space Telescope as part of program HST-GO-9744 of the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.
© ESO, 2008
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