The cosmic web and the local universe

In this thesis we investigate the characteristics and the time evolution of the matter distribution on Megaparsec scales, which is also known as the Cosmic Web. To undergo our investigation, we introduce the NEXUS and NEXUS+ suite of morphological methods for the segmentation of the Cosmic Web into its distinct components: clusters, filaments, sheets and voids. Compared to previous methods, our techniques perform a more successful and natural detection of morphological environments mostly due to the use of a multiscale and user-free approach.

At high redshift the cosmic web is dominated by thin and short filaments and walls, which merge during the successive evolution, to give rise at present time to a few long and massive structures. The massive haloes are located in cluster and thick filaments, with the remaining components populated by low mass objects. It suggests that these latter structures are difficult to identify in redshift surveys given their sparse sampling with galaxies.

In the second part we investigate the extent to which large scale environment can affect the satellite population of our own galaxy. Milky Way-mass haloes located in the lowest density regions or those in sheet environments have on average significantly fewer substructures. Such an effect does not play an important role for our galaxy since our neighbour, the Andromeda galaxy, excludes the Milky Way from residing in such an environment. The massive satellite population of our galaxy is atypical, with at most 1%
of LCDM haloes having a similar substructure population as the Milky Way.