1210.5302 (N. Cappelluti et al.)

Cross-correlating cosmic IR and X-ray background fluctuations: evidence of significant black hole populations among the CIB sources    [PDF]

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

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.

View original: http://arxiv.org/abs/1210.5302