Generation of large-scale cosmological structures by gravitational clustering

Abstract

A VARIETY of observational evidence attests to the presence of large voids, filaments and sheets in the distribution of galaxies on large cosmological scales. Similar structures have been produced by numerical simulation of the gravitational evolution of a distribution of initial density fluctuations, but there has been controversy over which initial conditions are needed to produce the desired result: the interpretation of simulations is generally hampered by their discreteness, low resolution both spatially and in mass, and poor statistics. Here we present the results of a set of high-resolution two-dimensional simulations starting from gaussian initial conditions1,2. Such a distribution, in which the phases of the Fourier components of the density fluctuations are distributed randomly, is the 'least special' of initial states, and is believed to have a physical origin in quantum noise in the early Universe. By systematically comparing results from simulations in which the power spectra varied but the initial phases were kept the same, we argue that filamentary structure is a general result of nonlinear gravitational evolution, and requires less power on large scales than has often been believed.