FIR Infrared Emission as Indicator of Interaction in Hickson Compact Groups

Due to their very high spatial density and relatively low velocity dispersion, Hickson’s compact groups of galaxies (hereafter HCGs, Hickson et al. 1989a, H89a) are ideal test grounds where to study the physics of galaxy interaction.Tidal shocks induced by galaxy interaction are expected to trigger rapid bursts of star formation in the circumnuclear region of galaxies. The increases in density and temperature caused locally by such shocks produce an enhancement in both the total FIR luminosity and in the ratio between the FIR fluxes at 60 and 100 μm. These enhancements have been actually observed in the circumnuclear regions of both interacting and ”putative” merging galaxies and should therefore be found also in all galactic environments where the frequency of interaction is higher than in the field. However, while interactions are more frequent among HCGs members than in the field (e.g. Hickson 1994, Shaker et al. 1999), there are conflicting arguments on whether HCGs present or do not present a FIR excess. As stressed by many authors, the critical point is the IRAS data resolution which prevents to map the spatial distribution of the FIR emission. We investigate the FIR properties of a selected sample of HCGs by sing the new high spatial resolution data from Allam et al. 1996 (A96). In particular, we address the problem whether or not there is any FIR enhancement in the compact groups and the reasons of that. This is a short presentation of the analysis performed and of the results obtained (Merluzzi et al. 1999).