Detection and nature of cold intra-group gas in compact group environments

We present the results of our 21cm GBT-VLA study discovering a significant diffuse neutral intra-group medium (IGM) (on an average 39% of the total HI mass) in a sample of 22 Hickson Compact Groups (HCGs). HCGs are dense concentrations of galaxies where strong tidal interactions constantly change gas distribution and morphology of the member galaxies. HCGs have been found to be deficient in HI, although our new GBT detections have reduced the previously estimated deficiency values considerably. The GBT detected broad HI wings rather than discrete features, suggesting the presence of a fainter HI component over a large velocity range. Here we present the comparison between the HI detected by the GBT (single dish) and the VLA (interferometer), which resulted in our discovery. Comparing the instrumental properties of the two instruments, we conclude that the excess HI is in the form of a diffuse neutral intra-group medium, that is most likely being fed by the inter-stellar medium of the individual galaxies. We also found correlations between the percentage of excess gas in these systems to their HI deficiency, Hubble type of the central or dominant galaxy and their evolutionary stage, all of which advocates the gradual dispersion of the tidally stripped neutral gas into the IGM with group evolution.