On the OVI Abundance in the Circumgalactic Medium of Low-Redshift
  Galaxies
  We analyze the mass, temperature, metal enrichment, and OVI abundance of the
circumgalactic medium (CGM) around $z\sim 0.2$ galaxies of mass $10^9 M_\odot
<M_\bigstar < 10^{11.5} M_\odot$ in the Illustris simulation. Among
star-forming galaxies, the mass, temperature, and metallicity of the CGM
increase with stellar mass, driving an increase in the OVI column density
profile of $\sim 0.5$ dex with each $0.5$ dex increase in stellar mass.
Observed OVI column density profiles exhibit a weaker mass dependence than
predicted: the simulated OVI abundance profiles are consistent with those
observed for star-forming galaxies of mass $M_\bigstar = 10^{10.5-11.5}
M_\odot$, but underpredict the observed OVI abundances by $\gtrsim 0.8$ dex for
lower-mass galaxies. We suggest that this discrepancy may be alleviated with
additional heating of the abundant cool gas in low-mass halos, or with
increased numerical resolution capturing turbulent/conductive mixing layers
between CGM phases. Quenched galaxies of mass $M_\bigstar = 10^{10.5-11.5}
M_\odot$ are found to have 0.3-0.8 dex lower OVI column density profiles than
star-forming galaxies of the same mass, in qualitative agreement with the
observed OVI abundance bimodality. This offset is driven by AGN feedback, which
quenches galaxies by heating the CGM and ejecting significant amounts of gas
from the halo. Finally, we find that the inclusion of the central galaxy's
radiation field may enhance the photoionization of the CGM within $\sim 50$
kpc, further increasing the predicted OVI abundance around star-forming
galaxies.
