2019ApJ...885...61R

We present results from the Keck Baryonic Structure Survey (KBSS) including the first detailed measurements of the column densities, kinematics, and internal energy of metal-bearing gas within the virial radius (35-100 physical kpc) of eight ∼L* galaxies at z ∼ 2. From our full sample of 130 metal-bearing absorbers, we infer that halo gas is kinematically complex when viewed in singly, doubly, and triply ionized species. Broad O VI and C IV absorbers are detected at velocities similar to the lower-ionization gas but with a very different kinematic structure, indicating that the circumgalactic medium (CGM) is multiphase. There is a high covering fraction of metal-bearing gas within 100 kpc, including highly ionized gas such as O VI; however, observations of a single galaxy probed by a lensed background QSO suggest the size of metal-bearing clouds is small (<400 pc for all but the O VI-bearing gas). The mass in metals found within the halo is substantial, equivalent to >=25% of the metal mass within the interstellar medium. The gas kinematics unambiguously show that 70% of galaxies with detected metal absorption have some unbound metal-enriched gas, suggesting galactic winds may commonly eject gas from halos at z ∼ 2. When modeled assuming that ions with different ionization potentials can originate within a single gaseous structure, significant thermal broadening is detected in CGM absorbers that dominates the internal energy of the gas. Some 40% of the detected gas has temperatures in the range 10^4.5–5.5 K where cooling times are short, suggesting the CGM is dynamic, with constant heating or cooling to produce this short-lived thermal phase.