Hi Mike, Re our conversation about the preservation of relative
position in the potential during mergers, Milosavljevic & Merritt 2001
is vaguely relevant. Fig. 1 implies the BHs are about 0.1 galactic half
mass radii from each other within about 5 galaxy crossing times. Although
the tree code they've used to model the early stages of the merger involves
some smoothing out, it's not clear how much this is driven by collisional
effects. Maybe this does need to be looked at in the collisionless limit....

     Cheers,  Cathie