GAS-DYNAMICS AND STAR FORMATION IN INTERACTING AND MERGING GALAXIES

In this paper we describe several additional simulations to those described in Olson and Kwan. We consider the effects various parameters have on the interaction of two galaxies and on the gas cloud collisions which are induced to occur. Increasing the angle of inclination between the spin axis of the galaxy which contains gas clouds and the orbital angular momentum vector, decreasing the mass of the perturbing galaxy, and increasing the kinetic energy of the interaction all have the effect of reducing the perturbation. A case where both galaxies contain gas clouds and the galaxies merge was also studied. As in Olson and Kwan, most of the cloud-cloud collisions which are induced by the interaction are disruptive and a large number of massive clouds is usually not produced. Based on these calculations and those described in Olson and Kwan, we suggest that if the burst of star formation triggered by the interaction of two galaxies occurs near closest approach, it may be related to the large number of disruptive cloud-cloud collisions which are induced. Monitoring the amount of gas mass involved in these collisions allows us to estimate the star-formation rate and the luminosity of the galaxy. We find that the parameters considered here can, to a large degree, account for the broad range of observed ratios of the far-infrared luminosity to molecular gas mass in interacting and merging galaxies. We also show that the radial location of the enhanced star formation depends on these parameters and that, while a large fraction of interacting galaxies which possess strong morphological peculiarities have elevated rates of star formation in or near their nuclei, a certain fraction also have elevated rates of star formation in their disks with no significant star-formation activitiy being induced in their nuclei.