Gas Dynamics in Galaxy Mergers
  In interacting and merging galaxies, gas is subject to direct hydrodynamic effects as well as tidal forces. One consequence of interactions is the rapid inflows of gas which may fuel starbursts and AGN. But gas dynamics is not limited to inflows; a small survey of equal-mass and unequal-mass encounters produces a wide variety of features, including plumes between galaxies, extended disks formed by infall of tidal debris, and counterrotating nuclear disks. An even richer spectrum of behavior awaits better thermodynamic models for gas in merging galaxies. 
Joshua E. Barnes