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 (0.81-3.5 keV) and the APM Northern Galaxy Catalog (13.5 < E < 19.0). At zero lag (θ = 0), we detect a 3.5 σ correlation signal with an amplitude of W_(xg)(0) = 0.045 ± 0.013. This signal passes a series of control tests. At non-zero lag (θ > 0), the angular dependence of W_(xg) has two main features: the main signal for θ approx < 4', and an almost flat plateau with an amplitude of W_(xg)(θ approx > 4') approx = 0.015. When fields with galaxy clusters as Einstein targets are removed, the plateau virtually disappears, and the zero-lag amplitude becomes W_(xg)(0) = 0.029 ± 0.013.