Search for x-ray emission associated with the Shapley supercluster with Suzaku

Abstract

Suzaku performed observations of 3 regions in and around the Shapley supercluster, a region located between A 3558 and A 3556, at ∼0.9 times the virial radii of both clusters, and two other regions at 1° and 4° away from the first pointing. The 4°-offset observation was used to evaluate the Galactic foreground emission. We did not detect significant redshifted Oxygen emission lines (O VII and O VIII) in the spectra of all three pointings, after subtracting the contribution of foreground and background emission. The upper limit for the redshifted O VIII K? line intensity of the warm-hot intergalactic medium (WHIM) is 1.5 × 10-7 photons s-1 cm -2 arcmin-2, which corresponds to an overdensity of ∼380 (Z=0.1 Z⊙--1/2 (L=3Mpc)-1/2, assuming T = 3 × 106K. We found excess continuum emission in the 1°-offset and on-filament regions, represented by thermal models with kT ∼ 1 keV and ∼2keV, respectively. The redshifts of both 0 and that of the supercluster (0.048) are consistent with the observed spectra. The ∼ 1 keV emission can also be fitted with Ne-rich Galactic (zero redshift) thin thermal emission. The radial intensity profile of the 2 keV component suggests contributions from A 3558 and A 3556, but with significant steepening of the intensity slope in the outer region of A 3558. Finally, we summarized the previous Suzaku search for the WHIM, and discussed the feasibility of constraining the WHIM. An overdensity of < 400 could be detectable using O VII and O VIII emission lines in a range of 1.4 × 106 K < T < 5 × 106 K or a continuum emission in a relatively high-temperature range of T > 5 × 106 K with the Suzaku XIS. The non-detection with Suzaku suggests that a typical line-of-sight average overdensity is <400.