The search for dark matter annihilation in galaxy clusters at VERITAS
Recent data and cosmological models point to a significant fraction of the Universe being comprised of Cold Dark Matter (DM), though little is known about it directly as it does not interact electromagnetically. The most likely explanation for DM is a Weakly Interacting Massive Particle (WIMP) having a mass as low as ∼10 GeV to as high as ∼10 TeV. WIMPs are believed to be their own antiparticles and self-annihilate into a variety of lighter particles including γ-rays. Many direct detection, indirect detection, and direct production schemes have been proposed to search for the elusive WIMP. Galaxy clusters, consisting of hundreds to thousands of galaxies, are the largest collections of matter in the Universe held together by gravity. As such, galaxy clusters also contain the highest concentrations of DM found anywhere. This thesis presents results on the VERITAS observations of 12 galaxy clusters selected from archival data. We seek to detect the γ-rays originating from the DM interactions within galaxy clusters. We calculate astrophysical J-factors for each of the galaxy clusters six of which had no prior J-factors with the DM simulations package CLUMPY. Since a DM detection is not made, the limit to the thermally-averaged DM annihilation velocity-weighted cross-section is then computed from the γ-ray flux upper limit. We employ a stacking method to combine the limits of the 12 galaxy clusters. The limits from the stacking method are found to be less constraining than some individual galaxy clusters due to the wide range of limits considered. We conclude that a larger number of galaxy clusters in the stacking method will yield more competitive limits to other DM searches.
Finley, Purdue University.
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