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This Week at Physics

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Event Number 3473

  Thursday, October 16th, 2014

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
The Extragalactic Gamma-ray Background AND Searching for Satellite Galaxies of the Milky Way in the Dark Energy Survey
Time: 2:30 pm
Place: 5280 Chamberlin
Speaker: Keith Bechtol, University of Chicago
Abstract: Part 1: The extragalactic gamma-ray background (EGB) is generated by the superposition of all extragalactic gamma-ray emissions and therefore provides a window on both the demographics and evolution of non-thermal phenomena across cosmic time. A significant fraction of the total EGB intensity has now been resolved into individual sources using the Fermi LAT, and there is an emerging understanding of how fainter members of the established extragalactic gamma-ray source classes can account for a majority of the residual approximately isotropic component of the gamma-ray sky, called the isotropic gamma-ray background (IGRB). The latest measurement of the IGRB spectrum with the Fermi LAT from 100 MeV to 820 GeV exhibits a high-energy cutoff feature consistent with the attenuation of high-energy gamma rays by pair-production on the IR/optical/UV extragalactic background light. High-energy cosmic neutrinos will be essential to see beyond this gamma-ray horizon to greater distances and higher energies.

Part 2: Targeted searches for indirect dark matter signals in the direction of Milky Way satellite galaxies provide some of the strongest current constraints on the annihilation cross section of dark matter derived from gamma-ray observations. Milky Way satellite galaxies have the advantages of low astrophysical backgrounds, the ability to constrain the dark matter abundance and distribution from the kinematics of member stars, and the opportunity to combine observations of multiple satellites in a joint-likelihood framework to enable more sensitive analyses. Accordingly, the discovery of additional Milky Way satellites in wide-field optical imaging surveys may provide substantial advances for indirect dark matter searches. I will discuss a matched-filter maximum-likelihood algorithm to search for and characterize ultra-faint galaxies in the ongoing Dark Energy Survey, which will cover 5000 square degrees in the relatively less explored south Galactic cap.
Host: Vandenbroucke
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