Spatial distribution of O VI covering fractions in the simulated circumgalactic medium

We use adaptive mesh refinement cosmological simulations to study the spatial distribution and covering fraction of O VI absorption in the circumgalactic medium (CGM) as a function of projected virial radius and azimuthal angle. We compare these simulations to an observed sample of 53 galaxies from the Multiphase Galaxy Halos Survey. Using MOCKSPEC, an absorption-line analysis pipeline, we generate synthetic quasar absorption-line observations of the simulated CGM. To best emulate observations, we studied the averaged properties of 15,000 “mock samples,” each of 53 sight lines having a distribution of D R_vir and sight-line orientation statistically consistent with the observations. We find that the O VI covering fraction obtained for the simulated galaxies agrees well with the observed value for the inner halo (D R_vir ≤ 0.375) and is within 1.1σ in the outer halo (D R_vir > 0.75), but is underproduced within 0.375 < D R_vir ≤ 0.75. The observed bimodal distribution of the O VI covering fraction with azimuthal angle, showing a higher frequency of absorption along the projected major and minor axes of galaxies, is not reproduced in the simulations. Further analysis reveals the spatial-kinematic distribution of O VI-absorbing gas is dominated by outflows in the inner halo mixed with an inflowing gas that originates from farther out in the halo. Though the CGM of the individual simulated galaxies exhibits spatial structure, the flat azimuthal distribution occurs because the individual simulated galaxies do not develop a CGM structure that is universal from galaxy to galaxy.