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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, abackground quasar can be used to study a foreground quasar's halo gas inabsorption, providing a wealth of information about feedback, quenching, andthe physics of massive galaxy formation. We present a Keck/HIRES spectrum ofthe 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. Ourechelle spectrum reveals optically thick gas (NHI~10^19.7), coincident with theforeground quasar redshift. The ionic transitions of associated metal-linesreveal the following properties of the foreground quasar's halo: (1) thekinematics are extreme with absorption extending to +780km/s relative to z_fg;(2) the metallicity is nearly solar; (3) the temperature of the predominantlyionized gas is T<~20,000K; (4) the electron density is n_e~1 cm^-3 indicating acharacteristic size ~10 - 100pc for the absorbing `clouds'; (7) there is anegligible amount of warm gas 10^5K < T < 10^6K; (8) the gas is unlikelyilluminated by the foreground quasar, implying anisotropic or intermittentemission. The mass of cold T~10^4K gas implied by our observations issignificant, amounting to a few percent of the total expected baryonic massdensity of the foreground quasar's dark halo at r~100kpc. The origin of thismaterial is still unclear, and we discuss several possibilities in the contextof current models of feedback and massive galaxy formation.

Quasars Probing Quasars III: New Clues to Feedback, Quenching, and the Physics of Massive Galaxy Formation