The kinematics of warm clouds in cooling flows; a case for turbulence

Small amounts of warm, ionized gas are observed in the centres of many clusters of galaxies with cooling flows. We investigate the properties of these clouds of gas and, in particular, their ability to survive in the harsh environment of the intracluster medium. The widths of the optical emission lines from these clouds indicate relative motions of up to 1000 km s–1, which easily leads to the destruction of clouds unless their properties are in a fairly narrow range. We suggest that the hot gas in the flow is turbulent and that this is responsible for much of the observed velocity spread. Wave motions and noise associated with the turbulence can also provide a source of heating of the warm parts of the clouds through plasma slip.