Emergence of Filamentary Structure in Cosmological Gravitational Clustering

The morphological nature of structures that form under gravitationalinstability has been of central interest to cosmology for over two decades. Aremarkable feature of large scale structures in the Universe is that theyoccupy a relatively small fraction of the volume and yet show coherence onscales comparable to the survey size. With the aid of a useful synthesis ofpercolation analysis and shape statistics we explore the evolution ofmorphology of isolated density clumps in {\it real space} and that of thecluster distribution as a whole in scale-invariant cosmological models ofgravitational instability. Our results, based on an exhaustive statisticalanalysis, indicate that at finite density thresholds one-dimensional filamentsare more abundant than two-dimensional sheets (pancakes) at most epochs and forall spectra although the first singularities could be pancake-like. Bothfilamentarity and pancakeness of structures grow with time (in scale-freemodels this is equivalent to an increase in resolution) leading to thedevelopment of a long coherence length scale in simulations.Comment: 8 pages, latex, 3 figures; To appear in ApJ Let