Dynamics of cloud collisions in gaseous disks of galaxies

Abstract

A crucial question in the formation and evolution of galaxies is how the gas in them transforms into stars. In general, HI gas transforms into molecular gas, then collapses to form stars. However, theoretically, the formation of stars is induced by instabilities provided by different agents (e.g., gravitational instability, feedback process, etc.). Several previous works studied the effect of these processes on star formation. However, the collision between the clouds in their orbits could possibly play an important role, which has not been studied before in detail. Due to their epicyclic motions, the clouds at different radii would cross each other’s orbits leading to collisions. By solving their equations of motion, we have calculated the precise orbits of clouds in the galactic disk of NGC 6946, NGC 7331 and NGC 5055 and quantified the collision rates. We show that a significant amount of collisions can influence star formation significantly, especially in LSB or XUV galaxies, where the low-mass stellar disks cannot provide the necessary instability.