The Cosmic Ballet: spinning in the web

Abstract

The exact conversation between Alexander and the gymnosophist is not known, but there are several versions of it in folk tales. 1.1: A glimpse into the unknown 3 The origin of rotation in galaxies remains an important question in the field of galaxy formation as it is not only linked to their morphology but also to the rotation of their host dark matter haloes. The key to answering these questions lies in studying the underlying cosmic web in which galaxies and dark matter haloes form and grow. Within this large-scale network of matter, galaxies stand out as majestic pearls and are spinning in a specific rhythm, resembling swirling ballerinas along the long filamentary strings of matter. This is akin to performing a grand ballet on this gigantic cosmic stage, the cosmic web, making us wonder how all of this has been set into motion. The most prominent example is the disc of our own galaxy, the Milky Way, which is spinning perpendicular to the underlying local web. In this thesis, we investigate how and why galaxies rotate from the point of the view of the large-scale cosmic web. We study how different features of the web influences properties such as spin and shape of galaxies and their dark matter haloes. We find explicit correlations between spin and the host cosmic web components in which they are growing. Ω Λ = Λ 3H 2 0 = 0.691, H 0 = 67.74 km s −1 Mpc −1. These fractions are given with respect to the critical density ρ c = 3H 2 0 8πG , defined as the density for which the Universe is spatially flat. The Hubble parameter H is defined as H =ȧ a where a is the expansion factor and H 0 is the Hub-Here, v is the peculiar velocity, which is the relative velocity of a particle with respect to the Hubble flow, and it is given as: u = Hr + v, (1.6) where u is the total velocity and r = ax. At a certain stage in the structure formation process, the regions of overdensities corresponding to δ > 0 overtake and matter accumulates rapidly in these regions. At this stage, the linear approximation, which is valid for |δ| 1, 1.3: Numerical simulations The simulations are carried out with periodic boundary conditions to account for the cosmological principle that the Universe is homogeneous and isotropic on large scales. The power spectrum for cold dark matter is usually used to initialize a simulation. Positions and velocities are assigned to each dark matter particle and are evolved from a uniform distribution using the linear theory approximation (as described in subsection 1.4.1). This sets up the initial conditions for the simulation. 1.3: Numerical simulations Successes of hydro simulations: The recent decade has seen several large volume simulations that can reproduce surprisingly well many global properties of galaxies, such as the stellar mass function, the bimodality of star-formation rates and colours, and galaxy morphologies. Some of the most studied and most advanced hydrodynamical simulations include: Illustris(Vogelsberger et al. 2014), eagle (Schaye et al. 2015), Horizon AGN (Dubois et al. 2014), Illustris TNG...