| dc.description.abstract | Galaxy formation theory encompasses a wide range of physical mechanisms that contribute to the growth and evolution of galaxies. First, we study the present-day connection between galaxy morphology and angular momentum using the DARK SAGE semi-analytic model of galaxy formation. We find that not only do bulge-dominated galaxies tend to live in halos with higher dark matter specific angular momentum than disk-dominated galaxies, but intermediate galaxies (those with roughly equal fractions of bulge and disk mass) have the lowest dark matter specific angular momentum of all. Yet, when controlling for halo mass, rather than stellar mass, the relationship between dark matter specific angular momentum and morphology vanishes. Based on these results, we find that halo mass—rather than angular momentum—is the main driver of the predicted morphology sequence. These results drove my interest in understanding the galaxy-halo connection. In particular, when looking at the stellar mass-halo mass relation, DARK SAGE galaxies have significantly large scatter in stellar mass at fixed halo mass. Empirical models have not been able to fully constrain this scatter. In addition, semi-analytic models like DARK SAGE systematically predict higher stellar mass scatter at fixed halo mass than hydrodynamical simulations. To further investigate the physical origin of this scatter, we explore modifications to the black hole physics in DARK SAGE. Our experiments show that, turning off AGN feedback reduces the stellar mass scatter significantly. Changing the black hole seeding and AGN feedback prescription reduces the scatter in stellar mass at all halo mass bins, except at halo masses above 10^14. Taken together, these results suggest that the AGN feedback in SAMs acts in a qualitatively different way than AGN feedback implemented in cosmological simulations. This means that either or both may require substantial modification to match the empirically-determined scatter. | |
