Hi, Steve.

There's this... I thought it was interesting:

Huge New Part Of Milky Way Rotates Backwards.

And this:

Astronomers Find Proof That Milky Way Has A Hot Corona.

I like your idea that what we're seeing in the halo of M83 and even our own Milky Way could be the results of the last collision and abundant gases may tend to follow that path. I wonder if (Atomic)Hydrogen behaves that way in the halos of most galaxies.

I can understand why globular clusters at the outer reaches of our Milky Way or other galaxies can be 'old' since they could be remnants of galaxy collisions. Seems that hydrogen gas/ISM is not as abundant in some areas to produce new stars. Also could a galaxy's bowshock contribute to star formation? I would think so.

Maybe it's a combination.