The extragalactic background light and the gamma-ray opacity of the universe |
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| Institution: | 1. Observational Cosmology Lab., Code 665, NASA Goddard Space Flight Center, Greenbelt, MD 20771, United States;2. Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, United States;1. Applied Nuclear Science, School of Physics A28, University of Sydney, NSW 2006, Australia;2. Kernchemie Institute, Philipps-Universität, 35032 Marburg, Germany;3. Joint Institute of Power and Nuclear Research-Sosny NASB, 220109 Minsk, Belarus;4. Joint Institute for Nuclear Research, Dubna, Moscow Region 141980, Russian Federation;1. Skobeltsyn Institute of Nuclear Physics MSU, Leninskie Gory GSP 1, Moscow 119992, Russia;2. Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propogation (IZMIRAN), Russian Academy of Sciences, Troitsk, Moscow region 142092, Russia;1. Instituto de Física Corpuscular (IFIC), CSIC-Universitat de València, Apartado de Correos 22085, E-46071 Valencia, Spain;2. Institute for Particle Physics Phenomenology (IPPP), Department of Physics, Durham University, Durham DH1 3LE, United Kingdom;1. Centre for Space Research, North-West University, Potchefstroom 2520, South Africa;2. Astronomical Observatory of Ivan Franko National University of L''viv, vul. Kyryla i Methodia, 8, L''viv 79005, Ukraine;3. Astrophysical Institute, Department of Physics and Astronomy, Ohio University, Athens, OH 45701, USA |
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| Abstract: | The extragalactic background light (EBL) is one of the fundamental observational quantities in cosmology. All energy releases from resolved and unresolved extragalactic sources, and the light from any truly diffuse background, excluding the cosmic microwave background (CMB), contribute to its intensity and spectral energy distribution. It therefore plays a crucial role in cosmological tests for the formation and evolution of stellar objects and galaxies, and for setting limits on exotic energy releases in the universe. The EBL also plays an important role in the propagation of very high energy γ-rays which are attenuated en route to Earth by pair producing γ–γ interactions with the EBL and CMB. The EBL affects the spectrum of the sources, predominantly blazars, in the ～10 GeV–10 TeV energy regime. Knowledge of the EBL intensity and spectrum will allow the determination of the intrinsic blazar spectrum in a crucial energy regime that can be used to test particle acceleration mechanisms and very high energy (VHE) γ-ray production models. Conversely, knowledge of the intrinsic γ-ray spectrum and the detection of blazars at increasingly higher redshifts will set strong limits on the EBL and its evolution. This paper reviews the latest developments in the determination of the EBL and its impact on the current understanding of the origin and production mechanisms of γ-rays in blazars, and on energy releases in the universe. The review concludes with a summary and future directions in Cherenkov Telescope Array techniques and in infrared ground-based and space observatories that will greatly improve our knowledge of the EBL and the origin and production of very high energy γ-rays. |
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