1999/11/30 by A. Taruya, Atsushi Taruya, Jiro Soda +1 · 8 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics #Classical mechanics #Cold dark matter #Cosmology #Cosmology and Gravitation Theories #Dark energy #Dark matter #Galaxies: Formation, Evolution, Phenomena #Galaxy #Matter power spectrum #Physics #Quantum mechanics #Spectral density #Spectral index #Spectral line #Spherical model #Statistical physics #astro-ph #gr-qc
paper · pdf · doi:10.1046/j.1365-8711.2000.03615.x
published in Monthly Notices of the Royal Astronomical Society 317(4), 873-879 (Oxford University Press) · 7 pages, 3 figures, MNRAS (2000) in press
arxiv created 2000/04/20 · openalex publication_date 2000/10/01 · arxiv updated 2009/11/30 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We discuss the influence of the cosmological background density field on the spherical infall model. The spherical infall model has been used in the Press-Schechter formalism to evaluate the number abundance of clusters of galaxies, as well as to determine the density parameter of the Universe from the infalling flow. Therefore, the understanding of collapse dynamics plays a key role for extracting cosmological information. Here, we consider a modified version of the spherical infall model. We derive the mean field equations from the Newtonian fluid equations, in which the influence of cosmological background inhomogeneity is incorporated into the averaged quantities as the backreaction. By calculating the averaged quantities explicitly, we obtain simple expressions and find that, in the case of a scale-free power spectrum, density fluctuations with a negative spectral index make the infalling velocities slow. This suggests that we underestimate the density parameter Ω when using the simple spherical infall model. In cases with the index n>0, the effect of background inhomogeneity could be negligible and the spherical infall model becomes a good approximation for infalling flows. We also present a realistic example with a cold dark matter power spectrum. In this case, the mean infall tends to be slow owing to the anisotropic random velocity.