Quasars Probing Quasars III: New Clues to Feedback, Quenching, and the Physics of Massive Galaxy Formation
Abstract
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 zfg=2.4360 +/- 0.0005, precisely determined from Gemini/GNIRS near-IR spectroscopy. Our echelle spectrum reveals optically thick gas (NHI~1019.7), 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 zfg; (2) the metallicity is nearly solar; (3) the temperature of the predominantly ionized gas is T<~20,000K; (4) the electron density is ne~1 cm-3 indicating a characteristic size ~10 - 100pc for the absorbing `clouds'; (7) there is a negligible amount of warm gas 105K < T < 106K; (8) the gas is unlikely illuminated by the foreground quasar, implying anisotropic or intermittent emission. The mass of cold T~104K 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.