Collaborative Research: Exploring the Dark Side of NGC 5128

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The investigators will study the outskirts of the nearest giant elliptical galaxy, named Centaurus A, to learn how the galaxy built up its stellar and dark matter mass over cosmic time. The investigators have measured the positions of nearly all the luminous star clusters associated with Centaurus A, and will precisely measure their velocities using large ground-based telescopes. Using observations of the collection of star clusters, and their motions around Centaurus A, the investigators will measure the dark matter density profile of the galaxy, and search for remnants of smaller galaxies that have merged with Centaurus A. The important goal of their observations is identifying large star clusters which are the remnants left over from smaller galaxies after they have been devoured by the larger Centaurus A. By studying the motions of these star clusters in detail, along with the smaller galaxies it has destroyed, they will have a complete inventory of the 'dark side' of Centaurus A. Their results will be applied to studies of all galaxy populations. The investigators will present the science results from this program to visitors at the National Science Foundation's Kitt Peak National Observatory, by implementing a new docent training program at the visitor center. The investigators will travel to Bryce Canyon National Park and present their results, through summer internships, which ultimately teach 16,000 visitors about the night sky.The currently favored cold dark matter model makes clear predictions for the sub-halo mass function and dark matter density profile of galaxy-sized halos, but quantitatively verifying these predictions is challenging. Centaurus A's dark matter density profile will be measured, using the kinematics derived from a nearly complete sample of star clusters, and the results compared to recent simulations that suggest galaxies with recent mergers and active galactic nuclei should have shallow dark matter profiles. By combining the star cluster kinematics with an already existing red giant branch star map, the visible, accreted substructures will be identified and weighed. Finally, a complete sample of ultra-compact dwarfs will be analyzed, including a search identifying them as the central compact remnants of stripped dwarf galaxies. Accounting for this population of sub-halos is a novel aspect of this program, and one that has largely been neglected when testing galaxy formation models. These efforts will test major predictions of the cold dark matter model at sub-galactic scales in our nearest elliptical galaxy neighbor.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.