Dynamical analysis of strong-lensing galaxy groups at intermediate redshift ^{⋆,⋆⋆,⋆⋆⋆}

¹ Departamento de Física y Astronomía, Universidad de Valparaíso, Avda. Gran Bretaña 1111, 2360102 Valparaíso, Chile
e-mail: rmunoz@astro.puc.cl
² Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Avda. Vicuña Mackenna 4860, Casilla 306, Santiago 22, Chile
³ Centro de Investigaciones de Astronomía, AP 264, Mérida 5101–A, Venezuela
⁴ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
⁵ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Marie Vej 30, 2100 Copenhagen, Denmark
⁶ Laboratoire d’Astrophysique de Toulouse-Tarbes, Université de Toulouse, CNRS, 57 avenue d’Azereix, 65000 Tarbes, France
⁷ Institut d’Astrophysique de Paris, UMR 7095 CNRS & Université Pierre et Marie Curie, 98bis Bd Arago, 75014 Paris, France
⁸ CRAL, Université Lyon 1, Observatoire de Lyon, 9 avenue Charles André, 69561 Saint Genis Laval Cedex, France

Received: 23 November 2011
Accepted: 7 January 2013

Abstract

We present VLT spectroscopic observations of seven newly discovered galaxy groups between 0.3 < z < 0.7. The groups were selected from the Strong Lensing Legacy Survey (SL2S), a survey that consists of a systematic search for strong lensing systems in the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). We give details about the target selection, spectroscopic observations, and data reduction for the first release of confirmed SL2S groups. The dynamical analysis of the systems reveals that they are gravitationally bound structures, with at least 4 confirmed members and velocity dispersions between 300 and 800 km s^-1. Their virial masses are between 10¹³ and 10¹⁴ M_⊙, so they can be classified as groups or low mass clusters. Most of the systems are isolated groups, except two of them that show evidence of an ongoing merger of two substructures. We find that weak lensing estimates of the group velocity dispersions are 50% greater than estimates based upon the radial velocities of its members, and conclude that the dynamics of baryonic matter is a good tracer of the total mass content in galaxy groups.