Probing large scale coherence between Spitzer IR and Chandra X-ray source-subtracted cosmic backgrounds

TL;DR

This study detects a significant large-scale cross-correlation between the infrared and X-ray cosmic backgrounds, suggesting contributions from early black holes and other sources beyond known populations.

Contribution

It provides the first high-significance detection of large-scale cross-power between IR and X-ray backgrounds and compares observations with models, revealing an excess unexplained by known sources.

Findings

First detection of IR-X-ray cross-power on large scales >20 arcsec

Significant excess over known source models by about an order of magnitude

Possible implications for early black hole populations and cosmic structure

Abstract

We present new measurements of the large scale clustering component of the cross-power spectra of the source-subtracted Spitzer-IRAC Cosmic Infrared Background (CIB) and Chandra-ACIS Cosmic X-ray Background (CXB) surface brightness fluctuations. Our investigation uses data from the Chandra Deep Field South (CDFS), Hubble Deep Field North (HDFN), EGS/AEGIS field and UDS/SXDF surveys, comprising 1160 Spitzer hours and $\sim$ 12 Ms of Chandra data collected over a total area of 0.3 deg$^2$. We report the first ($>$5$\sigma$) detection of a cross-power signal on large angular scales >20 arcsec between [0.5-2] keV and the 3.6 and 4.5$\mu$m bands, at $\sim$5$\sigma$ and 6.3$\sigma$ significance, respectively. The correlation with harder X-ray bands is marginally significant. Comparing the new observations with existing models for the contribution of the known unmasked source population at $z<$7, we find an excess of about an order of magnitude at 5$\sigma$ confidence. We discuss possible interpretations for the origin of this excess in terms of the contribution from accreting early black holes, including both direct collapse black holes and primordial black holes, as well as from scattering in the interstellar medium and intra-halo light.