2025ApJ...993...44G

This paper investigates the physical conditions of the circumgalactic medium of L^⋆ galaxies through explorations of observed ion tracer gas kinematics and comparisons of observations to different ionization models. For this analysis, we utilize C IV observations from the CIViL^⋆ survey (∼0.14 ≤ z_gal ≤ 0.25) and directly compare them to observations of matched lines of sight from the Cosmic Origins Spectrograph-Halos survey. We find that the kinematic parameters for C IV and O VI are likely (>95%) drawn from the same parent distribution, suggesting that these two ions are kinematically coincident and potentially originate under the same physical conditions. We find that the measured C IV/O VI and N V/O VI ratios are inconsistent with single-phase equilibrium models. For 70% of the objects in our sample, regions allowed by the column density ratios in the density-temperature space do not overlap, creating a “zone of avoidance.” We also investigate the origins of C IV, N V, and O VI by exploring a cooling flow model under collisional ionization. We find that both N V and O VI are consistent with the predictions of the model, but the column densities of C IV are ∼2.5 times higher than the predictions. As C IV has a lower ionization energy than N V and O VI, it is possible that C IV has contributions from both the warm/hot and cool photoionized phase.