Aharonian, F. and Akhperjanian, A. G. and Bazer-Bachi, A. R. and Beilicke, M. and Benbow, W. and Berge, D. and Bernlöhr, K. and Boisson, C. and Bolz, O. and Borrel, V. and Braun, I. and Breitling, F. and Brown, A. M. and Chadwick, P. M. and Chounet, L. M. and Cornils, R. and Costamante, L. and Degrange, B. and Dickinson, H. J. and Djannati-Ataï, A. and Drury, L. O. and Dubus, G. and Emmanoulopoulos, D. and Espigat, P. and Feinstein, F. and Fontaine, G. and Fuchs, Y. and Funk, S. and Gallant, Y. A. and Giebels, B. and Gillessen, S. and Glicenstein, J. F. and Goret, P. and Hadjichristidis, C. and Hauser, D. and Hauser, M. and Heinzelmann, G. and Henri, G. and Hermann, G. and Hinton, J. A. and Hofmann, W. (2006) 'A low level of extragalactic background light as revealed by big gamma-rays from blazars.', Nature., 440 (7087). pp. 1018-1021.
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 light1. An alternative approach2, 3, 4, 5 is to study the absorption features imprinted on the -ray spectra of distant extragalactic objects by interactions of those photons with the background light photons6. Here we report the discovery of -ray emission from the blazars7 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 galaxies8. 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 formed9. This result also indicates that intergalactic space is more transparent to -rays than previously thought.
|Keywords:||High-energy photons, MKN 501, Telescope, Space, Absorption, H1426+428, Spectrum, Universe, Stars, 2Mass.|
|Full text:||(NA) Not Applicable |
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|Publisher Web site:||http://dx.doi.org/10.1038/nature04680|
|Date accepted:||22 February 2006|
|Date deposited:||No date available|
|Date of first online publication:||April 2006|
|Date first made open access:||No date available|
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