On the FIR emission from intracluster dust

We make predictions for the diffuse far-infrared (FIR) emission from dust i n the intracluster medium (ICM) of the Virgo cluster using detailed informa tion on potential dust sources, grain heating and sputtering rates availabl e for this cluster from recent optical and X-ray studies. In the cluster co re we identify the winds of red giant and supergiant IC stars as the main c ontinuous sources of IC grains, with a dust injection rate of 0.17 M(circle dot)yr(-1). The predicted FIR surface brightness from this dust component is however a factor of similar to 10 below the detection limit of currently available telescopes. Grains that are impulsively removed from spiral gala xies by ram-pressure stripping as they enter the cluster core region can sp oradically dominate the grain injection rate into the ICM. However, these e vents should lead to the appearance of rare, relatively bright, localised F IR sources around the parent galaxy. The outer regions of dynamically young clusters like the Virgo cluster have a further potential source of intracluster grains since they are still acc reting freshly infalling spiral galaxies which are presumably contained in an accreting intergalactic medium (IGM). We show that cosmics ray driven wi nds from the infalling spirals can inject grains into a subvirial IGM that is external to the observed X-ray-emitting ICM. Sputtering during the injec tion process and in the IGM is weak, so that the injected grains should acc umulate in the IGM until the infall brings them into contact with the hot I CM. Normalising the mass lass rate in the galactic winds to the mass-loss r ate and B-band luminosity of the Milky Way, we estimate a dust accretion ra te of 1.0 M(circle dot)yr(-1) from the infalling IGM. This effect dominates the dust injection rate from known sources embedded in the hot Virgo ICM. Thus, any detection of diffuse IR emission would probe the current dust acc retion rate for the cluster, acting as an indicator of the youth and the dy namical state of the cluster. The predictions for the Virgo cluster are gen eralised to other clusters and the possibility of detection of dynamically young clusters at cosmological distances is discussed. Although dominated b y the discrete source emission from galactic disks, it is possible that dif fuse sub-mm dust emission from the ICM could be detected in experiments sim ilar to those designed to map the sub-mm excess due to the Sunyaev-Zeldovic h effect in distant clusters.