  The cluster soft excess emission indicates the presence of large amounts of
warm gas (T ~ 10^6 K) in the neighborhood of galaxy clusters. Among the
clusters that display this phenomenon is the Coma cluster, the nearest rich
galaxy cluster. The excess emission is more prominent at the cluster's
outskirts than at its center. Detailed studies of its large-scale emission --
up to ~2.6 Mpc from the cluster's center -- reveal that these warm baryons are
as massive as, or possibly more massive than, the well-known hot intra-cluster
medium (T ~10^8 K). A possible interpretation of the excess emission from the
Coma cluster is radiation from low-density filaments located in the
neighborhood of the cluster. In this case, the filaments would extend for much
larger distances, or feature higher density, than predicted by current
cosmological simulations.
