Tidal thickening of galaxy disks
  We have studied a sample of 24 edge-on interacting galaxies and compared them to edge-on isolated galaxies, to investigate the effects of tidal interaction on disk thickening. We found that the ratio h/z of the radial exponential scalelength h to the scale height z is about twice smaller for interacting galaxies. This is found to be due both to a thickening of the plane, and to a radial stripping or shrinking of the stellar disk. If we believe that any galaxy experienced a tidal interaction in the past, we must conclude that continuous gas accretion and subsequent star formation can bring back the ratio h/z to higher values, in a time scale of 1 Gyr. 
Vladimir Reshetnikov (AI SPbSU, Russia), Francoise Combes   (Observatoire de Paris, France)