WHIM origin for the soft excess emission in the Coma cluster.

This paper provides a new analysis of ROSAT observations of the Coma cluster, to determine the amount of soft X-ray radiation in excess of the contribution from the hot intracluster medium (ICM). The re-analysis is made possible by a high-resolution study of the hot ICM with the XMM–Newton and Planck telescopes out to the cluster's virial radius. The analysis confirms the original findings of a strong excess of soft X-ray radiation, which is likely to be of thermal origin. We find quantitative agreement between the detected soft excess and the physical characteristics of warm–hot intergalactic medium (WHIM) filaments seen in hydrodynamical simulations. We conclude that the most plausible explanation for the soft excess is the presence of ∼10 Mpc long filaments at log  T (K) ≃ 6, with a baryon overdensity of ∼300, converging towards the Coma cluster. This interpretation therefore provides support for the identification of the missing low-redshift baryons with WHIM filaments, as predicted by numerical simulations. [ABSTRACT FROM AUTHOR]