KODIAQ-Z: Metals and Baryons in the Cool Intergalactic and Circumgalactic Gas at 2.2<z<3.6
We present the KODIAQ-Z survey aimed to characterize the cool, photoionized gas at 2.2 100) between absorbers separated by less than 500 km/s imply that the metals are poorly mixed in 14.6<log N(HI)<20 gas. We show that these photoionized absorbers contribute to about 10% of the cosmic baryons and 30% of the cosmic metals at 2.2<z<3.6. We find the mean metallicity increases with N(HI), consistent with what is found in z<1 gas. The metallicity of gas in this column density regime has increased by a factor ~8 from 2.2<z<3.6 to z<1, but the contribution of the 14.6<log N(HI)<19 absorbers to the total metal budget of the universe at z<1 is half that at 2.2<z<3.6, indicating a substantial shift in the reservoirs of metals between these two epochs. We compare the KODIAQ-Z results to FOGGIE cosmological zoom simulations. The simulations show an evolution of [X/H] with N(HI) similar to our observational results. Very metal-poor absorbers with [X/H]<-2.4 at z~2-3 in these simulations are excellent tracers of inflows, while higher metallicity absorbers are a mixture of inflows and outflows.