Cosmological Applications of Filamentary Structures in the Universe

Abstract

The formation and evolution of filamentary structures involve the actions of the<br/> dark sector and gravitational law. At the same time, a filament is an important environment<br/> through which gas and matter accrete and subhalos infall onto its member<br/> galaxies (halos). In this thesis, we present studies on filamentary structures in two<br/> contexts, one for filament as a probe to constrain cosmological models and the other<br/> for studying the effects of filaments on its halos and galaxies. In Part 1, we presented<br/> how the shapes of filaments change depending on cosmological models. We identified<br/> large-scale filaments from dark matter halos of cosmological simulations of various cosmological<br/> models including ΛCDM, a branch of dynamic dark energy, and a branch of<br/> modified gravity. It is found that filaments in the ΛCDM universe are straighter than<br/> those in the other models. We also found that the discriminations of the alternative<br/> models from ΛCDM and between themselves are possible with the straightness evolution<br/> of filaments. By finding the dependence of filament straightness on underlying<br/> cosmology, we suggest the straightness of filaments as a complimentary cosmological<br/> test. In Part 2, we studied the roles of filaments in the galaxy (halo) formation and<br/> evolution. First, we examined the dependence of substructure abundance of clusters<br/> on filament straightness. Clusters in straighter filaments are found to have fewer substructures<br/> even when the contribution of the mass and formation time of halo, and<br/> the number of clusters in filament are minimized. On the other hand, we also studied<br/> the correlation between void galaxy luminosity and straightness of void filament. It<br/> was found that void galaxies are brighter in straighter void filaments. Based on these<br/> findings, we conclude that filaments influence on their galaxies (halos) by controlling<br/> subhalo infall and mass accretion onto galaxies (halos). Physical interpretations of our<br/> results, as well as their cosmological implications are presented.