Cross-Correlation Between X-Ray and Optical/Near-Infrared Background Intensity Fluctuations

Abstract

Angular power spectra of optical and infrared background anisotropies at wavelengths between 0.5 to 5 µm are a useful probe of faint sources present during reionization, in addition to faint galaxies and diffuse signals at low redshift. The cross-correlation of these fluctuations with backgrounds at other wavelengths can be used to separate some of these signals. A previous study on the cross-correlation between X-ray and Spitzer fluctuations at 3.6 µm and 4.5 µm has been interpreted as evidence for direct collapse blackholes (DCBHs) present at z > 12. Here we return to this cross-correlation and study its wavelength dependence from 0.5 to 4.5 µm using Hubble and Spitzer data in combination with a subset of the 4 Ms Chandra observations in GOODS-S/ECDFS. Our study involves five Hubble bands at 0.6, 0.7, 0.85, 1.25 and 1.6 µm, and two Spitzer-IRAC bands at 3.6 µm and 4.5 µm. We confirm the previously seen cross-correlation between 3.6 µm (4.5 µm) and X-rays with 3.7σ (4.2σ) and 2.7σ (3.7σ) detections in the soft [0.5-2] keV and hard [2-8] keV X-ray bands, respectively, at angular scales above 20 arcseconds. The cross-correlation of X-rays with Hubble is largely anticorrelated, ranging between the levels of 1.4−3.5σ for all the Hubble and X-ray bands. This lack of correlation in the shorter optical/NIR bands implies the sources responsible for the cosmic infrared background at 3.6 and 4.5 µm are at least partly dissimilar to those at 1.6 µm and shorter.

Probing Large-scale Coherence between Spitzer IR and Chandra X-Ray Source-subtracted Cosmic Backgrounds

“…Cappelluti et al (2013) measured a statistically significant cross-power spectrum between the sourcesubtracted Spitzer CIB and Chandra CXB [0.5-2] keV fluctuations in the Extended Groth Strip (EGS), suggesting that sources responsible for the CIB excess share the same environment with, or are, accreting BHs. This result was confirmed by Mitchell-Wynne et al (2016). Neither study was able to probe with high significance the cross-power at the largest scales (i.e., >20-30 ′′ ) arising from clustering.…”

“…Mitchell-Wynne et al 2016). The novelty of our analysis lies in the combination of deeper fields, at both IR and X-ray wavelengths, over a much larger area.…”

“…In total we used 243 Chandra pointings yielding a total of 11.9 Ms of flare-cleaned data, over an area of 0.3 deg 2 (see Table 1). The data analysis methods used have been described in detail in Cappelluti et al (2013) and Mitchell-Wynne et al (2016) except that here we apply a stricter rejection of flares (see Cappelluti et al 2017) and use both the FAINT and VFAINT telemetry mode data.…”

Spectral Properties of Populations Behind the Coherence in Spitzer Near-infrared and Chandra X-Ray Backgrounds

“…There have been a few studies about the coherence between the cosmic X-ray background (CXB) and the CIB (Cappelluti et al 2013;Mitchell-Wynne et al 2016;Cappelluti et al 2017;Li et al 2018). These studies mostly focused on the cross power spectra, which were used to study the possible contributing sources to the cross power.…”

The clustering of undetected high-redshift black holes and their signatures in cosmic backgrounds

“…Moreover, they find an excess of about an order of magnitude at 5σ confidence when com-pared to models for the contribution of the known unmasked source population at z < 7 from Helgason et al (2014). Mitchell-Wynne et al (2016) detected a similar signal in the Chandra Deep Field South. Recently, Li et al (2018) extended and confirmed these results and detected the signal on even larger scales -up to scales of ∼1000"-1500" using the Spitzer-SPLASH survey and the Chandra-COSMOS legacy survey data.…”