Ph.D Thesis

Ph.D StudentAriel Keselman
SubjectTowards a Better Paradigm of Galaxy Formation
DepartmentDepartment of Physics
Supervisor Full Professors Nusser Adi
Full Thesis textFull thesis text - English Version


In this thesis I present several studies of topics at the forefront of galaxy formation theory, first within the framework of the standard cosmological scenario, LCDM, and then including an extension acting over galactic scales. The first study deals with the mechanisms by which regions neighboring a galaxy affect its history of mass assembly (assembly bias). In this study we develop a novel technique designed to avoid highly non-linear dynamics, and use a suite of cosmological simulations to show that assembly bias is imprinted at very early stages of galaxy formation. We show also that haloes tend to form earlier in regions initially collapsing along a single dimension, i.e. planar collapse. The next study deals with the formation mechanisms of galactic bulges with disk-like features (i.e. pseudo-bulges). We perform several high-resolution, star forming hydrodynamical simulations of major mergers of identical pure-disc galaxies, and analyze them with an observational approach. We show that highly coherent rotation of stellar particles in the remnants core is a common outcome of major mergers of gas rich disc galaxies. These cores are made of young stars formed in the main merger star-burst. This result could greatly ease tension between recent observations of our galactic neighborhood and bulge-formation theory. Last, I present two studies of an extension to

CDM, which we term ReBEL (daRk Breaking Equivalence principle). In this scenario, a long-range force acts only between non-baryonic particles, in addition to gravity, and at scales below galactic. The most distinctive feature in ReBEL is that galactic structure forms faster, resulting in a recent quiescent epoch at the galactic level, allowing galaxies to form giant thin disks. We study the implications at a cosmological level, reproducing the observed two-point correlation function, and Lya power spectrum, and at a galactic scale, reproducing observed satellite patterns such as the Sagittarius stellar stream. On galactic scales ReBEL predicts the existence of orphan streams with large pericentric radii, and the absence of significant DM mass in the core of the Sgr stellar stream. On cosmological scales it predicts that baryonic mass in galaxies and groups of galaxies should be correlated to their total mass, and should be lower than

what is expected in the standard cosmological scenario. It also predicts a lower halo density in void regions.