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The velocity field of baryonic gas in the universe | | Bryan Kim
; Ping He
; Jesús Pando
; Long-Long Feng
; Li-Zhi Fang
; | | Date: |
9 Feb 2005 | | Journal: | Astrophys.J. 625 (2005) 599-612 | | Subject: | astro-ph | | Affiliation: | 2 and 3), Jesús Pando , Long-Long Feng (2 and 4), Li-Zhi Fang ( DePaul University, National Astronomical Observatories --China, Univeristy of Arizona, Purple Mountain Observatory | | 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., $P(Delta v)=(1 r^y)F(Delta v/r^y)$. 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. | | Source: | arXiv, astro-ph/0502175 | | Services: | Forum | Review | PDF | Favorites | |
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