Dark matter and gas concentrations in the NGC 4532 DDO 137 system

H I synthesis mapping of NGC 4532 and DDO 137, a pair of Sm galaxies on the edge of the Virgo Cluster, is used to determine rotation curves for each o f the galaxies and to resolve the structure and kinematics of three distinc t H I concentrations embedded in an extended envelope of diffuse H I discov ered in earlier Arecibo studies of the system. The H I masses of the three concentrations do not appear to be sufficient for them to be self-gravitati ng; however, their H I masses and dynamical masses are very similar to thos e of faint Im galaxies in the Virgo Cluster. The peak H I column density of each of the clouds is close to the star formation threshold, but CCD image s in B and R reveal no trace of stars or star formation. If the system is g ravitationally bound and in virial equilibrium, we find its total mass to b e 10 times that within the outermost H I contours of the individual galaxie s and clouds. Thirty-seven percent of the total H I lies outside the bounda ries of the individual galaxies as determined by the VLA mapping; 28% canno t be ascribed to either galaxy or to the discrete concentrations. One possi ble way to account for the velocity held and the large quantity of diffuse gas is to assume that DDO 137, the gas concentrations, and other apparent t idal features are due to gas infall into clumps within the dark matter pote ntial of the group, and that prior to the interaction the group consisted o f an irregular galaxy (NGC 4532) and a large, star-poor H I cloud like H I 1225 + 01.