Cold gas in the intracluster medium: implications for flow dynamics and powering optical nebulae

We show that the mechanical energy-injection rate generated as the intracluster medium (ICM) flows around cold clouds may be sufficient to power the optical and near-infrared emission of nebulae observed in the central regions of a sample of seven galaxy clusters. The energy-injection rate is extremely sensitive to the velocity difference between the ICM and cold clouds, which may help to explain why optical and infrared luminosity is often larger than expected in systems containing active galactic nuclei. We also find that mass recycling is likely to be important for the dynamics of the ICM. This effect will be strongest in the central regions of clusters where there is more than enough cold gas for its evaporation to contribute significantly to the density of the hot phase.