Collaborative Research: Starless Dark Matter Halos as a Definitive Test of Dark Matter Models

University Of California-Irvine, Irvine CA

Investigators

Abstract

Over the last 40 years, a large number of astronomical observations have provided overwhelming evidence that approximately 80% of the mass-density in the universe is in the form of dark matter. The leading theory for dark matter posits that it is made up of as-of-yet undiscovered elementary particles of nature, particles that are significantly more massive than the proton and have very weak interactions with normal matter of the type that makes up the earth and the sun and appears on the periodic table of elements. Importantly, the leading theory - known as Cold Dark Matter - makes concrete predictions for the way dark matter should be clustered and clumped in the space between visible galaxies. Gravitational lensing is a technique that can potentially detect these clumps. If they are detected and quantified as predicted it would provide the most compelling evidence yet that the Cold Dark Matter exists. If not, then this would be a major discovery that calls into question the leading theory of dark matter. This project aims to make unprecedentedly accurate predictions of the clustering and clumping of Cold Dark Matter structures and to interpret ongoing efforts to utilize gravitational lensing as a test of dark matter models. The proposal will also facilitate student training in high-performance computing, data analysis, and quantitative reasoning, all of which are vital to future economic vitality of the nation. The PIs will also devote considerable effort towards high school teacher development, URM outreach programs, and public science talks. This proposal uses cosmological simulations with an unparalleled combination of volume and resolution to rigorously quantify properties of low-mass (M < 107 Msun) dark matter halos. In the standard LCDM cosmological model these halos are predicted to be starless and nearly baryon-free. Gravitational detection of such dark matter structures would be revolutionary, as it would immediately and definitively exclude all models that explain observed mass discrepancies through modifications of Newtonian (or Einsteinian) gravity. It would also rule out all models of dark matter with truncated power spectra at this scale (e.g., the most popular Warm Dark Matter models). The proposed work will provide predictions necessary to take full advantage of upcoming gravitational lensing studies aimed at constraining the number and properties of starless halos. The predictions rely on high resolution, large cosmological volumes, and the inclusion of baryonic physics to properly account for subhalo disruption, baryonic mass loss at reionzation, and other dynamical feedback on the small halos under study. 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.