Formation of globular clusters with multiple stellar populations from massive gas clumps in high-z gas-rich dwarf galaxies

Abstract

One of the currently favored scenarios for the formation of globular clusters (GCs) with multiple stellar populations is that an initial massive stellar system forms (`first generation', FG), subsequently giving rise to gaseous ejecta which is converted into a second generation (SG) of stars to form a GC. We investigate, for the first time, the sequential formation processes of both FG and SG stars from star-forming massive gas clumps in gas-rich dwarf disk galaxies. We adopt a novel approach to resolve the two-stage formation of GCs in hydrodynamical simulations of dwarf galaxies.In the new simulations, new gas particles that are much less massive than their parent star particle are generated around each new star particle when the new star enters into the asymptotic giant branch (AGB) phase. Furthermore, much finer maximum time step width (<10^5 yr) and smaller softening length (<2 pc) are adopted for such AGB gas particles to properly resolve the ejection of gas from AGB stars and AGB feedback effects. Therefore, secondary star formation from AGB ejecta can be properly investigated in galaxy-scale simulations. An FG stellar system can first form from a massive gas clump developing due to gravitational instability within its host gas-rich dwarf galaxy. Initially the FG stellar system is not a single massive cluster, but instead is composed of several irregular stellar clumps (or filaments) with a total mass larger than 10^6 Msun. While the FG system is dynamically relaxing, gaseous ejecta from AGB stars can be gravitationally trapped by the FG system and subsequently converted into new stars to form a compact SG stellar system within the FG system. Interestingly, about 40% of AGB ejecta is from stars that do not belong to the FG system (`external gas accretion'). The mass-density relation for SG stellar systems can be approximated as rho_SG ~ M_SG^1.5.