Kinematics and morphology of ionized gas in Hickson Compact Group 18

We present new observations of $H\alpha $ emission in the Hickson Compact Group 18 (HCG 18) obtained with a scanning Fabry-Perot interferometer. The velocity field does not show motions of individual group members but, instead, a complex common velocity field for the whole group. The gas distribution is very asymmetric with clumps of maximum intensity coinciding with the optically brightest knots. Comparing $H\alpha $ and HI data we conclude that HCG 18 is not a compact group but instead a large irregular galaxy with several clumps of star formation.