Can the unresolved X-ray background be explained by the emission from the optically-detected faint galaxies of the GOODS project? |
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| Authors: | M A Worsley A C Fabian F E Bauer D M Alexander W N Brandt B D Lehmer |
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| Institution: | Institute of Astronomy, Madingley Road, Cambridge CB3 0HA;Department of Astronomy, Columbia University, 538 W 120th Street, New York, NY 10027, USA;Department of Astronomy and Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University Park, PA 16802, USA |
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| Abstract: | The emission from individual X-ray sources in the Chandra Deep Fields and XMM – Newton Lockman Hole shows that almost half of the hard X-ray background above 6 keV is unresolved and implies the existence of a missing population of heavily obscured active galactic nuclei (AGN). We have stacked the 0.5–8 keV X-ray emission from optical sources in the Great Observatories Origins Deep Survey (GOODS; which covers the Chandra Deep Fields) to determine whether these galaxies, which are individually undetected in X-rays, are hosting the hypothesized missing AGN. In the 0.5–6 keV energy range, the stacked-source emission corresponds to the remaining 10–20 per cent of the total background – the fraction that has not been resolved by Chandra . The spectrum of the stacked emission is consistent with starburst activity or weak AGN emission. In the 6–8 keV band, we find that upper limits to the stacked X-ray intensity from the GOODS galaxies are consistent with the ∼40 per cent of the total background that remains unresolved, but further selection refinement is required to identify the X-ray sources and confirm their contribution. |
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| Keywords: | surveys galaxies: active galaxies: starburst X-rays: diffuse background X-rays: galaxies |
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