A gamma-ray determination of the Universe’s star formation history
Links to Fileshttps://science.sciencemag.org/content/362/6418/1031
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Type of Work5 pages
Citation of Original PublicationOjha, R.; A gamma-ray determination of the Universe’s star formation history; Science 362(6418), pp. 1031-1034 (2018); https://science.sciencemag.org/content/362/6418/1031
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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
The light emitted by all galaxies over the history of the Universe produces the extragalactic background light (EBL) at ultraviolet, optical, and infrared wavelengths. The EBL is a source of opacity for gamma rays via photon-photon interactions, leaving an imprint in the spectra of distant gamma-ray sources. We measured this attenuation using 739 active galaxies and one gamma-ray burst detected by the Fermi Large Area Telescope. This allowed us to reconstruct the evolution of the EBL and determine the star formation history of the Universe over 90% of cosmic time. Our star formation history is consistent with independent measurements from galaxy surveys, peaking at redshift z ~ 2. Upper limits of the EBL at the epoch of reionization suggest a turnover in the abundance of faint galaxies at z ~ 6.
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