The effect of primordial mass segregation on the size scale of globular clusters

Haghi, Hosein; Hoseini-Rad, Seyed Mohammad; Zonoozi, Akram Hasani; Küpper, Andreas H. W.

doi:10.1093/mnras/stu1714

Cited by 19 publications

(22 citation statements)

References 79 publications

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“…For this reason, these stellar systems could have genuinely formed extended or could have experienced an enhanced expansion due to some internal dynamical mechanism (e.g. the interplay of primordial mass segregation and dynamical relaxation, Haghi et al 2014). Alternatively, observations of the radius of extended clusters could be biased by unbound stars that have already been stripped, and wonder in its vicinity along its orbit (Küpper et al 2010).…”

Section: Discussionmentioning

confidence: 99%

“…The current relaxation time of this extended cluster exceeds the Hubble time and therefore is too long to explain the settling of segregation only through dynamical evolution. The combined effect of primordial mass segregation and dynamical evolution could explain the structure of this cluster (Haghi et al 2014). Therefore, further studies of the internal properties of such stellar systems are indeed crucial to unveil their origin.…”

Section: Introductionmentioning

confidence: 95%

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The inefficiency of satellite accretion in forming extended star clusters

Bianchini

Renaud

Gieles

et al. 2014

Monthly Notices of the Royal Astronomical Society: Letters

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The distinction between globular clusters and dwarf galaxies has been progressively blurred by the recent discoveries of several extended star clusters, with size (20 − 30 pc) and luminosity (−6 < M v < −2) comparable to the one of faint dwarf spheroidals. In order to explain their sparse structure, it has been suggested that they formed as star clusters in dwarf galaxy satellites that later accreted onto the Milky Way. If these clusters form in the centre of dwarf galaxies, they evolve in a tidally-compressive environment where the contribution of the tides to the virial balance can become significant, and lead to a super-virial state and subsequent expansion of the cluster, once removed. Using N -body simulations, we show that a cluster formed in such an extreme environment undergoes a sizable expansion, during the drastic variation of the external tidal field due to the accretion process. However, we show that the expansion due to the removal of the compressive tides is not enough to explain the observed extended structure, since the stellar systems resulting from this process are always more compact than the corresponding clusters that expand in isolation due to twobody relaxation. We conclude that an accreted origin of extended globular clusters is unlikely to explain their large spatial extent, and rather favor the hypothesis that such clusters are already extended at the stage of their formation.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 95%

The inefficiency of satellite accretion in forming extended star clusters

Bianchini

Renaud

Gieles

et al. 2014

Monthly Notices of the Royal Astronomical Society: Letters

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“…Even in the case of mass-loss driven by stellar evolutionary expansion, the amount of mass lost is expected to be inversely proportional to GC mass and Galactocentric radius, although it may be somewhat different in magnitude relative to two-body relaxation driven tidal stripping. The effects of primordial mass segregation, and its role in cluster dissolution through stellar evolutionary induced cluster expansion, has been studied numerically by Haghi et al (2014). The authors carried out a suite of N-body simulations of clusters in a Milky Way type potential, for clusters with and without mass segregation.…”

Section: Evolution Of Clusters In a Tidal Fieldmentioning

confidence: 99%

Globular cluster mass-loss in the context of multiple populations: Figure 1.

Bastian

Lardo

2015

Mon. Not. R. Astron. Soc.

100

104

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Many scenarios for the origin of the chemical anomalies observed in globular clusters (GCs; i.e., multiple populations) require that GCs were much more massive at birth, up to 10 − 100×, than they are presently. This is invoked in order to have enough material processed through first generation stars in order to form the observed numbers of enriched stars (inferred to be second generation stars in these models). If such mass loss was due to tidal stripping, gas expulsion, or tidal interaction with the birth environment, there should be clear correlations between the fraction of enriched stars and other cluster properties, whereas the observations show a remarkably uniform enriched fraction of 0.68 ± 0.07 (from 33 observed GCs). If interpreted in the heavy mass loss paradigm, this means that all GCs lost the same fraction of their initial mass (between 95 − 98%), regardless of their mass, metallicity, location at birth or subsequent migration, or epoch of formation. This is incompatible with predictions, hence we suggest that GCs were not significantly more massive at birth, and that the fraction of enriched to primordial stars observed in clusters today likely reflects their initial value. If true, this would rule out self-enrichment through nucleosynthesis as a viable solution to the multiple population phenomenon.

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“…Finally, primordial mass segregation can strengthen the early expansion due to stellar evolution and further enhance the early rate of star escape (see e.g. Vesperini et al 2009, Haghi et al 2014.…”

Section: Evolution Of the Fraction Of Second-generation Starsmentioning

confidence: 99%

Dynamical evolution and spatial mixing of multiple population globular clusters

Vesperini

McMillan

D’Antona

et al. 2013

Monthly Notices of the Royal Astronomical Society

160

176

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Numerous spectroscopic and photometric observational studies have provided strong evidence for the widespread presence of multiple stellar populations in globular clusters. In this paper we study the long-term dynamical evolution of multiple-population clusters, focusing on the evolution of the spatial distributions of the first-(FG) and second-generation (SG) stars. In previous studies we have suggested that SG stars formed from the ejecta of FG AGB stars are expected initially to be concentrated in the cluster inner regions. Here, by means of N -body simulations, we explore the time scales and the dynamics of the spatial mixing of the FG and the SG populations and their dependence on the SG initial concentration.Our simulations show that, as the evolution proceeds, the radial profile of the SG/FG number ratio, N SG /N F G , is characterized by three regions: 1) a flat inner part; 2) a declining part in which FG stars are increasingly dominant; and 3) an outer region where the N SG /N F G profile flattens again (the N SG /N F G profile may rise slightly again in the outermost cluster regions). Until mixing is complete and the N SG /N F G profile is flat over the entire cluster, the radial variation of N SG /N F G implies that the fraction of SG stars determined by observations covering a limited range of radial distances is not, in general, equal to the SG global fraction, (N SG /N F G ) glob . The distance at which N SG /N F G equals (N SG /N F G ) glob is approximately between 1 and 2 cluster half-mass radii. The time scale for complete mixing depends on the SG initial concentration, but in all cases complete mixing is expected only for clusters in advanced evolutionary phases, having lost at least 60-70 percent of their mass due to two-body relaxation (in addition to the early FG loss due to the cluster expansion triggered by SNII ejecta and gas expulsion).The results of our simulations suggest that in many Galactic globular clusters the SG should still be more spatially concentrated than the FG.

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The effect of primordial mass segregation on the size scale of globular clusters

Cited by 19 publications

References 79 publications

The inefficiency of satellite accretion in forming extended star clusters

The inefficiency of satellite accretion in forming extended star clusters

Globular cluster mass-loss in the context of multiple populations: Figure 1.

Dynamical evolution and spatial mixing of multiple population globular clusters

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