However, stripping of the gaseous component of spirals occurs in clusters, with consequences far more drastic than those of the tidal encounters in groups. Stripping appears to be associated primarily with the presence of a pervasive ICM, which acts on the interstellar gas via ram pressure or conductive processes. The analysis of H I deficiency in cluster galaxies is a delicate business demanding both optical and 21-cm data of high quality. The number of clusters studied in the 21-cm line is still relatively small, and the identification of statistical trends only tentative. Aperture synthesis observations with long integration times will be necessary in order to extend the sample of observed clusters beyond the redshift limits currently accessible to filled-aperture instruments.
Much work remains to be done in the Virgo cluster .
Further investigation is necessary to confirm the correlation between H I deficiency, the velocity relative to the cluster as a whole, at the density of the intergalactic gas. Observations of integrated CO will provide an indication of the fate of the clumpier molecular gas.