High-ionisation oxygen absorption from the Warm-Hot Intergalactic Medium
  in Simba
  We examine the physical conditions, environments, and statistical properties
of intergalactic Ovi, Ovii and Oviii absorbers in the Simba cosmological
hydrodynamic simulation suite. The goal is to understand the nature of these
high ionisation absorbers, and test Simba's surprising prediction that $\sim
70\%$ of cosmic baryons at $z=0$ are in the Warm-Hot Intergalactic Medium
(WHIM) driven by jet feedback from active galactic nuclei (AGN). By comparing a
full-physics Simba run versus one with jets turned off, we find that jet
feedback causes widespread heating that impacts the absorption morphology
particularly of the higher ions. However, the distribution of the physical
properties of detectable absorbers are not dramatically affected. Higher
ionisation absorbers probe hotter gas as expected, but in Simba all ions arise
at similar overdensities (typically $\delta\sim20-30$), similar environments
(predominantly filaments), and similar nearest-halo distances (typically
$\sim2-3r_{200c}$). Simba matches the observed Ovi column density distribution
function (CDDF) fairly well, but under-predicts the CDDF preliminarily derived
from two detected intergalactic Ovii absorbers. Predicted CDDFs are very
similar at $z=1$ with or without jets, but show differences by $z=0$
particularly at the high-column end. Despite some discrepancies, Simba
reproduces available observations as well as or better than other comparable
simulations, suggesting that Simba's widespread jet heating cannot be ruled out
by these data. These results offer hope that future X-ray and ultraviolet
facilities could provide significant constraints on galactic feedback models
from high-ionisation IGM metal absorbers.
