Galactic and Circumgalactic OVI and its Impact on the Cosmological Metal
  and Baryon Budgets at 2<z<3.5
  We present the first results from our NASA Keck Observatory Database of
Ionized Absorbers toward Quasars (KODIAQ) survey which aims to characterize the
properties of the highly ionized gas of high redshift galaxies and their
circumgalactic medium (CGM) at 2<z<4. We select absorbers optically thick at
the Lyman limit ({\tau}LL > 1, log N(HI) > 17.3) as probes of these galaxies
and their CGM where both transitions of the O VI doublet have little
contamination from the Ly {\alpha}, {\beta} forests. We found 20 absorbers that
satisfy these rules: 7 Lyman limit systems (LLSs), 8 super-LLSs (SLLSs) and 5
damped Ly{\alpha} (DLAs). The O VI detection rate is 100% for the DLAs, 71% for
the LLSs, and 63% for the SLLSs. When O VI is detected, log N(OVI)=14.9+/-0.3,
an average O VI column density substantially larger and with a smaller
dispersion than found in blind O VI surveys at similar redshifts. Strong O VI
absorption is therefore nearly ubiquitous in the CGM of z~2-3 galaxies. The
total velocity widths of the O VI profiles are also large (200<Dv(OVI)<400
km/s). These properties are quite similar to those seen for O VI in low z
star-forming galaxies, and therefore we hypothesize that these strong CGM O VI
absorbers (with {\tau}LL > 1) at 2<z<3.5 also probe outflows of star-forming
galaxies. The LLSs and SLLSs with no O VI absorption have properties consistent
with those seen in cosmological simulations tracing cold streams feeding
galaxies. When the highly ionized (Si IV and O VI) gas is taken into account,
we determine that the {\tau}LL > 1 absorbers could contain as much as 3-14% of
the cosmic baryon budget at z~2-3, only second to the Ly{\alpha} forest. We
conservatively show that 5-20% of the metals ever produced at z~2-3 are in form
of highly ionized metals ejected in the CGM of galaxies.
