Islands no more: the important mergers of nearby galaxies and their effects

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Galaxy shapes can change dramatically as galaxies interact and collide with each other. In these collisions, the smaller of the two galaxies is torn to pieces and is spread into a faint ‘stellar halo’ that surrounds the larger of the two galaxies. The larger of the two galaxies survives but can be scarred by the collision. The largest collisions can cause new stars to form and can destroy galaxy disks. This research group at the University of Michigan will combine new observations with computer modeling of the past collisions experienced by nearby, well-studied galaxies. This insight will improve our understanding of galaxy growth, and these methods will be used by other astronomers using huge new datasets from the Vera C. Rubin Observatory. The investigators will measure the positive effects of adding research experiences to large introductory college science courses. If scaled-up to other institutions, this approach has the potential to enhance interest in science and science literacy.During this project, the investigators will use Hyper Suprime-Cam on the Subaru optical telescope in Hawaii. They will construct deep and wide-area maps of the stellar halos and satellite systems of a diverse sample of five galaxies with masses similar to the Milky Way mass. They plan to use these new data and models of galaxy growth to develop new metrics of the collisions experienced by a galaxy. With knowledge of these collisions in hand, they can better understand the long-term effects of these collisions on these five specific galaxies. Importantly, they seek to confirm, or refute, tentative correlations between past collisions and satellite galaxy numbers. These properties may signal important missing ingredients in small-scale cosmology and galaxy formation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.