Where are the baryons? II. Feedback effects

Numerical simulations of the intergalactic medium have shown that at the present epoch, a significant fraction (40%-50%) of the baryonic component should be found in the (T similar to 10(6) K) warm-hot intergalactic medium (WHIM)- with several recent observational lines of evidence indicating the validity of the prediction. We here recompute the evolution of the WHIM with the following major improvements: (1) galactic superwind feedback processes from galaxy and star formation are explicitly included; (2) major metal species (O V to O IX) are computed explicitly in a nonequilibrium way; and ( 3) mass and spatial dynamic ranges are larger by factors of 8 and 2, respectively, than in our previous simulations. Here are the major findings: ( 1) Galactic superwinds have dramatic effects, increasing the WHIM mass fraction by about 20%, primarily through heating of warm gas near galaxies with density 10(1.5)Y10(4) times the mean density. ( 2) The fraction of baryons in the WHIM is increased modestly from the earlier work but is still similar to 40%-50%. (3) The gas density of the WHIM is broadly peaked at a density 10-20 times the mean density, ranging from underdense regions to regions that are overdense by 10(3)-10(4). ( 4) The median metallicity of the WHIM is 0.18 Z(circle dot) for oxygen, with 50% and 90% intervals being (0.040, 0.38) and (0.0017, 0.83).