Warm-Hot Intergalactic Medium in the Sculptor Supercluster

Abstract

We have analyzed the soft X-ray emission in a wide area of the Sculptor supercluster by using overlapping ROSAT PSPC pointings. After subtraction of the point sources we have found evidence for extended, diffuse soft X-ray emission. We have investigated the nature of such extended emission through the cross-correlation with the density of galaxies as inferred from the Muenster Redshift Survey. In particular we have analyzed the correlation as a function of the temperature of the X-ray emitting gas. We have found a significant correlation of the galaxy distribution only with the softest X-ray emission (0.1--0.3 keV) and only for gas temperatures kT < 0.5 keV. We have excluded that this soft X-ray diffuse emission, and its correlation with the galaxy distribution, is significantly contributed by unresolved AGN, group of galaxies or individual galaxies. The most likely explanation is that the soft, diffuse X-ray emission is tracing Warm-Hot Intergalactic Medium, with temperatures below 0.5 keV, associated with the large-scale structures in the Sculptor supercluster.

8 pages, 6 figures, submitted to MNRAS; Version 2: some major changes due to a bug found in the image analysis code. The main result is unchanged. The paper has been expanded with the discussion about the contribution of single and star-forming galaxies to the diffuse emission, an estimate of the overdensity of the WHIM in the supercluster and with other referee's comments. Abstract slightly changed. Accepted for pubblication in MNRAS