The Influence of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \…

We analyze high-redshift structure in three hydrodynamic simulations thathave identical initial conditions and cosmological parameters and differ onlyin the value of the baryon density parameter, Omega_b=0.02, 0.05, 0.125.Increasing Omega_b does not change the fraction of baryons in the diffuse(unshocked) phase of the intergalactic medium, but it increases cooling ratesand therefore transfers some baryons from the shocked intergalactic phase tothe condensed phase associated with galaxies. Predictions of Lyman-alpha forestabsorption are almost unaffected by changes of Omega_b provided that the UVbackground intensity is adjusted so that the mean opacity of the forest matchesthe observed value. The required UV background intensity scales as Omega_b^1.7,and the higher photoionization rate increases the gas temperature in lowdensity regions. Damped Lyman-alpha absorption and Lyman limit absorption bothincrease with increasing Omega_b, though the impact is stronger for dampedabsorption and is weaker at z=4 than at z=2-3. The mass of cold gas and starsin high-redshift galaxies increases faster than Omega_b but slower thanOmega_b^2, and the global star formation rate scales approximately asOmega_b^1.5. In the higher Omega_b models, the fraction of baryonic materialwithin the virial radius of dark matter halos is usually higher than theuniversal fraction, indicating that gas dynamics and cooling can lead toover-representation of baryons in virialized systems. On the whole, our resultsimply a fairly intuitive picture of the influence of Omega_b on high-redshiftstructure, and we provide scalings that can be used to estimate the impact ofOmega_b uncertainties on the predictions of hydrodynamic simulations.