Low-metallicity gas clouds in a galaxy protocluster at redshift 2.38

We present high-resolution spectroscopy of a QSO whose sight line passes through the halo of a pair of elliptical galaxies at redshift 2.38. This pair of galaxies probably lies at the center of a galaxy protocluster and is embedded in a luminous extended Lyα nebula. The QSO sight line intersects two small gas clouds within this halo. These clouds have properties similar to those of high-velocity clouds seen in the halo of the Milky Way. The gas is in a cool (<2 × 10⁴ K) and at least 20% neutral phase, with metallicities in the range -3.0 < [Fe/H] < -1.1 and neutral hydrogen column densities of ∼10^19.5 cm^-2. The origin of these clouds is unclear. The presence of low-metallicity gas within this possible protocluster implies either that the intracluster medium has not been enriched with metals at this redshift, or the clouds are embedded within a hot, ionized, metal-rich gas phase.