  We explore the abundance, spatial distribution, and physical properties of
the OVI, OVII, and OVIII ions of oxygen in circumgalactic and intergalactic
media (the CGM, IGM, and WHIM). We use the TNG100 and TNG300 large volume
cosmological magneto-hydrodynamical simulations. Modeling the ionization states
of simulated oxygen, we find good agreement with observations of the
low-redshift OVI column density distribution function (CDDF), and present its
evolution for all three ions from z=0 to z=4. Producing mock quasar absorption
line spectral surveys, we show that the IllustrisTNG simulations are fully
consistent with constraints on the OVI content of the CGM from COS-Halos and
other low redshift observations, producing columns as high as observed. We
measure the total amount of mass and average column densities of each ion using
hundreds of thousands of simulated galaxies spanning 10^11 < Mhalo/Msun < 10^15
corresponding to 10^9 < M*/Msun < 10^12 in stellar mass. Stacked radial
profiles of OVI are computed in 3D number density and 2D projected column,
decomposing into the 1-halo and 2-halo terms. Relating halo OVI to properties
of the central galaxy, we find a correlation between the (g-r) color of a
galaxy and the total amount of OVI in its CGM. In comparison to the COS-Halos
finding, this leads to a dichotomy of columns around star-forming versus
passive galaxies at fixed stellar (or halo) mass. We demonstrate that this
correlation is a direct result of blackhole feedback associated with quenching
and represents a causal consequence of galactic-scale baryonic feedback
impacting the physical state of the circumgalactic medium.
