Using the state-of-the-art cosmological hydrodynamic simulations of the standard cold dark matter model with star formation feedback strength normalized to match the observed star formation history of the universe at z = 0 - 6 , we compute the metal enrichment history of the intergalactic medium ( IGM ) .
Overall we show that galactic superwind ( GSW ) feedback from star formation can transport metals to the IGM and that the properties of simulated metal absorbers match current observations .
The distance of influence of GSW from galaxies is typically limited to about \leq 0.5 Mpc and within regions of overdensity \delta \geq 10 .
Most C IV and O VI absorbers are located within shocked regions of elevated temperature ( T \geq 2 \times 10 ^ { 4 } K ) , overdensity ( \delta \geq 10 ) , and metallicity ( [ Z / { Z _ { \odot } } ] = [ -2.5 , -0.5 ] ) , enclosed by double shocks propagating outward .
O VI absorbers have typically higher metallicity , lower density and higher temperature than C IV absorbers .
For O VI absorbers collisional ionization dominates over the entire redshift range z = 0 - 6 , whereas for C IV absorbers the transition occurs at moderate redshift z \sim 3 from collisionally dominated to photoionization dominated .
We find that the observed column density distributions for C IV and O VI in the range \log N { cm } ^ { 2 } = 12 - 15 are reasonably reproduced by the simulations .
The evolution of mass densities contained in C IV and O VI lines , \Omega _ { CIV } and \Omega _ { OVI } , is also in good agreement with observations , which shows a near constancy at low redshifts and an exponential drop beyond redshift z = 3 - 4 .
For both C IV and O VI most absorbers are transient and the amount of metals probed by C IV and O VI lines of column \log N { cm } ^ { 2 } = 12 - 15 is only \sim 2 \% of total metal density at any epoch .
While gravitational shocks from large-scale structure formation dominate the energy budget ( 80 - 90 \% ) for turning about 50 % of IGM to the warm-hot intergalactic medium ( WHIM ) by z = 0 , GSW feedback shocks are energetically dominant over gravitational shocks at z \geq 1 - 2 .
Most of the so-called “ missing metals ” at z = 2 - 3 are hidden in a warm-hot ( T = 10 ^ { 4.5 - 7 } K ) gaseous phase , heated up by GSW feedback shocks .
Their mass distribution is broadly peaked at \delta = 1 - 10 in the IGM , outside virialized halos .
Approximately ( 37 , 46 , 10 , 7 ) \% of the total metals at z = 0 are in ( stars , WHIM , X-ray gas , cold gas ) ; the distribution stands at ( 23 , 57 , 2 , 18 ) \% and ( 14 , 51 , 4 , 31 ) \% at z = 2 and z = 4 , respectively .