HUNDRED THOUSAND DEGREE GAS IN THE VIRGO CLUSTER OF GALAXIES

The physical relationship between low-excitation gas filaments at ∼104 K, seen in optical line emission, and diffuse X-ray emitting coronal gas at ∼107 K in the centers of many galaxy clusters is not understood. It is unclear whether the ∼104 K filaments have cooled and condensed from the ambient hot (∼107 K) medium or have some other origin such as the infall of cold gas in a merger, or the disturbance of an internal cool reservoir of gas by nuclear activity. Observations of gas at intermediate temperatures (∼105-106 K) can potentially reveal whether the central massive galaxies are gaining cool gas through condensation or losing it through conductive evaporation and hence identify plausible scenarios for transport processes in galaxy cluster gas. Here we present spectroscopic detection of ∼105 K gas spatially associated with the Hα filaments in a central cluster galaxy, M87, in the Virgo Cluster. The measured emission-line fluxes from triply ionized carbon (C IV 1549 Å) and singly ionized helium (He II 1640 Å) are consistent with a model in which thermal conduction determines the interaction between hot and cold phases.