QUASARS PROBING QUASARS. III. NEW CLUES TO FEEDBACK, QUENCHING, AND THE PHYSICS OF MASSIVE GALAXY FORMATION

Galaxies hosting z similar to 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/High Resolution Echelle Spectrometer spectrum of the bright background quasar in a projected pair with angular separation theta = 13.3 arcsec corresponding to R-perpendicular to = 108 kpc at the redshift of the foreground quasar z(fg) = 2.4360 +/- 0.0005, precisely determined from Gemini/Gemini Near-Infrared Spectrograph near-IR spectroscopy. Our echelle spectrum reveals optically thick gas (N-HI approximate to 10(19.7) cm(-2)) 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 +780 km s(-1) relative to z(fg); (2) the metallicity is nearly solar; (3) the temperature of the predominantly ionized gas is T <= 20,000 K; (4) the electron density is n(e) similar to 1 cm(-3) indicating a characteristic size similar to 10-100 pc for the absorbing clouds; (5) there is little (if any) warm gas 10(5) K less than or similar to T less than or similar to 10(6) K; (6) the gas is unlikely illuminated by the foreground quasar, implying anisotropic or intermittent emission. The mass of cold T similar to 10(4) K 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 similar to 100 kpc. 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.