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Deciphering the gamma-ray background: stafrorming galaxies, AGN, and the search for Dark Matter in the GeV Band.

Deciphering the gamma-ray background: stafrorming galaxies, AGN, and the search for Dark Matter in the GeV Band. Vasiliki Pavlidou Einstein Fellow. Shin’ichiro Ando (Caltech) Brandon Hensley (Caltech) Luis Reyes (U. Chicago) Jennifer Siegal-Gaskins (Ohio State) Tonia Venters (Goddard).

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Deciphering the gamma-ray background: stafrorming galaxies, AGN, and the search for Dark Matter in the GeV Band.

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  1. Deciphering the gamma-ray background: stafrorming galaxies, AGN, and the search for Dark Matter in the GeV Band. Vasiliki PavlidouEinstein Fellow Shin’ichiro Ando (Caltech) Brandon Hensley (Caltech) Luis Reyes (U. Chicago) Jennifer Siegal-Gaskins (Ohio State) Tonia Venters (Goddard)

  2. 4 days of Fermi LAT Credit: LAT collaboration The gamma-ray sky

  3. What is making the GeV isotropic diffuse background? • Guaranteed sources: active galaxies, starforming galaxies • Hypothesized source classes: starburst galaxies, galaxy clusters, dark matter cusps

  4. VP & Fields 02, Ando & VP 09 Learn about B-fieldat high-z! What physics can we learn about galaxies? • How galaxies make gamma rays: • Gas makes stars • Stars blow up and make supernova remnants • Supernova remnants accelerate cosmic rays • Cosmic rays collide with gas, make pions, • Pions decay into gamma rays • How much diffuse gamma-ray emission due to all galaxies, everywhere, ever? Physics input to this calculation: • Cosmic star formation history (how much star formation, gas) • Cosmic-ray -- gas interactions • Cosmic-ray acceleration, confinement, escape

  5. Credit: J. Buckley 1998 (Science),illustration: K. Sutliff VP & Venters 08 Venters, Reyes & VP 09 What physics can we learn about AGN? • How AGN make gamma rays: • Gamma-ray loud AGN (blazar) has relativistic jet aimed at you • Some disturbance (?) accelerates electrons (?) to relativistic energies • Relativistic electrons Compton-upscatter soft photons (synchrotron? accretion disk? rescattered from broad line region?)to GeV energies • How much diffuse gamma-ray emission due to all AGN, everywhere, ever? Physics input to this calculation: • Luminosity function • Energy spectrum • Duty cycle • Extragalactic UV, optical, IR backgrounds! More input parameters, more complicated problem, less understood physics, fewer well-constrained inputs But also: more observables, more potential for discovery!

  6. Time passes, structure forms, density cusps develop, annihilation rate should be higher @ cusps! (Kolb 98) Why look for dark matter in -rays? Bang!

  7. Siegal-Gaskins & Pavlidou 2009, PhysRevLett.102.241301, arXiv:0901.3776 1GeV 10 GeV Siegal-Gaskins 08 Where do we look for DM with -rays? Where should we be looking? Individual sources: • Galactic Center (but: messy) • Nearby low-gas dwarf galaxies (but: faint) • Nearby MW substructure clumps (but: where?) Unresolved emission (isotropic diffuse): • Contribution from MW halo substructure, extragalactic sources • But: astrophysical foregrounds! DM signal could be subdominant… If only we could somehow enhance a subdominantDM signal…

  8. Siegal-Gaskins & Pavlidou 2009 PhysRevLett.102.241301, arXiv:0901.3776 Can we enhance a subdominant DM signal? Yes, we can! Take into account information about angular anisotropies • MW subhalos: few, nearby, lots of power at small scales • Blazars: many, faraway, very little power at small scales • There should be a transition in angular power at small scales as we move from low E (no DM) to high E (some DM)

  9. How well can we do? Preliminary Hensley, Siegal-Gaskins & Pavlidouin preparation

  10. How much can we learn? Preliminary We could measure the annihilation spectrum! Hensley, Siegal-Gaskins & Pavlidouin preparation

  11. Conclusions • A wealth of information on high-energy processes is encoded in the isotropic diffuse background in GeV energies starforming galaxies, blazars, dark matter(+ galaxy clusters, starburst galaxies, …) • A dark matter signal from the Milky Way substructure could be hiding in the isotropic diffuse background:More substructure away from Galactic center, where clumps are not tidally disrupted  collective unresolved clump emission appears isotropic • The DM signal can be robustly separated from other astrophysical contributions by combining spectral and anisotropy information • DM particle mass, annihilation spectrum can be recovered • Fermi is performing spectacularlyThe future is bright, stay tuned!

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