Dynamical analysis of strong-lensing galaxy groups at intermediate
  redshift
  We present VLT spectroscopic observations of 7 discovered galaxy groups
between 0.3<z<0.7. The groups were selected from the Strong Lensing Legacy
Survey (SL2S), a survey that consists in 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. Their virial masses are between 10^13 and 10^14 M_sun, and so 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
sub-structures. We find a good agreement between the velocity dispersions
estimated from the analysis of the kinematics of group galaxies and the weak
lensing measurements, and conclude that the dynamics of baryonic matter is a
good tracer of the total mass content in galaxy groups.
