Spin Flips: Variation in the Orientation of Dark Matter Halos over their Merger Histories

Abstract

Semi-analytic models of galaxy formation typically form the spheroidal components of galaxies ("bulges"), solely through galactic major mergers. However, it is possible that non-merger events (e.g. a "fly-by" by a smaller halo) can perturb a galaxy--halo system sufficiently to form a bulge. We present a preliminary investigation into the frequency of major changes in halo and galaxy spin direction, which could be signatures of such events.