The velocity field of baryonic gas in the universe

Abstract

The dynamic evolution of the baryonic intergalactic medium (IGM) caused by the underlying dark matter gravity is governed by the Navier-Stokes equations in which many cooling and heating processes are involved. However, it has long been recognized that the growth mode dynamics of cosmic matter clustering can be sketched by a random force driven Burgers' equation if cooling and heating are ignored. Just how well the dynamics of the IGM can be described as a Burgers fluid has not been fully investigated probably because cooling and heating are essential for a detailed understanding of the IGM. Using IGM samples produced by a cosmological hydrodynamic simulation in which heating and cooling processes are properly accounted for, we show that the IGM velocity field in the nonlinear regime shows the features of a Burgers fluid, that is, when the Reynolds number is high, the velocity field consists of an ensemble of shocks. Consequently, (1) the IGM velocity $v$ is generally smaller than that of dark matter; (2) for the smoothed field, the IGM velocity shows tight correlation with dark matter given by $v\simeq s{v}_{dm}$, with $s<1$, such that the lower the redshift, the smaller $s$; (3) the velocity PDFs are asymmetric between acceleration and deceleration events; (4) the PDF of velocity difference $\Delta v=v(x+r)-v(x)$ satisfies the scaling relation for a Burgers fluid, i.e., $P(\Delta v)=(1r^y)F(\Delta v/r^y)$. We find the scaling function and parameters for the IGM which are applicable to the entire scale range of the samples (0.26 - 8 h${}^{-1}$ Mpc). These properties show that the similarity mapping between the IGM and dark matter is violated on scales much larger than the Jeans length of the IGM.

14 pages, 10 jpg-figures, accepted for publication in the Astrophysical Journal. References added

References in corpus (10)

• The Dark Matter Distribution in the Central Regions of Galaxy Clusters
• The Dark Matter Distribution in the Central Regions of Galaxy Clusters: Implications for CDM
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• Temperature and Entropy Fields of Baryonic Gas in the Universe
• Distributions of the Baryon Fraction on Large Scales in the Universe
• Intermittent Features of the QSO Ly$\alpha$ Transmitted Flux: Results from Hydrodynamic Cosmological Simulations
• Power spectrum and intermittency of the transmitted flux of QSOs Ly-alpha absorption spectra
• Hydrogen Clouds before Reionization: a Lognormal Model Approach
• The Statistical Discrepancy between the IGM and Dark Matter Fields: One-Point Statistics
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Cited by in corpus (12)

• Low-Redshift Cosmic Baryon Fluid on Large Scales and She-Leveque Universal Scaling
• Dynamical Effect of the Turbulence of IGM on the Baryon Fraction Distribution
• A Unified Fitting of HI and HeII LyαTransmitted Flux of QSO HE2347 with LCDM Hydrodynamic Simulations
• Non-Gaussianity of the Cosmic Baryon Fluid: Log-Poisson Hierarchy Model
• Log-Poisson Hierarchical Clustering of Cosmic Neutral Hydrogen and Ly-alpha Transmitted Flux of QSO Absorption Spectrum
• X-ray Emission of Baryonic Gas in the Universe: Luminosity-Temperature Relationship and Soft-Band Background
• Astrophysics in 2005
• Power Spectrum and Intermittency of Ly$\alpha$ Transmitted Flux of QSO He2347-4342
• Scaling Relation between Sunyaev-Zel'dovich Effect and X-ray Luminosity and Scale-Free Evolution of Cosmic Baryon Field
• Statistical and dynamical decoupling of the IGM from Dark Matter
• Turbulence revealed by wavelet transform: power spectrum and intermittency for the velocity field of the cosmic baryonic fluid
• A Parameter-free Statistical Measurement of Halos with Power Spectra