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Content archived on 2022-12-23

The physical nature of large- and superlarge-scale structure in the Universe

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The formation of large-scale structure in the Universe is one of the most fundamental questions, touching as it does on the question of man's existence. The visual observations of chains or filaments of galaxies, or the BoötesVoid or the Great Wall, with huge sizes of hundreds of millions of light years, have had a great impact, scientifically and publicly. They reveal that galaxies trace out a structure of filaments and sheets or walls, confirming spectacularly the theoretical work of the Russian school of Zel'dovich, Doroshkevich, Shandarin and others. As large-scale structure has formed through gravitational instability, the physical elements characteristic of the velocity field in the Universe are filaments, which we identify as large-scale structure, and those of the gravitational potential field sheets, superlarge-scale structure. Then, just as star and galaxy counts play a central role in astronomy, so the most basic physical parameters here are the counts or number densities of filaments and sheets. Other physical parameters are their thickness, the distribution and flow of galaxies within these structures and the numbers of knots or rich clusters of galaxies. This project is based on the direct measurement of these quantities. The long-term aim is to make accurate physical measurements of the densities of filaments and sheets, to determine their evolution with time, and to relate these measurements to the physical characteristics of the underlying velocity and gravitational potential fields in the Universe. A method based on one-dimensional cluster analysis has been developed for the analysis of pencil beam galaxy redshift surveys. A thorough investigation will be made of the method by also applying it to both galaxy and dark matter catalogues resulting from dynamically numerical simulations, which are being made for this purpose by the Potsdam team. The method will also be tested on simulations of Durham theoretical cosmologists done for their own entirely different purposes. The Russian team is also developing associated analysis based on 2- and3-dimensional cluster analysis. An aim is the analysis of the Durham/UKST FLAIRsurvey to B of 17m of a 75degrees x 20degrees area in the south now being compiled. In the longer term, the Durham team will have even deeper redshift data from the coming 2-degree field for the Anglo-Australian telescope. Application to QSO absorption spectra will address the question of evolution.

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