Can the unresolved X-ray background be explained by the emission from the optically-detected faint galaxies of the GOODS project?

M. A. Worsley, A. C. Fabian, F. E. Bauer, D. M. Alexander, W. N. Brandt, B. D. Lehmer

Research output: Contribution to journalArticle

27 Scopus citations

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.

Original languageEnglish (US)
Pages (from-to)1735-1741
Number of pages7
JournalMonthly Notices of the Royal Astronomical Society
Volume368
Issue number4
DOIs
StatePublished - Jun 1 2006

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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