Dark matter filaments

Abstract

Present work is a review of extragalactic filament detection and galaxy orientation. Filaments are considered as a part of large-scale structure of Universe since the middle of XX century. The formation of filaments and other elements of large-scale structure was described in Zeldovich theory, which became the base of further computer cosmological simulations. Simulated galaxy distributions are quite suitable for filament detection, but the observations of real galaxies appears much less appropriate for this task. Sloan Digital Sky Survey contains the best data of galaxy distribution for the studies of large-scale structures. Application of different methods of filament detection to SDSS leads to contradictory results. Even morphological analysis of Local Supercluster filaments causes a number of questions. The main complexity of filament search is their composition of mostly dark matter. X-ray images of galaxy clusters supplements optical ones and can help to determine dark matter distribution. Orientation of X-ray halo and optical galaxies in the cluster may point out to the nearest filaments. General analysis of galaxy orientations is needed for the evaluation of this effect. Our review shows models of galaxy cluster at the intersection of filaments and the thread of clusters on the filament. Details of galaxy cluster and filament connections may be revealed after new observations of large-scale structure of Universe and applications new data processing algorithms and cosmological theories of the fluctuation growth.