TY - JOUR
T1 - Globular cluster formation with multiple stellar populations from hierarchical star cluster complexes
AU - Bekki, Kenji
PY - 2017/5
Y1 - 2017/5
N2 - Most old globular clusters (GCs) in the Galaxy are observed to have internal chemical abundance spreads in light elements. We discuss a new GC formation scenario based on hierarchical star formation within fractal molecular clouds. In the new scenario, a cluster of bound and unbound star clusters ('star cluster complex', SCC) that have a power-law cluster mass function with a slope (beta) of 2 is first formed from a massive gas clump developed in a dwarf galaxy. Such cluster complexes and beta = 2 are observed and expected from hierarchical star formation. The most massive star cluster ('main cluster'), which is the progenitor of a GC, can accrete gas ejected from asymptotic giant branch (AGB) stars initially in the cluster and other low-mass clusters before the clusters are tidally stripped or destroyed to become field stars in the dwarf. The SCC is initially embedded in a giant gas hole created by numerous supernovae of the SCC so that cold gas outside the hole can be accreted on to the main cluster later. New stars formed from the accreted gas have chemical abundances that are different from those of the original SCC. Using hydrodynamical simulations of GC formation based on this scenario, we show that the main cluster with the initial mass as large as [2-5] x 10(5) M-circle dot can accrete more than 10(5) M-circle dot gas from AGB stars of the SCC. We suggest that merging of hierarchical SSCs can play key roles in stellar halo formation around GCs and self-enrichment processes in the early phase of GC formation.
AB - Most old globular clusters (GCs) in the Galaxy are observed to have internal chemical abundance spreads in light elements. We discuss a new GC formation scenario based on hierarchical star formation within fractal molecular clouds. In the new scenario, a cluster of bound and unbound star clusters ('star cluster complex', SCC) that have a power-law cluster mass function with a slope (beta) of 2 is first formed from a massive gas clump developed in a dwarf galaxy. Such cluster complexes and beta = 2 are observed and expected from hierarchical star formation. The most massive star cluster ('main cluster'), which is the progenitor of a GC, can accrete gas ejected from asymptotic giant branch (AGB) stars initially in the cluster and other low-mass clusters before the clusters are tidally stripped or destroyed to become field stars in the dwarf. The SCC is initially embedded in a giant gas hole created by numerous supernovae of the SCC so that cold gas outside the hole can be accreted on to the main cluster later. New stars formed from the accreted gas have chemical abundances that are different from those of the original SCC. Using hydrodynamical simulations of GC formation based on this scenario, we show that the main cluster with the initial mass as large as [2-5] x 10(5) M-circle dot can accrete more than 10(5) M-circle dot gas from AGB stars of the SCC. We suggest that merging of hierarchical SSCs can play key roles in stellar halo formation around GCs and self-enrichment processes in the early phase of GC formation.
KW - stars: formation
KW - globular clusters: general
KW - galaxies: ISM
KW - galaxies: star clusters: general
KW - galaxies: stellar content
KW - LARGE-MAGELLANIC-CLOUD
KW - DOUBLE MAIN-SEQUENCE
KW - DWARF SPHEROIDAL GALAXY
KW - OMEGA-CENTAURI
KW - MILKY-WAY
KW - NGC 1851
KW - ABUNDANCE VARIATIONS
KW - SPATIAL-DISTRIBUTION
KW - DYNAMICAL EVOLUTION
KW - FORMING GALAXIES
U2 - 10.1093/mnras/stx110
DO - 10.1093/mnras/stx110
M3 - Article
SN - 0035-8711
VL - 467
SP - 1857
EP - 1873
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 2
ER -