  Galaxies hosting z~2 quasars are the high-$z$ progenitors of today's massive
`red-and-dead' galaxies. With close pairs of quasars at different redshifts, a
background quasar can be used to study a foreground quasar's halo gas in
absorption, providing a wealth of information about feedback, quenching, and
the physics of massive galaxy formation. We present a Keck/HIRES spectrum of
the bright background quasar in a projected pair with angular separation 13.3"
corresponding to 108kpc at the redshift of the foreground quasar z_fg=2.4360
+/- 0.0005, precisely determined from Gemini/GNIRS near-IR spectroscopy. Our
echelle spectrum reveals optically thick gas (NHI~10^19.7), coincident with the
foreground quasar redshift. The ionic transitions of associated metal-lines
reveal the following properties of the foreground quasar's halo: (1) the
kinematics are extreme with absorption extending to +780km/s relative to z_fg;
(2) the metallicity is nearly solar; (3) the temperature of the predominantly
ionized gas is T<~20,000K; (4) the electron density is n_e~1 cm^-3 indicating a
characteristic size ~10 - 100pc for the absorbing `clouds'; (7) there is a
negligible amount of warm gas 10^5K < T < 10^6K; (8) the gas is unlikely
illuminated by the foreground quasar, implying anisotropic or intermittent
emission. The mass of cold T~10^4K gas implied by our observations is
significant, amounting to a few percent of the total expected baryonic mass
density of the foreground quasar's dark halo at r~100kpc. The origin of this
material is still unclear, and we discuss several possibilities in the context
of current models of feedback and massive galaxy formation.
