Resolving the extragalactic hard X-ray background

R. F. Mushotzky, L. L. Cowie (), A. J. Barger and K. A. Arnaud
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R. F. Mushotzky: NASA Goddard Space Flight Center
L. L. Cowie: Institute for Astronomy, University of Hawaii
A. J. Barger: Institute for Astronomy, University of Hawaii
K. A. Arnaud: NASA Goddard Space Flight Center

Nature, 2000, vol. 404, issue 6777, 459-464

Abstract: Abstract The origin of the hard (2–10 keV) X-ray background has been a mystery for over 35 years. Most of the soft X-ray background has been resolved into individual sources (mainly quasars), but these sources do not have the spectral energy distribution required to match the spectrum of the X-ray background as a whole. Here we report the results of a deep survey, using the Chandra satellite, in which the detected hard X-ray sources account for at least 75 per cent of the hard X-ray background. The mean X-ray spectral energy distribution of these sources is in good agreement with that of the background. Moreover, most of those hard X-ray sources are associated unambiguously with either the nuclei of otherwise normal bright galaxies, or with optically faint sources. The latter could be active nuclei in dust-enshrouded galaxies or a population of quasars at extremely high redshift.

Date: 2000
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DOI: 10.1038/35006564

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