Arp 119: A High Speed Galaxy Collision with Episodic Star Formation
  Colliding galaxies are excellent laboratories for studying galactic evolution and global star formation. Computer simulations of galaxy collisions, in which at least one galaxy has a significant gaseous component, show the production of density enhancements and shock waves in the interstellar medium. These high-density regions coincide with the locations of recent, large-scale star formation in observations of some real colliding galaxies. Thus, combined n-body/hydrodynamic computer simulations can be used to explore the history and conditions of star forming regions in colliding galaxies. The galaxy system Arp 119 (CPG 29) contains a southern member, Arp 119S (Mrk 984), that has an extremely disturbed appearance, and a northern member, Arp 119N, a gas-poor elliptical. The morphology of both members can be fit well by a simulation in which a gas-rich disk galaxy has been impacted by an equal mass elliptical that had a trajectory approximately perpendicular to the plane of the disk and passed through the disk slightly off-center. We compare multi-wavelength observations of the Arp 119 system with a combined n-body/SPH simulation of colliding galaxies. We find that the progression of recent, large-scale star formation in this galaxy can be accounted for by a single, outwardly propagating collision-induced density wave in the gas. 
Nathan C. Hearn (1), Susan A. Lamb (1 and 2) ((1) Center for   Theoretical Astrophysics - Department of Physics - University...