Two disk components from a gas-rich disk-disk merger

We employ N- body, smoothed particle hydrodynamic simulations, including detailed treatment of chemical enrichment, to follow a gas- rich merger that results in a galaxy with disk morphology. We trace the kinematic, structural, and chemical properties of stars formed before, during, and after the merger. We show that such a merger produces two exponential disk components, with the older, hotter component having a scale length 20% larger than the later forming, cold disk. Rapid star formation during the merger quickly enriches the protogalactic gas reservoir, resulting in high metallicities of the forming stars. These stars form from gas largely polluted by Type II supernovae, which form rapidly in the merger- induced starburst. After the merger, a thin disk forms from gas that has had time to be polluted by Type Ia supernovae. Abundance trends are plotted, and we examine the proposal that increased star formation during gas- rich mergers may explain the high alpha-to- iron abundance ratios that exist in the relatively high- metallicity, thick- disk component of the Milky Way.