2024ApJ...964...84S

We present results from the Quasar hosts Unveiled by high Angular Resolution Techniques survey studying the circumgalactic medium (CGM) by observing rest-frame UV emission lines Lyα, C IV, and He II around two radio-loud quasars, 3C 9 (z = 2.02) and 4C 05.84 (z = 2.32), using the Keck Cosmic Web Imager. We detect large-scale Lyα nebulae around both quasars with projected diameters ∼100 kpc, with spatially resolved, embedded 15-30 kpc He II and C IV nebulae around both quasars as well as kinematically distinct He II and C IV nebulae at a physical separation of ∼15 kpc from both quasars. Observations of Hα, Hβ, and [O III] emission using Keck MOSFIRE spectroscopically confirm that the Lyα nebulae extend to companion galaxies and that these quasars are in a protogroup/protocluster environment. We confirm that the He II and C IV emission is kinematically and spatially coincident with the companion galaxies. We estimate the virial masses of the companion galaxies, their metallicities, and star formation rates, and investigate the sources of ionization. We measure the dynamical mass of the host dark matter halos and estimate that the dark matter halos of these systems will grow to a mass of 2 × 10¹⁴M_⊙ (3C 9) and 2 × 10¹³M_⊙ (4C 05.84) by z = 0. The combined CGM and companion galaxies observations indicate Lyα substructure can indicate the presence of companion galaxies in the CGM.