X-RAY ABSORPTION BY WHIM IN THE SCULPTOR WALL

We present XMM Reflection Grating Spectrometer (RGS) and Chandra Low-Energy Transmission Grating (LETG) observations of the blazar, H 2356-309, located behind the Sculptor Wall, a large-scale galaxy structure expected to harbor high-density Warm-Hot Intergalactic Medium (WHIM). Our simultaneous analysis of the RGS and LETG spectra yields a 3 sigma detection of the crucial redshifted O VII K alpha line with a column density (greater than or similar to 10(16) cm(-2)) consistent with similar large-scale structures produced in cosmological simulations. This represents the first detection of nonlocal WHIM from X-ray absorption studies where XMM and Chandra data are analyzed simultaneously and the absorber redshift is already known, thus providing robust evidence for the expected repository of the missing baryons.