Observational Gamma-ray Cosmology

Abstract

We discuss how measurements of the absorption of gamma-rays from GeV to TeV energies via pair production on the extragalactic background light (EBL) can probe important issues in galaxy formation. Semi-analytic models (SAMs) of galaxy formation, based on the flat LCDM hierarchical structure formation scenario, are used to make predictions of the EBL from 0.1 to 1000 microns. SAMs incorporate simplified physical treatments of the key processes of galaxy formation -- including gravitational collapse and merging of dark matter halos, gas cooling and dissipation, star formation, supernova feedback and metal production. We will summarize SAM successes and failures in accounting for observations at low and high redshift. New ground- and space-based gamma ray telescopes will help to determine the EBL, and also help to explain its origin by constraining some of the most uncertain features of galaxy formation theory, including the stellar initial mass function, the history of star formation, and the reprocessing of light by dust. On a separate topic concerning gamma ray cosmology, we discuss a new theoretical insight into the distribution of dark matter at the center of the Milky Way, and its implications concerning the high energy gamma rays observed from the Galactic center.

11 pages, 7 figures, to appear in the proceedings of the Gamma 2004 Symposium on High Energy Gamma Ray Astronomy, Heidelberg, July 2004 (AIP Proceedings Series)

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• Ultra High Energy Cosmic Rays from Black Hole Jets of Radio Galaxies
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• Strong New Constraints on the Extragalactic Background Light in the Near- to Mid-IR
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• New Fermi-LAT event reconstruction reveals more high-energy gamma rays from Gamma-ray bursts
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• MAGIC TeV Gamma-Ray Observations of Markarian 421 during Multiwavelength Campaigns in 2006
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• VERITAS Observations of the BL Lac Object PG 1553+113
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• VERITAS Observations of Six Bright, Hard-Spectrum Fermi-LAT Blazars
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• The origin of multi-TeV flares from the nearest blazar Markarian 421
• Observations of Extragalactic Sources with the MAGIC Telescope
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