Detailed Analysis of the Cross-Correlation Function between the X-Ray Background and Foreground Galaxies

摘要

Recent ROSAT surveys suggest that galaxies can constitute the new class of faint sources required to explain the full phenomenology of the cosmic X-ray background (XRB). To test this hypothesis without resorting to optical identifications, we compute the two-point cross-correlation function (CCF) estimator W_xg(θ) between 62 Einstein IPC fields (0.813.5 keV) and the APM Northern Galaxy Catalog (13.5 < E < 19.0). At zero lag (θ = 0), we detect a 3.5 σcorrelation signal with an amplitude of W_xg(0) = 0.045 ± 0.013. This signal passes a series of control tests. At nonzero lag (θ > 0), the angular dependence of W_xg has two main features: the main signal for θ≤4_, and an almost flat plateau with an amplitude of W_xg(θ ≥4_) ≈0.015.