Star formation history in merging galaxies

Galaxy mergers are believed to have an important role in many aspects of galactic evolution. Violent interactions between galaxies are also believed to be the trigger of starbursts. Some of the young massive and compact star clusters born in the starbursts are likely to become young globular clusters, once they survived early disruption processes. The ages of these young clusters can thus be interpreted to yield the timing of interaction-triggered events, and provide crucial information to reconstruct the star formation history of the galaxy mergers. On a larger scale, the triggers of star formation in interacting galaxies are still not well understood. Studies suggest a simple relation between star formation rate and gas density; alternatively large-scale shocks have also been suggested as another trigger of star formation. The main objective of this dissertation is to combine predictions from numerical models with observations of young star clusters formed during the process of merger in order to determine the trigger of star formation in merging galaxies. We searched for such young clusters in six merging galaxies at different merger stages---Arp 256, NGC 7469, NGC 4676, Arp 299, IC 883, and NGC 2623. We found that, although the evolution of these clusters in the next several hundreds of Myr is still unknown, their age distributions seem to show a trend of merger stages: the distribution of ages becomes broader as the merger stage advances. Our study of the metallicities of these clusters shows that the distribution of these metallicities seems to agree with the prediction from scenarios of gas inflow in mergers. We also present dynamical and star-forming models of Arp 256 and NGC 7252. The shock-induced model of these two galaxy mergers both predict a prompt star formation enhancement at the first passage, while the strength depends on the encounter geometry, and a wider distribution of induced star formation throughout the merger than the density-dependent model. The results from comparisons of observation and simulation of the three galaxy mergers, Arp 256, NGC 4676, and NGC 7252, show that the overall age distributions and locations of the clusters observed in these systems are more consistent with the shock-induced models. We conclude that the importance of the shock-induced star formation mechanism in triggering star formation in galaxy mergers should be emphasized.