RII Track-4: Making Galaxies Out of An (Ultra) Light Invisible Matter Halo

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Understanding the formation of large-scale structures is one of the most challenging tasks in both observational and theoretical cosmology. When and how did particles -- as we understand them today -- come into existence? How did these particles then go on to produce the large-scale structures familiar from astronomical observations, such as galaxies and the apparent invisible halos around them, commonly called dark matter halos? Our capacity to answer these questions specifically depends on linking the microphysics of dark matter particles to the macrophysics of structure formation at scales larger than galaxies: the dark matter halos in which galaxies form. The dynamic between galaxies and dark matter halos is known as the galaxy-halo connection. Although it is expected that galaxies will subsequently form out of dark matter halos, the galaxy-halo connection is still not well understood. The dynamic between galaxies and dark matter halos is known as the galaxy-halo connection. Using computer simulations, the PI and a trainee will work with KIPAC director and Stanford faculty member Risa Wechsler to produce insights into how observations of the galaxy-halo connection can provide insight into specific dark matter models.While there are many candidates for dark matter, there is no known and observed particle that can adequately explain how dark matter halos and therefore galaxies, form. One extremely promising, yet still hypothetical particle type is a class known as axion-like particles (ALPs). Direct detection experiments are not the only way to constrain the properties of dark matter -- looking at the structures dark matter is expected to form on large scales is another way. The PI will use simulations to test, for the first time, how the microphysics of ALPs leave a unique imprint on the halo occupation distribution function, which describes how galactic matter is distributed throughout the dark matter halo. Our team will simulate the distribution of galaxies in a dark matter halo made only of ALPs to make strong predictions of distinct properties unique to ALP-only halos. The PI is an expert on axion-like particle dark matter theory, while host Risa Wechsler is an expert on computational cosmology, the galaxy-halo connection, and observational cosmology in the optical. Initial steps will include simulations of a boson dark matter field with a publicly available numerical cosmology code that specifically accounts for the quantum pressure associated with axion-like dark matter and can be used to simulate the interactions of multiple subhalos -- correlated with satellite galaxies -- orbiting one central potential, the massive central galaxy.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.