Unique characteristics of voids in a complex universe

The ΛCDM model is quite successful in the phenomenological description of the evolution of our Universe and the structures within, even though it relies on two as of yet unknown forms of matter and energy. According to this model, most of the matter in our Universe is in the form of cold dark matter (CDM) and visible structures made up of baryonic matter contain significantly less mass than CDM. The other unknown quantity that drives the latetime accelerated expansion of our Universe is referred to as dark energy. A cosmological constant Λ for this type of energy is so far consistent with observations. The most overdense structures in our Universe have been studied extensively and through their use in observations the ΛCDM model was built. In contrast, the study of the largest and most underdense regions of the cosmic web, known as cosmic voids, emerged only in recent years. While their use as cosmological probes is already well established, there is still a vast space to explore various aspects of their structure and dynamics, as well as to test the validity of predictions from linear theory in these underdense environments. The subject of this dissertation is to test both of these aspects by using state-of-the-art hydrodynamical N-body simulations. The detailed study of voids is not only interesting in its own right, but our results can additionally help in improving current methods employed in cosmological tests with voids, as well as maximize their use across both time and scale. After introducing the topic and summarizing the basics of cosmology in chapters 1 and 2, we describe our methods and simulations in chapters 3 and 4. As the background of this work is covered, we investigate general aspects of void properties and find an alignment of their size distributions on large scales in chapter 5, before exploring the structure and dynamics of tracers around voids through their profiles in chapter 6, where we identify new biases in estimators. These chapters form the foundations for more detailed studies and we find a validity of linear theory predictions on velocities around voids down to scales of only a few megaparsecs in chapter 7. Subsequently, in chapter 8 we explore the necessity of complex hydrodynamical simulations and discover small impacts of baryons on observable void statistics compared to more simple dark matter only simulations. Moreover, we examine the different distributions of CDM and baryons around voids. Lastly, we follow the evolution of voids over nearly the entire age of the Universe in chapter 9, where we analyze the evolution of their common statistics in matter and biased tracers, as well as test theoretical predictions on the growth of structures. Furthermore, we uncover a unique characteristic of voids that makes their evolution appear quite trivial, although reasons for this seem to be rather complex.