Cross-correlating cosmic IR and X-ray background fluctuations: evidence of significant black hole populations among the CIB sources. (arXiv:1210.5302v1 [astro-ph.CO])

Cross-correlating cosmic IR and X-ray background fluctuations: evidence of significant black hole populations among the CIB sources. (arXiv:1210.5302v1 [astro-ph.CO]):
In order to understand the nature of the sources producing the recently
uncovered CIB fluctuations, we study cross-correlations between the
fluctuations in the source-subtracted Cosmic Infrared Background (CIB) from
Spitzer/IRAC data and the unresolved Cosmic X-ray Background (CXB) from deep
Chandra observations. Our study uses data from the EGS/AEGIS field, where both
datasets cover an ~8'x45' region of the sky. Quantitatively, our measurement is
the cross-power spectrum between the IR and X-ray data which we detect to be
statistically significant and positive at angular scales >20" where the
source-subtracted CIB fluctuations in the Spitzer data are dominated by the
clustering component. The cross-power signal between the IRAC maps at 3.6 um
and 4.5 um and the Chandra [0.5-2] keV data has been detected with the overall
significance of ~3.5 sigma and ~5 sigma 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 um and
4.5 um magnitudes m_AB>25-26 and [0.5-2] keV X-ray fluxes <<7x10^-17 cgs. We
determine that at least 15-25% of the large scale power of 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 the accreting black
holes than among the known populations. We discuss the various possible low-
and high-z suspects for the discovered cross-power and show that neither local
foregrounds, nor the known remaining normal galaxies and active galactic nuclei
(AGN) can reproduce the measurements. These observational results are an
important new constraint on theoretical modeling of the near-IR CIB
fluctuations.