Previrialization: Perturbative and NBody Results
Abstract
We present a series of Nbody experiments which confirm the reality of the previrialization effect. We use also a weakly nonlinear perturbative approach to study the phenomenon. These two approaches agree when the rms density contrast, σ, is small; more surprisingly, they remain in agreement when σ ~ 1. When the slope of the initial power spectrum is n > 1, nonlinear tidal interactions slow down the growth of density fluctuations, and the magnitude of the suppression increases when n (i.e., the relative amount of smallscale power) is increased. For n < 1, we see an opposite effect: the fluctuations grow more rapidly than in linear theory. The transition occurs at n = 1 when the weakly nonlinear correction to σ is close to zero and the growth rate is close to linear. Our results resolve recent controversy between two N body studies of previrialization. Peebles assumed n = 0 and found strong evidence in support of previrialization, while Evrard & Crone, who assumed n = 1, reached opposite conclusions. As we show here, the initial conditions with n = 1 are rather special because the nonlinear effects nearly cancel out for that particular spectrum. In addition to our calculations for scalefree initial spectra, we show results for a more realistic spectrum of Peacock & Dodds. Its slope near the scale usually adopted for normalization is close to 1, so σ is close to linear. Our results retroactively justify linear normalization at 8 h^1^ Mpc while also demonstrating the danger and limitations of this practice.
 Publication:

The Astrophysical Journal
 Pub Date:
 August 1996
 DOI:
 10.1086/177580
 arXiv:
 arXiv:astroph/9508032
 Bibcode:
 1996ApJ...467....1L
 Keywords:

 COSMOLOGY: THEORY;
 GALAXIES: FORMATION;
 COSMOLOGY: LARGESCALE STRUCTURE OF UNIVERSE;
 Astrophysics
 EPrint:
 Significantly revised, 25 pages, uuencoded compressed postscript, figures included, to appear in ApJ