UC Irvine

Dark matter drives structure formation of the universe from the largest to smallest scales, yet we lack a complete understanding of its fundamental nature. Self-interacting dark matter, a compelling alternative to cold dark matter, is well motivated by particle physics and impacts the density profiles of dark matter halos, particularly at the centers of low-mass (∼ 1010 M⊙) halos. I use novel cosmological simulations of low-mass halos in SIDM models with moderate (1 − 5 cm2/g) to large (30 − 140 cm2/g) self-interaction cross-sections to analyze the gravothermal evolution of subhalos and isolated halos. I find that moderate cross-sections are not sufficient to produce subhalos with core densities large enough to host the densest Milky Way dwarf spheroidal galaxies. This motivates larger cross-sections that induce gravothermal collapse in such systems. When simulating isolated halos with large cross-sections in cosmological environments, I find that while some halos undergo gravothermal collapse, others experience a delay in gravothermal collapse, driven by mergers. How massive and radial a merger is, and also how frequent mergers are affect the time it takes a halo to reach gravothermal collapse. These findings indicate that accounting for mergers is essential when modeling gravothermal collapse in low-mass halos, since they influence constraints on the SIDM parameter space. This work will impact future research on self-interacting dark matter models, allowing for more robust predictions of dark sector models.