A study of six low redshift QSO pairs
  The dynamical properties of six SDSS quasar pairs at z < 0.8 are
investigated. The pairs have proper transverse separation < 500 kpc, and
velocity difference along the line of sight < 500 km/s. If they are bound
systems their dynamical mass can be evaluated and compared with that of host
galaxies. Evidence is found of an excess of the former mass with respect to the
latter. This suggests that these quasar pairs are hosted by galaxies with
massive dark halos or that they reside in a group/cluster of galaxies.
