Dynamical effect of the turbulence of the intergalactic medium on the baryon fraction distribution

We investigate the dynamical effect of turbulence in the baryonic intergalactic medium (IGM) on the baryon fraction distribution. In the fully developed non-linear regime, the IGM will evolve into a state of turbulence, containing strong and curved shocks, vorticity and complex structures. Turbulence would mean that the density and velocity fields of the IGM would be different from those of the underlying collisionless dark matter. Consequently, the baryon fraction f(b) will deviate from its cosmic mean f(b)(cosmic). We study these phenomena with simulation samples produced by the weighted essentially non-oscillatory (WENO) hybrid cosmological hydrodynamic/N-body code, which is effective for capturing shocks and complex structures. We find that the distribution of the baryon fraction is highly non-uniform on scales from hundreds of kpc to a few Mpc, and f(b) varies from as low as 1 per cent to a few times the cosmic mean. We further show that the turbulence pressure in the IGM is weakly scale-dependent and comparable to the gravitational energy density of haloes with mass around 10(11) h(-1) M-circle dot. The baryon fraction in haloes with mass equal to or smaller than 10(11) h(-1) M-circle dot should be substantially lower than f(b)(cosmic). Numerical results show that f(b) is decreasing from 0.8f(b)(cosmic) at halo mass scales around 10(12) h(-1) M-circle dot to 0.3f(b)(cosmic) at 10(11) h(-1) M-circle dot and shows further decrease when halo mass is less than 10(11) h(-1) M-circle dot. The strong mass dependence of f(b) is similar to the observed results. Although the simulated f(b) in haloes are higher than the observed value by a factor of 2, the turbulence of the IGM should be an important dynamical reason for the remarkable lack of baryonic matter in haloes with mass <= 10(12) h M-1(circle dot).