The Dynamics of Galaxy Evolution

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Dr Weinberg and his group will examine how galaxies evolve over billions of years, by the collective interactions between their disk, spheroid, and dark-matter halo. The main force acting on these large scales is the mutual gravitational pull of the stars and the dark matter. Galaxies are believed to form by the merger of many smaller units; during this time, gravitational forces vary wildly. Galaxies seen early in cosmic history often have very large bars; the group will explore how these large bars could be produced in this early violent phase. They will then examine how, in the quieter later life of the galaxy, such large bars could shrink to become the shorter and faster-rotating bars seen today. They will also investigate how the disk of stars could become warped and thickened, and how the central bulge might be built up, slowly over cosmic history. In this investigation they will use a combination of perturbation theory, direct integration of stellar orbits, and N-body simulations of several types. To study how gas in the disk affects the galaxy's development, they will combine their N-body code with a code to follow gas dynamics, and will implement a multiple time step algorithm that should increase the simulation throughput by 30 times. The result will be detailed predictions for the motions of stars and gas in present-day galaxies.This award will support a graduate student, and the group will offer research projects to undergraduates, including those in their institution's computer animation group. These students will be trained in numerical and visualization techniques. The group will distribute test suites and tools for their simulation codes, together with reference solutions, to enable other researchers in the field to compare the detailed results of their own codes on the same test problems. They will also produce visualizations and other outreach material from their computations.