Abstract
Abstract We searched for redshifted O emission lines from a possible warm-hot intergalactic medium (WHIM) surrounding the cluster of galaxies A2218 at $z=0.1756$ using the X-ray Imaging Spectrometer (XIS) instrument on Suzaku. This cluster is thought to have an elongated structure along the line of sight based on previous studies. We studied systematic uncertainties in the spectrum of the Galactic emission and in the soft X-ray response of the detectors due to the contamination building up on the XIS filters. We detected no significant redshifted O lines, and set a tight constraint on the intensity with upper limits for the surface brightness of O VII and O VIII lines of $1.1 \times 10^{-7}$ and $3.0 \times 10^{-7} \;\mathrm{photons} \;\mathrm{cm}^{-2} \,\mathrm{s}^{-1} \,\mathrm{arcmin}^{-2}$, respectively. These upper limits are significantly lower than the previously reported fluxes from the WHIM around other clusters of galaxies. We also discuss the prospect for detecting the WHIM lines with the Suzaku XIS in the future.
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