FIR Observations of Intracluster Dust in Galaxy Clusters

Abstract

Far-infrared (FIR) observations with ISOPHOT aboard the Infrared Space Observatory (ISO) were investigate extended diffuse FIR emission from intracluster dust (ICD) in six galaxy clusters with crossed scans at two wavelengths. Based on IRAS data, M86 has been suggested to have been ram pressure dust stripped during its infall into the Virgo cluster, while in the centers of a few galaxy clusters some evidence for diffuse FIR emission has been found. The ISOPHOT data reveal a complex FIR morphology for M86, with a compact double source near the galaxy center and several offcenter sources. Overall, the FIR data are not consistent with the ram pressure dust stripping scenario, but indicate tidal interactions have a significant influence. The brightest FIR source lies between M86 and the nearby spiral NGC 4402 and represents the first direct detection of a localized intracluster dust cloud not associated with optical or neutral hydrogen emission. Among the six galaxy clusters observed, extended FIR emission, interpreted as thermal emission from intracluster dust, has only been detected in the Coma cluster. Furthermore, the two best candidates for diffuse FIR emission from IRAS are actually strongly affected by foreground cirrus in our Galaxy. Since Coma is a dynamically young cluster with on-going gravitational interactions in the center and infalling galaxy groups, the dust in the ICM is again likely caused by tidal interactions.