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Constraining Dark Matter Physics with Cosmological Simulations

  • Author(s): Elbert, Oliver Dewitt
  • Advisor(s): Bullock, James S
  • et al.

Dark Matter (DM) accounts for the vast majority of mass in the universe, but the particle identity of dark matter remains a mystery. Uncovering the fundamental nature of DM remains one of the greatest challenges facing modern physics. Because the only information about DM comes from astrophysical observations, these are the best sources to constrain models. Dwarf galaxies present an especially tantalizing regime to investigate dark physics, as they have the highest ratio of dark to luminous matter and therefore will be most affected by differences between DM models. Additionally, this is precisely the scale where generic dark matter theories have the most difficulty reproducing astronomical observations, leading to the missing satellites, core-cusp and too-big-to-fail (TBTF) problems.

A particular class of models with nuclear scale self-interactions (called SIDM) has emerged as a promising candidate. SIDM naturally forms cored halos, which may alleviate both the core-cusp and TBTF problems. However, at larger scales the the interplay between SIDM halos and the galaxies residing in them is poorly understood, complicating this picture greatly. In this thesis I present numerical simulations of SIDM and CDM halos investigating these issues. I show that at dwarf scales SIDM cross sections as small as $0.5~\cmg$ solve the TBTF and core-cusp problems, and that cross sections 2 orders of magnitude larger are not ruled out. I have also embedded gravitational potentials that approximate realistic galaxies in simulations of larger haloes in order to test the impact of galaxy formation on SIDM halos. These simulations show that SIDM is indistinguishable from CDM in systems where the galaxy dominates the central region, but in galaxies with higher mass-to-light ratios or less centrally concentrated baryons it is possible to constrain SIDM cross sections. In the galaxy cluster regime I show that an SIDM cross section of $0.1-0.2~\cmg$ is preferred to CDM or other SIDM cross sections.

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