A low level of extragalactic background light as revealed by gamma-rays from blazars

Nature
F AharonianS J Wagner

Abstract

The diffuse extragalactic background light consists of the sum of the starlight emitted by galaxies through the history of the Universe, and it could also have an important contribution from the 'first stars', which may have formed before galaxy formation began. Direct measurements are difficult and not yet conclusive, owing to the large uncertainties caused by the bright foreground emission associated with zodiacal light. An alternative approach is to study the absorption features imprinted on the gamma-ray spectra of distant extragalactic objects by interactions of those photons with the background light photons. Here we report the discovery of gamma-ray emission from the blazars H 2356 - 309 and 1ES 1101 - 232, at redshifts z = 0.165 and z = 0.186, respectively. Their unexpectedly hard spectra provide an upper limit on the background light at optical/near-infrared wavelengths that appears to be very close to the lower limit given by the integrated light of resolved galaxies. The background flux at these wavelengths accordingly seems to be strongly dominated by the direct starlight from galaxies, thus excluding a large contribution from other sources-in particular from the first stars formed. This result also indicates that i...Continue Reading

Citations

Feb 13, 2007·Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences·Paula M Chadwick
Jun 28, 2008·Science·UNKNOWN MAGIC CollaborationJ Zapatero
Apr 14, 2016·Royal Society Open Science·Asantha Cooray
Apr 21, 2006·Nature·Piero Madau
Mar 24, 2006·Molecular Microbiology·Erwin G ZoetendalWillem M de Vos
May 21, 2010·Physical Review Letters·Warren EsseyJohn F Beacom
Dec 1, 2018·Science·UNKNOWN Fermi-LAT Collaboration
Jun 12, 2012·Physical Review Letters·Arnaud DeLavallaz, Malcolm Fairbairn
Jan 6, 2007·Science·Felix Aharonian

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