Cross-correlating cosmic infrared and x-ray background fluctuations: Evidence of significant black hole populations among the cib sources

N. Cappelluti, A. Kashlinsky, R. G. Arendt, A. Comastri, G. G. Fazio, A. Finoguenov, G. Hasinger, J. C. Mather, T. Miyaji, S. H. Moseley

Research output: Contribution to journalArticlepeer-review

56 Scopus citations


In order to understand the nature of the sources producing the recently uncovered cosmic infrared background (CIB) fluctuations, we study cross-correlations between the fluctuations in the source-subtracted CIB from Spitzer/IRAC data and the unresolved cosmic X-ray background from deep Chandra observations. Our study uses data from the EGS/AEGIS field, where both data sets cover an ≃ 8′ × 45′ region of the sky. Our measurement is the cross-power spectrum between the IR and X-ray data. The cross-power signal between the IRAC maps at 3.6 μm and 4.5 μm and the Chandra [0.5-2] keV data has been detected, at angular scales ≳ 20″, with an overall significance of ≃ 3.8σ and ≃ 5.6σ, respectively. At the same time we find no evidence of significant cross-correlations at the harder Chandra bands. The cross-correlation signal is produced by individual IR sources with 3.6 μm and 4.5 μm magnitudes m AB ≳ 25-26 and [0.5-2] keV X-ray fluxes ≪7 × 10-17 erg cm2 s-1. We determine that at least 15%-25% of the large scale power of the CIB fluctuations is correlated with the spatial power spectrum of the X-ray fluctuations. If this correlation is attributed to emission from accretion processes at both IR and X-ray wavelengths, this implies a much higher fraction of accreting black holes than among the known populations. We discuss the various possible origins for the cross-power signal and show that neither local foregrounds nor the known remaining normal galaxies and active galactic nuclei can reproduce the measurements. These observational results are an important new constraint on theoretical modeling of the near-IR CIB fluctuations.

Original languageEnglish (US)
Article number68
JournalAstrophysical Journal
Issue number1
StatePublished - May 20 2013
Externally publishedYes


  • X-rays: diffuse background
  • cosmology: observations
  • dark ages, reionization, first stars
  • infrared: diffuse background
  • stars: Population III

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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