2003A&A...397..503S

Deep far-infrared (FIR) imaging data obtained with ISOPHOT at 60µm, 90µm, 150µm, and 180µm reveal a complex FIR morphology of the Virgo cluster elliptical M 86 (NGC 4406). A close pair of sources is associated with the centre of the M 86 galaxy and optically discovered dust streamers. Both components have a cold FIR spectrum from the thermal emission of dust with a temperature of ≃18K. A compact off-center source lying ≃3.5' north-west is likely an unrelated background source. The brightest FIR source long-wards of 90µm consists of a compact central core surrounded by an extended halo. It lies close to the nearby spiral galaxy NGC 4402 at the position of the strong northern depression in X-ray brightness. It represents the first detection of an intergalactic dust cloud in the intergalactic region between galaxies. Additionally, three much fainter FIR sources are detected in the field. The ISOPHOT data do not support the earlier suggestion based on IRAS and X-ray data that the unresolved north-western component is cold dust removed from M 86 by ram pressure stripping. The observational evidence suggests that at least for the overall FIR morphology, gravitational interactions between M 86 and neighboring galaxies are much more important than ram stripping of dust. Moreover, the X-ray morphology appears to be partially affected by dusty foreground absorbers. Since M 86 is not showing signs of ongoing stripping of interstellar dust by the intra-cluster medium, a clear case for this dynamical interaction has yet to be found.