Previous abstract Next abstract

Session 47 - Microlensing.
Display session, Tuesday, January 16
North Banquet Hall, Convention Center

[47.01] The Spatial Structure of the Cosmic X-Ray Background: Correlation with Local Galaxies and Gravitational Lensing by Clusters.

A. Refregier, D. J. Helfand (Columbia U.), A. Loeb (Harvard U.), R. G. McMahon (Cambridge)

We investigate two contributions to the spatial structure of the Cosmic X-ray Background (CXB). We first study the contribution of the local universe to the CXB by correlating 67 Einstein X-ray fields (.1--3.5 keV) with the APM galaxy catalog (E<19). We compute the two point correlation function W_xg both at zero lag and at nonzero-lag. We detect a >3 \sigma correlation signal. We test the validity of our results by using various control data sets. Slicing the galaxy catalog into various magnitude intervals allows us to examine the contribution of different redshift shells. The energy dependence is studied by computing W_xg in the softer and harder band. By fitting the amplitude and the angular dependence of W_xg, we investigate the contribution to the CXB of the catalogued galaxies themselves and of X-ray sources spatially associated with them.

Gravitational lensing by intervening matter could also affect the spatial structure of the CXB. We focus on the lensing effect of clusters of galaxies on the apparent distribution of point sources which make up most (if not all) of the CXB. We model the clusters as Singular Isothermal Spheres and consider three reasonable extensions of the \log N-\log S relation observed by ROSAT. By setting a flux threshold for the resolution of point sources, we consider both the number counts of resolved sources and the intensity of the unresolved component of the CXB. We find that both of these quantities are significantly affected by the lensing effect within a narrow ring located at the critical radius of the cluster. We show that the effect could be detectable by AXAF. Aside from constraining models of the CXB, this lensing effect could be used to probe the potential of clusters of galaxies.

This work was supported by NASA under grant NAGW 2507.

Program listing for Tuesday