Browsing by Author "Faure, C"

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    A search for clusters and groups of galaxies on the line of sight towards 8 lensed quasars
    (2004) Faure, C; Alloin, D; Kneib, JP; Courbin, F
    In this paper we present new ESO/VLT FORS1 and ISAAC images of the fields around eight gravitationally lensed quasars: CTQ 414, HE 0230-2130, LBQS 1009-0252, B 1030+074, HE 1104-1805, B 1359+154, H 1413+117 and HE 2149-2745. When available and deep enough, HST/WFPC2 data were also used to infer the photometric redshifts of the galaxies around the quasars. The search of galaxy overdensities in space and redshift, as well as a weak-shear analysis and a mass reconstruction are presented in this paper. We find that there are most probably galaxy groups towards CTQ 414, HE 0230-2130, B 1359+154, H 1413+117 and HE 2149-2745, with masses <4x10(14) M-circle dot h(-1). Considering its photometric redshift, the galaxy group discovered in the field around HE 1104-1805 is associated with the quasar rather than with the lensing potential.
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    The lensing system towards the doubly imaged quasar SBS 1520+530
    (2002) Faure, C; Courbin, F; Kneib, JP; Alloin, D; Bolzonella, M; Burud, I
    The gravitational potential responsible for the lensing effect in SBS 1520+530 is studied over length scales from a few arc-seconds to a few arc-minutes. For this purpose, we use sharply deconvolved Hubble Space Telescope images in the optical and near-IR, in combination with ground based optical data obtained over a wider field-of-view. In particular, we have carried out a multi-color analysis in order to identify groups or clusters of galaxies along the line of sight. Photometric redshifts are measured for 139 galaxies unveiling significant excesses of galaxies 1.0' NW and 1.7' SW of the main lensing galaxy. The photometric redshift inferred both for the main lensing galaxy and for the galaxy concentrations is z = 0.9(-0.25)(+0.10). This is in rough agreement with the measured spectroscopic redshift of the main lensing galaxy, z = 0.71 (Burud et al. 2002), suggesting that it is part of a larger group or cluster. We investigate the impact of including the galaxy cluster, first on the modelling of the lensing system, and second on the expected time-delay between the two quasar images.
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    Time delay and lens redshift for the doubly imaged BAL quasar SBS 1520+530
    (2002) Burud, I; Hjorth, J; Courbin, F; Cohen, JG; Magain, P; Jaunsen, AO; Kaas, AA; Faure, C; Letawe, G
    We present optical R-band light curves of the gravitationally lensed quasar SBS 1520+530 derived from data obtained at the Nordic Optical Telescope. A time delay of 130 +/- 3 days (1sigma) is determined from the light curves. In addition, spectra of SBS 1520+530 obtained at the Keck Observatory are spatially deconvolved in order to extract the spectrum of the faint lensing galaxy, free of any contamination by the light from the bright quasar images. This spectrum indicates a lens redshift z = 0.717, in agreement with one of the absorption systems found in the quasar spectra. The best mass model of the system includes a second nearby galaxy and a cluster of galaxies in addition to the main lensing galaxy. Adopting this model and an Omega = 0.3, Lambda = 0.7 cosmology, our time-delay measurement yields a Hubble constant of H-0 = 51 +/- 9 km s(-1) Mpc(-1) (1sigma error).