The mass profile of early-type galaxies in overdense environments: the case of the double source-plane gravitational lens SL2SJ02176-0513^*

¹ Physics Department & Shanghai Key Lab for Astrophysics, Shanghai Normal University, 100 Guilin Road, Shanghai 200234, PR China e-mail: tuhong@shnu.edu.cn
² CNRS, UMR7095, Institut d'Astrophysique de Paris, 98bis Bd Arago, 75014, Paris, France
³ UPMC Univ. Paris 6, UMR7095, Institut d'Astrophysique de Paris, 98bis Bd Arago, 75014, Paris, France
⁴ Department of Physics, University of California, Santa Barbara, CA 93106, USA
⁵ Laboratoire d'Astrophysique de Toulouse-Tarbes, Université de Toulouse, CNRS, 57 avenue d'Azereix, 65000 Tarbes, France
⁶ OAMP, Laboratoire d'Astrophysique de Marseille - UMR 6110, Traverse du siphon, 13012 Marseille, France
⁷ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
⁸ Laboratoire d'Astrophysique de Toulouse-Tarbes, CNRS-UMR 5572, and Univ. Paul Sabatier, 31400 Toulouse, France
⁹ European Southern Observatory, Alonso de Cordoba, Santiago, Chile
¹⁰ Department of Astronomy, California Institute of Technology, 105-24, Pasadena, CA91125, USA

Received: 27 February 2009
Accepted: 13 April 2009

Abstract

Context. The Strong Lensing Legacy Survey (SL2S) provides a sample of the strong lensing events associated with massive distant galaxies, some of which lie in the outskirts of galaxy groups and clusters.

Aims. We investigate the internal structure of early-type galaxies in overdense environments, where tidal forces are expected to alter dark matter haloes of infalling galaxies.

Methods. SL2SJ02176-0513 is a remarkable lens for the presence of two multiply-imaged systems at different redshifts lensed by a foreground massive galaxy at z_lens = 0.656: a bright cusp arc at z_arc = 1.847 and an additional double-image system at an estimated redshift of z_dbl ~ 2.9 based on photometry and lensing geometry. The system is located about 400 kpc away from the centre of a massive group of galaxies. Mass estimates for the group are available from X-ray observations and satellite kinematics. Multicolour photometry provides an estimate of the stellar mass of the main lens galaxy. The lensing galaxy is modelled with two components (stars and dark matter), and we include the perturbing effect of the group environment and all available constraints.

Results. We find that classic lensing degeneracies, e.g. between external convergence and mass density slope, are significantly reduced with respect to standard systems and infer tight constraints on the mass density profile: (i) the dark matter content of the main lens galaxy is in line with that of typical galaxies ; (ii) the required mass associated with the dark matter halo of the nearby group is consistent with X-ray ; (iii) accounting for the group contribution in the form of an external convergence, the slope of the mass density profile of the main lens galaxy alone is found to be , consistent with the isothermal (α = -1) slope.

Conclusions. We demonstrate that multiple source plane systems together with good ancillary dataset can be used to disentangle local and environmental effects.