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(gzipped) PostScript## Lagrangian theory of structure formation in pressure-supported cosmological fluids
The Lagrangian theory of structure formation in cosmological fluids, restricted to the matter model "dust", provides successful models of large-scale structure in the Universe in the laminar regime, i.e., where the fluid flow is single-streamed and "dust"-shells are smooth. Beyond the epoch of shell-crossing a qualitatively different behavior is expected, since in general anisotropic stresses powered by multi-stream forces arise in collisionless matter. In this paper we provide the basic framework for the modeling of pressure-supported fluids, restricting attention to isotropic stresses and to the cases where pressure can be given as a function of the density. We derive the governing set of Lagrangian evolution equations and study the resulting system using Lagrangian perturbation theory. We discuss the first-order equations and compare them to the Eulerian theory of gravitational instability, as well as to the case of plane-symmetric collapse. We obtain a construction rule that allows to derive first-order solutions of the Lagrangian theory from known first-order solutions of the Eulerian theory and so extend Zel'dovich's extrapolation idea into the multi-streamed regime. These solutions can be used to generalize current structure formation models in the spirit of the "adhesion approximation".
Online publication: March 1, 1999 |