engleski

Simulation and Visualization of Selfgravitating N-particle System

When we observe the universe we see structures on essentially all scales. The large distribution of matter in the universe as traced by galaxy structures shows a complex irregular pattern, characterized by clusters of galaxies which are organized in filaments around large voids.The most widely used tool to study these structures is by means of gravitational N-body simulations1. During simulation, the structures form and evolve from a given initial state (generally unknown) according to the law of Newtonian gravity. The long-range character of the gravity, however, produces several peculiarities in satistical behaviors of the system that are totally different from usual systems.These are the ensembles inequivalence, negative specific heat, non-extensive thermodynamics, strong dependence on N, large fluctuations, self-consistent chaos, slow relaxation, and formation of structures. Some years ago adetailed two point correlation analysis of galaxy clustering2 showed that galaxy correlation properties are similar to those of a fractal, self-similar object with fractal dimension D ~ 2. Since the evidence for scale-invariance of highly irregular galaxy distributions with large structures and voids strongly depends on the appropriate choice of two point correlation analysis, we studied various two point correlation estimators to find that only Ripley's K-function minus estimator gives the correct fractal dimension of an arbitrary 3-d disrtibution of point particles. The test is performed first on the Menger's sponge model with a known fractal distribution of point particles, for which we also developed a small 3-d visualization program RoPo (Rotate Points)3. K-minus estimator was then applied to 2dF (Two-Degree Field) catalogue data.

galaxy structure; galaxy correlations; selfgravitating N-particle system; fractal dimension

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