Péridier Library Abstract Archive

Abstract No. UT 369

Title: Gravitational Instability in Collisionless Cosmological Pancakes
Author(s): Azita Valinia, Paul R. Shapiro, Hugo Martel, and Ethan T. Vishniac
Keywords: cosmology: theory --- dark matter --- galaxies:formation --- instabilities --- large-scale structure of universe
E-Mail: Dr. Hugo Martel (to request a full copy of this paper)
Preprint: 9610228 Document source or PostScript
Release date: 10/31/96 17:24:00
Publication status: Astrophysical Journal, in press (1997)
Comments: 61 pages, 19 figures

The gravitational instability of cosmological pancakes composed of collision- less dark matter in an Einstein-de Sitter universe is investigated numerically to demonstrate that pancakes are unstable with respect to fragmentation and the formation of filaments. A "pancake" is defined here as the nonlinear outcome of the growth of a 1D, sinusoidal, plane-wave, adiabatic density perturbation. We have used high resolution, 2D, N-body simulations by the Particle-Mesh (PM) method to study the response of pancakes to perturbation by either symmetric (density) or antisymmetric (bending or rippling) modes, with corresponding wavevectors k_s and k_a transverse to the wavevector k_p of the unperturbed pancake plane-wave. We consider dark matter which is initially "cold" (i.e., with no random thermal velocity in the initial con- ditions). We also investigate the effect of a finite, random, isotropic, initial velocity dispersion (i.e., initial thermal velocity) on the fate of pancake collapse and instability. Pancakes are shown to be gravitationally unstable with respect to all perturbations of wavelength l < l_p (where l_p = 2 pi/k_p). These results are in contradiction with the expectations of an approximate, thin-sheet energy argument.