HI observations of interacting galaxy pair NGC 4038/9

We present the results of new radio interferometer Hi line observations for the merging galaxy pair NGC 4038/9 ('The Antennae'), obtained using the Au stralia Telescope Compact Array. The results improve substantially with res pect to those of van der Hulst and show in detail the two merging galactic discs and the two tidal tails produced by their interaction. The small edge -on spiral dwarf galaxy ESO 572-G045 is also seen near the tip of the south ern tail, but distinct from it. It shows no signs of tidal interaction. The northern tidal tail of the Antennae shows no HI connection to the discs an d has an extension towards the west. The southern tidal tail is continuous, with a prominent HI concentration at its tip, roughly at the location of t he tidal dwarf galaxy observed optically by Mirabel, Dottori & Lutz. Clear velocity structure is seen along the tidal tails and in the galactic discs. Radio continuum images at 20 and 13 cm are also presented, showing the dis cs in detail.