A triggering mechanism for enhanced star formation in colliding galaxies

Abstract

A physical mechanism is proposed for explaining the origin of the intense burst of massive-star formation seen in colliding/merging, gas-rich, field spiral galaxies. The different parameters for the two main mass components, H2 and HI, of the interstellar medium within a galaxy are taken into account, and their consequent different evolution during a collision between two galaxies is followed. It is shown that the massive-star formation created by the Giant Molecular Clouds (GMCs) is increased following a collision between galaxies. During a typical collision between two field spiral galaxies, the H I clouds from the two galaxies undergo collisions at a relative velocity of about 300 km/s. GMCs, with their smaller volume-filling factor, do not collide.