Cosmological Simulation Studies of the Intrinsic Alignment of Galaxies

Weak lensing refers to a statistical study of the small distortions of the images of galaxy shapes due to the gravitational deflection of light by the foreground structures. Weak lensing has emerged as a powerful probe to constrain cosmological paramters to subpercent errors in future cosmological surveys. However, the intrinsic alignment of galaxies with the large-scale density field is a significant astrophysical contaminant in weak lensing measurements that can bias cosmological constraints and also a useful probe of galaxy formation and evolution. Recent large volume hydrodynamic simulations that include galaxy formation have become an important tool to study intrinsic alignments which are difficult to model analytically and the presence of baryonic component allows us to directly measure galaxy shapes and alignments. This thesis presents a study of the intrinsic alignment of galaxies in the MassiveBlack-II (MBII) hydrodynamic simulation. We first analyze the shapes and alignments of the stellar component of the galaxies in MBII and their dependence on subhalo mass and environment. This is followed by an analyis of two-point statistics quantifying intrinsic alignmnents and their scaling with mass, luminosity and color. We then compare the galaxy shapes and alignments in the hydrodynamic simulation with the shapes of dark matter subhalos in a dark matter-only simulation performed with the same resolution and initial conditions. Finally, we analyze the intrinsic alignments of disks and elliptical galaxies which are morphologically classified based on a dynamical bulge disk decomposition in MBII and Illustris, a hydrodynamic simulation implemented with moving mesh code and different baryonic feedback models. We also carry out a parameter space study by modifying the free paramters in the MBII feedback models and study their impact on intrinsic alignments using small volume simulations.