EDP Sciences
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Volume 386, Number 1, April IV 2002
Page(s) 69 - 76
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20020056

A&A 386, 69-76 (2002)
DOI: 10.1051/0004-6361:20020056

The lensing system towards the doubly imaged quasar SBS 1520+530

C. Faure1, 2, F. Courbin3, 4, J. P. Kneib2, D. Alloin1, M. Bolzonella2, 5 and I. Burud6, 4

1  European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago 19, Chile
2  Observatoire Midi-Pyrénées, UMR 5572, 14 avenue Édouard Belin, 31400 Toulouse, France
3  Universitad Católica de Chile, Departamento de Astronomia y Astrofisica, Casilla 306, Santiago 22, Chile
4  Institut d'Astrophysique et de Géophyique de Liège, avenue de Cointe 5, 4000 Liège, Belgium
5  Istituto di Fisica Cosmica "G. Occhialini", Milano, Italy
6  Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA

(Received 13 November 2001 / Accepted 8 January 2002 )

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+0.10-0.25. 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.

Key words: galaxies: clusters: general -- gravitational lensing -- quasar: general -- quasars: individual: SBS 1520+530

Offprint request: C. Faure, cfaure@eso.org

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© ESO 2002

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