Journal Article

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

Weishan Zhu, Long-Long Feng and Li-Zhi Fang

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 415, issue 2, pages 1093-1104
Published in print August 2011 | ISSN: 0035-8711
Published online July 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.18640.x
Dynamical effect of the turbulence of the intergalactic medium on the baryon fraction distribution

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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 fb will deviate from its cosmic mean fcosmicb. 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 fb 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 1011 h−1 M. The baryon fraction in haloes with mass equal to or smaller than 1011 h−1 M should be substantially lower than fcosmicb. Numerical results show that fb is decreasing from 0.8fcosmicb at halo mass scales around 1012 h−1 M to 0.3fcosmicb at 1011 h−1 M and shows further decrease when halo mass is less than 1011 h−1 M. The strong mass dependence of fb is similar to the observed results. Although the simulated fb 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 ≤1012 h−1 M.

Keywords: methods: numerical; intergalactic medium; cosmology: theory; large-scale structure of Universe

Journal Article.  8761 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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