Shock-induced star cluster formation in colliding galaxies
  We studied the formation process of star clusters using high-resolution N-body/smoothed particle hydrodynamcs simulations of colliding galaxies. The total number of particles is 1.2x10^8 for our high resolution run. The gravitational softening is 5 pc and we allow gas to cool down to \sim 10 K. During the first encounter of the collision, a giant filament consists of cold and dense gas found between the progenitors by shock compression. A vigorous starburst took place in the filament, resulting in the formation of star clusters. The mass of these star clusters ranges from 10^{5-8} Msun. These star clusters formed hierarchically: at first small star clusters formed, and then they merged via gravity, resulting in larger star clusters. 
Takayuki R.Saitoh, Hiroshi Daisaka, Eiichiro Kokubo, Junichiro Makino,   Takashi Okamoto, Kohji Tomisaka, Keiichi Wada, Naok...
astro-ph.CO