Cold mode gas accretion on two galaxy groups at z ∼ 2

Abstract

We present Keck Cosmic Web Imager (KCWI) integral field spectroscopy (IFS) observations of rest-frame UV emission lines Lyα⁠, CIVλλ 1548 Å, 1550Å, and HeII 1640 Å observed in the circumgalactic medium (CGM) of two z = 2 radio-loud quasar host galaxies. We detect extended emission on 80–90 kpc scale in Lyα in both systems with CIV and HeII emission also detected out to 30–50 kpc. All emission lines show kinematics with a blue and redshifted gradient pattern consistent with velocities seen in massive dark matter haloes and similar to kinematic patterns of inflowing gas seen in hydrodynamical simulations. Using the kinematics of both resolved Lyα emission and absorption, we can confirm that both kinematic structures are associated with accretion. Combining the KCWI data with molecular gas observations with Atacama Large Millimeter/submillimeter Array (ALMA) and high-spatial resolution of ionized gas with Keck OSIRIS, we find that both quasar host galaxies reside in proto-group environments at z = 2. We estimate 1–6 × 10¹⁰ M_⊙ of warm-ionized gas within 30–50 kpc from the quasar that is likely accreting on to the galaxy group. We estimate inflow rates of 60–200 M_⊙ yr⁻¹, within an order of magnitude of the outflow rates in these systems. In the 4C 09.17 system, we detect narrow gas streams associated with satellite galaxies, potentially reminiscent of ram-pressure stripping seen in local galaxy groups and clusters. We find that the quasar host galaxies reside in dynamically complex environments, with ongoing mergers, gas accretion, ISM stripping, and outflows likely playing an important role in shaping the assembly and evolution of massive galaxies at cosmic noon.