Formation of Galactic Disk Globular Clusters in Early Dissipative Minor Merging

Abstract

The origin of metal-rich, highly flattened, and rapidly rotating disk globular cluster systems in the Galaxy is one of long-standing issues in the context of the Galaxy formation. Our numerical simulations suggest a new, twofold scenario in which the disk globular clusters are first formed in the high-pressure, dense central region of a gas-rich dwarf galaxy, as induced during the tidal interaction with the pre-existing, young, thin disk of the Galaxy, and then dispersed into the disk region owing to the final tidal destruction of the merging dwarf. We also demonstrate that spatial distribution, total number, and metallicity distribution of the clusters formed in this minor merging depend on the mass ratio of the host to dwarf galaxy and the orbital configuration of merging. Based on these results, we discuss whether a minor merging event about 10 Gyr ago can explain both the Galactic thick disk and disk globular clusters. Several other implications for the possible relation between the properties of disk galaxies and their disk globular clusters are also discussed.