Tracing High-z Galaxies in X-Rays with JWST and Chandra
July 2025 • 2025ApJ...987...40K
Abstract • We leverage James Webb Space Telescope (JWST) data from the COSMOS-Web survey in order to provide updated measurements on the auto-power spectrum of the now resolved cosmic near-infrared background (CIB) and its coherence with the unresolved soft cosmic X-ray background (CXB) observed by Chandra at z > 6. Maps of the CIB in the F277W and F444W NIRCam filters are constructed with sources fainter than mAB = 25 and cross-correlated with the CXB in the [0.5–2] keV band. We find that on scales between 1″ and 1000″ the CIB–CXB cross-power in both NIRCam filters is statistically significant, with signal-to-noise ratios (S/Ns) of 4.80 and 6.20, respectively, from redshifts 0 ≤ z ≤ 13. In our high-z (6 ≤ z ≤ 13) interval we find coherence in both filters, with S/Ns of 7.32 and 5.39, respectively. These results suggest that there are X-ray-emitting galaxies resolved by JWST, including star-forming galaxies and active galactic nuclei. We fit the large-scale biasing of the IR sources producing the CIB as a function of z with results consistent with prior measurements, and place constraints on the CXB flux and biasing at low and high z. The CXB flux measurements presented in this study suggest that approximately 94% of the [0.5–2] keV CXB is resolved, and this value is consistent within 2σ with the complete resolution of the [0.5–2] keV CXB.
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