Circum-galactic medium in the halo of quasars
  The properties of circum-galactic gas in the halo of quasar host galaxies are
investigated analyzing Mg II 2800 and C IV 1540 absorption-line systems along
the line of sight close to quasars. We used optical spectroscopy of closely
aligned pairs of quasars (projected distance $\leq$ 200 kpc, but at very
different redshift) obtained at the VLT and Gran Telescopio Canarias to
investigate the distribution of the absorbing gas for a sample of quasars at
z$\sim$1. Absorption systems of EW $\geq$ 0.3 $\rm{\AA}$ associated with the
foreground quasars are revealed up to 200 kpc from the centre of the host
galaxy, showing that the structure of the absorbing gas is patchy with a
covering fraction quickly decreasing beyond 100 kpc. In this contribution we
use optical and near-IR images obtained at VLT to investigate the relations
between the properties of the circum-galactic medium of the host galaxies and
of the large scale galaxy environments of the foreground quasars.
