We have used the Hubble Space Telescope and Wide Field Planetary Camera 2 to image the putative tidal dwarf galaxy located at the tip of the Southern tidal tail of NGC 4038/9 , the Antennae .
We resolve individual stars , and identify two stellar populations .
Hundreds of massive stars are present , concentrated into tight OB associations on scales of 200 Â pc , with ages ranging from 2 - 100 Â Myr .
An older stellar population is distributed roughly following the outer contours of the neutral hydrogen in the tidal tail ; we associate these stars with material ejected from the outer disks of the two spirals .
The older stellar population has a red giant branch tip at I = 26.5 \pm 0.2 from which we derive a distance modulus ( m - M ) _ { 0 } = 30.7 \pm 0.25 .
The implied distance of 13.8 \pm 1.7 Mpc is significantly smaller than commonly quoted distances for NGC 4038/9 .
In contrast to the previously studied core of the merger , we find no super star clusters .
One might conclude that SSCs require the higher pressures found in the central regions in order to form , while spontaneous star formation in the tail produces the kind of O-B star associations seen in dwarf irregular galaxies .
The youngest population in the putative tidal dwarf has a total stellar mass of \approx 2 \times 10 ^ { 5 } M _ { \odot } , while the old population has a stellar mass of \approx 7 \times 10 ^ { 7 } \leavevmode \nobreak M _ { \odot } .
If our smaller distance modulus is correct , it has far-reaching consequences for this proto-typical merger .
Specifically , the luminous to dynamical mass limits for the tidal dwarf candidates are significantly less than 1 , the central super star clusters have sizes typical of galactic globular clusters rather than being 1.5 times as large , and the unusually luminous X-ray population becomes both less luminous and less populous .