Globular cluster formation with multiple stellar populations from hierarchical star cluster complexes

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Abstract

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.

Original languageEnglish
Pages (from-to)1857-1873
Number of pages17
JournalMonthly Notices of the Royal Astronomical Society
Volume467
Issue number2
DOIs
Publication statusPublished - May 2017

Cite this

@article{a309d65a674c47c78015b904da78edad,
title = "Globular cluster formation with multiple stellar populations from hierarchical star cluster complexes",
abstract = "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.",
keywords = "stars: formation, globular clusters: general, galaxies: ISM, galaxies: star clusters: general, galaxies: stellar content, LARGE-MAGELLANIC-CLOUD, DOUBLE MAIN-SEQUENCE, DWARF SPHEROIDAL GALAXY, OMEGA-CENTAURI, MILKY-WAY, NGC 1851, ABUNDANCE VARIATIONS, SPATIAL-DISTRIBUTION, DYNAMICAL EVOLUTION, FORMING GALAXIES",
author = "Kenji Bekki",
year = "2017",
month = "5",
doi = "10.1093/mnras/stx110",
language = "English",
volume = "467",
pages = "1857--1873",
journal = "Monthly Notices of the Royal Astronomical Society",
issn = "0035-8711",
publisher = "OXFORD UNIV PRESS UNITED KINGDOM",
number = "2",

}

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

VL - 467

SP - 1857

EP - 1873

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 0035-8711

IS - 2

ER -