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 \langle N _ { OVI } \rangle = 14.9 \pm 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 \sim 2 – 3 galaxies .
The total velocity widths of the O VI profiles are also large ( 200 \leq \Delta v _ { OVI } \leq 400 { km s } ^ { -1 } ) .
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 \mathrel { \hbox { \hbox to 0.0 pt { \hbox { \lower 4.0 pt \hbox { $ \sim$ } } } \hbox { $ < $ } } } % 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 \sim 2 –3 , only second to the Ly \alpha forest .
We conservatively show that 5 – 20 \% of the metals ever produced at z \sim 2 –3 are in form of highly ionized metals ejected in the CGM of galaxies .