Toward First-Principle Simulations of Galaxy Formation: II. Shock-Induced Starburst at a Collision Interface during the First Encounter of Interacting Galaxies

We investigated the evolution of interacting disk galaxies using high-resolution N-body/SPH simulations, while taking into account the multiphase nature of the interstellar medium. In our high-resolution simulations, a large-scale starburst occurred naturally at the collision interface between two gas disks at the first encounter, resulting in the formation of star clusters. This is consistent with observations of interacting galaxies. The probability distribution function (PDF) of the gas density showed a clear change during the galaxy–galaxy encounter. The compression of gas at the collision interface between the gas disks first appears as an excess at nH~$ 10 cm$⁻³$ in the PDF, and then it moves to higher densities ($nH 100 cm⁻³) in a few times 10⁷ years, where starburst takes place. After the starburst, the PDF goes back to a quasi-steady state. These results give a simple picture of starburst phenomena in galaxy–galaxy encounters.