Galaxy mergers viewed from angular momentum

Ok so here’s a question that’s bugging me, and I’ve asked it on Galaxy Zoo and Quora already but perhaps someone here can provide a general accepted solution;

How do galaxies shed enough energy to make mergers possible (in terms of conservation of angular momentum)?

One answer from MLPeck at GZ proposes dynamical friction as solution. Other answers (also from astronomers) simply state ‘the mutual gravity’ makes it happen but that seems a bit like a non-answer to me, mutual gravity doesn’t make (relative) kinetic energy magically disappear.

A little background info if needed; the mergers of neutron stars / black holes we’ve been hearing about are only possible because the system of orbiting objects are losing energy straight into spacetime in the form of gravitational waves. If this didn’t happen they would not merge! They would be orbiting each other forever.

So how does this work for galaxies, what are the generally accepted mechanisms here keeping in mind conservation of angular momentum?

Dynamical friction as proposed by mlpeck at Galaxy Zoo it is then;