Galaxies and non-galactic baryons in cosmic filaments

Doctoral theses defended at the University of Tartu, summary in Estonian

Galaxies are some of the most interesting objects visible in the sky. They have different shapes, from cartwheel or CD-like disky spirals to featureless egg-shaped ellipticals. One hundred years ago the distances of galaxies were first measured and it became apparent that they are collections of stars at vast distances from us. Even the Sun is located within a galaxy, the Milky Way, which is just one of billions of other galaxies in our universe. Sky surveys with telescopes have measured exact positions of galaxies. From these we know that galaxies are not situated randomly, but in preferred configurations. Some are in dense associations, clusters. Clusters are connected by long chains of galaxies, filaments. There are regions where there are very few or no galaxies at all, voids. This configuration can be imagined as similar to human populations on Earth, where the clusters are big cities, filaments highways with nearby towns and the voids regions of sparse inhabitation. It has also been determined that galaxies differ based on the density of their environ- ment. In clusters galaxies are more likely in a later stage of evolution: larger and older. Voids in contrast are territories of small young galaxies. Filaments are intermediate, where many different types of galaxies are found. Filaments also inhabit a variety of environments, inside voids and between dense clusters. The goal of this thesis is to characterise galaxies in filaments. It is still not well unders- tood how the filament environment affects the evolution of galaxies. In order to gain insight into this problem we utilised publicly available observational data and the expertise of the scientists at the Tartu University Tartu Observatory in identifying galaxy configurations. As the result of this work we found that galaxies in filaments are less star forming and general- ly more evolved than would be expected based on density alone. However more research is needed to fully understand the nature of galaxies.