UGC-7636 AND NGC-4472 - TIDAL INTERACTION BETWEEN A STRIPPED DWARF IRREGULAR AND A GIANT ELLIPTIC GALAXY

We present new B and I CCD and H I observations of the system in the Virgo Cluster composed of the dwarf irregular galaxy UGC 7636 and the giant elliptical galaxy NGC 4472. These observations strongly suggest that both ram-pressure and tidal stripping have occurred in this system. The H I gas between the two galaxies has been stripped from UGC 7636. Its M(H I)/L(B) ratio is 0.26 M./L(B)., in the range observed for dwarf irregulars. Ram-pressure stripping of the H I gas from the dwarf is suggested by the large velocity width (DELTAv50 approximately 110 km s-1) of the spatially extended H i envelope. The presence of a red optical tidal tail and countertail in the dwarf, with the same colors as the stars in the dwarf's outer regions, as well as a disturbed morphology in the dwarf's inner parts, are evidence for tidal interaction between the two galaxies.