Dark matter in the dwarf galaxy II Zwicky 40

H I observations of the blue compact dwarf galaxy II Zwicky 40 at high angular resolution reveal the presence of two kinematical systems. The H I structure and kinematics can be understood in terms of two interacting H I clouds, each cloud consisting of about 2×108M_sun; of neutral gas. The optical emission is located at the centre of the northern cloud and might be the result of recent star formation which is triggered by the interaction. The authors estimate total masses of order 3×109M_sun; for each cloud. This exceeds the visible mass by an order of magnitude and indicates the presence of dark matter in II Zwicky 40.