We assess the possibility to detect the warm-hot intergalactic medium (WHIM) in emission and to characterize its physical conditions and spatial distribution through spatially resolved X-ray spectroscopy, in the framework of the recently proposed DIO
S, EDGE, Xenia, and ORIGIN missions, all of which are equipped with microcalorimeter-based detectors. For this purpose we analyze a large set of mock emission spectra, extracted from a cosmological hydrodynamical simulation. These mock X-ray spectra are searched for emission features showing both the OVII K alpha triplet and OVIII Ly alpha line, which constitute a typical signature of the warm hot gas. Our analysis shows that 1 Ms long exposures and energy resolution of 2.5 eV will allow us to detect about 400 such features per deg^2 with a significance >5 sigma and reveals that these emission systems are typically associated with density ~100 above the mean. The temperature can be estimated from the line ratio with a precision of ~20%. The combined effect of contamination from other lines, variation in the level of the continuum, and degradation of the energy resolution reduces these estimates. Yet, with an energy resolution of 7 eV and all these effects taken into account, one still expects about 160 detections per deg^2. These line systems are sufficient to trace the spatial distribution of the line-emitting gas, which constitute an additional information, independent from line statistics, to constrain the poorly known cosmic chemical enrichment history and the stellar feedback processes.
We studied the high temperature plasma in the direction of the Sculptor supercluster at z=0.108 with Suzaku. Suzaku carried out four observations in the supercluster: namely, A2811, A2811 offset, A2804, A2801 regions in 2005 Nov.--Dec., including the
regions beyond the virial radii of these clusters. The study needed precise background estimation because the measured intensity of the redshifted lines, especially those from oxygen, were strongly affected by the the Galactic emission. The spectra taken in the regions outside of the virial radii of the member clusters were used as the background which included both the Galactic and Cosmic X-ray Background (CXB) components. We also used the background data which were taken near the Sculptor supercluster. Temperature and metal abundance profiles were determined to the virial radii of the member clusters, and then we searched for the oxygen line emission in the region outside of the virial radii of the clusters. As a result, the temperature of the clusters decreased toward the virial radii, and the spectral fits for the filament region did not require extra component other than the Galactic and CXB components. We constrained the intensities of O VII and O VIII lines to be less than 8.1 and 5.1 photons cm^-2 s^-1 arcmin^-2, respectively, as 2-sigma upper limits. The intensity of O VII indicates n_H < 1.6e-5 cm^-3 (Z/0.1 Z_solar)^-1/2 (L/25 Mpc)^-1/2, which corresponds to an over density, delta < 60 (Z/0.1 Z_solar)^-1/2 (L/25 Mpc)^-1/2.
The results from Suzaku XIS observations of the relaxed cluster of galaxies Abell2052 are presented. Offset pointing data are used to estimate the Galactic foreground emission in the direction to the cluster. Significant soft X-ray excess emission ab
ove this foreground, the intra-cluster medium emission, and other background components is confirmed and resolved spectroscopically and radially. This excess can be described either by (a) local variations of known Galactic emission components or (b) an additional thermal component with temperature of about 0.2 keV, possibly associated with the cluster. The radial temperature and metal abundance profiles of the intra-cluster medium are measured within sim 20 in radius (about 60% of the virial radius) from the cluster center . The temperature drops radially to 0.5-0.6 of the peak value at a radius of sim 15. The gas-mass-weighted metal abundance averaged over the observed region is found to be 0.21 +- 0.05 times solar.
About half of the baryons in the local Universe are thought to reside in the so-called warm-hot intergalactic medium (WHIM) at temperatures of 0.1-10 million K. Thermal soft excess emission in the spectrum of some cluster outskirts that contains OVII
and/or OVIII emission lines is regarded as evidence of the WHIM, although the origin of the lines is controversial due to strong Galactic and solar system foreground emission. We observed the Coma-11 field, where the most prominent thermal soft excess has ever been reported, with Suzaku XIS in order to make clear the origin of the excess. We did not confirm OVII or OVIII excess emission. The OVII and OVIII intensity in Coma-11 is more than 5 sigma below that reported before and we obtained 2 sigma upper limits of 2.8 and 2.9 photons cm^-2 s^-1 sr^-1 for OVII and OVIII, respectively. The intensities are consistent with those in another field (Coma-7) that we measured, and with other measurements in the Coma outskirts (Coma-7 and X Com fields with XMM-Newton). We did not confirm the spatial variation within Coma outskirts. The strong oxygen emission lines previously reported are likely due to solar wind charge exchange.
