Dynamical constraints on the origin of multiple stellar populations in globular clusters

Khalaj, Pouria; Baumgardt, Holger

doi:10.1093/mnras/stv1356

Cited by 38 publications

(45 citation statements)

References 81 publications

(127 reference statements)

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“…A similar conclusion was reach with different arguments by Khalaj & Baumgardt (2015) and Bastian & Lardo (2015).…”

Section: Model Grid: Importance Of Compactness and Star Formation Effsupporting

confidence: 85%

“…remove 95 per cent of the stars, gas expulsion needs to be explosive (Decressin et al 2010;Khalaj & Baumgardt 2015), i.e. happen on the crossing timescale of the cluster.…”

Section: Light-element Anti-correlations In Globular Clustersmentioning

confidence: 99%

“…If gas expulsion would work in multiple population clusters, one would expect a correlation between the total stellar mass and the fraction of enriched stars, which is, however, not seen (Khalaj & Baumgardt 2015;Bastian & Lardo 2015).…”

Section: Light-element Anti-correlations In Globular Clustersmentioning

confidence: 99%

“…Gas expulsion and multiple populations 5.3.1. Constraints from N-body simulations Khalaj & Baumgardt (2015) show N-body simulations of star clusters that contain chemically normal (first generation) and peculiar (second generation) stars. With a simple model of gas expulsion they find that star formation efficiencies 50 per cent are needed in order to produce star clusters with final ratios of first to second generation stars close to the ones observed in presentday globular clusters in the Milky Way.…”

Section: Model Grid: Importance Of Compactness and Star Formation Effmentioning

confidence: 99%

“…However, their masses must have been even higher, and the radii smaller, if gas expulsion would indeed have been at work in these objects: Bastian & Lardo (2015) compare the first to second generation ratios predicted by Khalaj & Baumgardt (2015) to observations and find that all clusters that show the Na-O anti-correlation should have lost a very similar fraction of stars, between 95 and 98 per cent of the initial number (compare also Prantzos & Charbonnel 2006;Carretta et al 2010;D'Ercole et al 2010). Expansion factors are up to a few (Khalaj & Baumgardt 2015). The current C 5 -values, 0.05-3.2, would hence transform to the range of about 1 to 100 for the initial compactness indices.…”

Section: Model Grid: Importance Of Compactness and Star Formation Effmentioning

confidence: 99%

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Gas expulsion in massive star clusters?

Krause

Charbonnel

Bastian

et al. 2016

A&A

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Context. Gas expulsion is a central concept in some of the models for multiple populations and the light-element anti-correlations in globular clusters. If the star formation efficiency was around 30 per cent and the gas expulsion happened on the crossing timescale, this process could preferentially expel stars born with the chemical composition of the proto-cluster gas, while stars with special composition born in the centre would remain bound. Recently, a sample of extragalactic, gas-free, young massive clusters has been identified that has the potential to test the conditions for gas expulsion. Aims. We investigate the conditions required for residual gas expulsion on the crossing timescale. We consider a standard initial mass function and different models for the energy production in the cluster: metallicity-dependent stellar winds, radiation, supernovae and more energetic events, such as hypernovae, which are related to gamma ray bursts. The latter may be more energetic than supernovae by up to two orders of magnitude. Methods. We computed a large number of thin-shell models for the gas dynamics, and calculated whether the Rayleigh-Taylor instability is able to disrupt the shell before it reaches the escape speed. Results. We show that the success of gas expulsion depends on the compactness index of a star cluster C 5 ≡ (M * /10 5 M )/(r h /pc), with initial stellar mass M * and half-mass radius r h . For given C 5 , a certain critical, local star formation efficiency is required to remove the rest of the gas. Common stellar feedback processes may not lead to gas expulsion with significant loss of stars above C 5 ≈ 1. Considering pulsar winds and hypernovae, the limit increases to C 5 ≈ 30. If successful, gas expulsion generally takes place on the crossing timescale. Some observed young massive clusters have 1 < C 5 < 10 and are gas-free at ≈10 Myr. This suggests that gas expulsion does not affect their stellar mass significantly, unless powerful pulsar winds and hypernovae are common in such objects. By comparison to observations, we show that C 5 is a better predictor for the expression of multiple populations than stellar mass. The best separation between star clusters with and without multiple populations is achieved by a stellar winds-based gas expulsion model, where gas expulsion would occur exclusively in star clusters without multiple populations. Single and multiple population clusters also have little overlap in metallicity and age. Conclusions. Globular clusters should initially have C 5 100, if the gas expulsion paradigm was correct. Early gas expulsion, which is suggested by the young massive cluster observations, hence would require special circumstances, and is excluded for several objects. Most likely, the stellar masses did not change significantly at the removal of the primordial gas. Instead, the predictive power of the C 5 index for the expression of multiple populations is consistent with the idea that gas expulsion may prevent the expression of multiple populations. On this bas...

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“…A similar conclusion was reach with different arguments by Khalaj & Baumgardt (2015) and Bastian & Lardo (2015).…”

Section: Model Grid: Importance Of Compactness and Star Formation Effsupporting

confidence: 85%

“…remove 95 per cent of the stars, gas expulsion needs to be explosive (Decressin et al 2010;Khalaj & Baumgardt 2015), i.e. happen on the crossing timescale of the cluster.…”

Section: Light-element Anti-correlations In Globular Clustersmentioning

confidence: 99%

Section: Light-element Anti-correlations In Globular Clustersmentioning

confidence: 99%

Section: Model Grid: Importance Of Compactness and Star Formation Effmentioning

confidence: 99%

Section: Model Grid: Importance Of Compactness and Star Formation Effmentioning

confidence: 99%

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Gas expulsion in massive star clusters?

Krause

Charbonnel

Bastian

et al. 2016

A&A

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Globular clusters and their contribution to the formation of the Galactic halo

Carretta

2015

Proc. IAU

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This is a "biased" review because I will show recent evidence on the contribution of globular clusters (GCs) to the halo of our Galaxy seen through the lens of the new paradigm of multiple populations in GCs. I will show a few examples where the chemistry of multiple populations helps to answer hot questions including whether and how much GCs did contribute to the halo population, if we have evidence of the GCs-halo link, what are the strengths and weak points concerning this contribution.

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A critical assessment of models for the origin of multiple populations in globular clusters

Bastian

2015

Proc. IAU

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A number of scenarios have been put forward to explain the origin of the chemical anomalies (and resulting complex colour-magnitude diagrams) observed in globular clusters (GCs), namely the AGB, Fast Rotating Massive Star, Very Massive Star, and Early Disc Accretion scenarios. We compare the predictions of these scenarios with a range of observations (including young massive clusters (YMCs), chemical patterns, and GC population properties) and find that all models are inconsistent with observations. In particular, YMCs do not show evidence for multiple epochs of star-formation and appear to be gas free by an age of ~ 3 Myr. Also, the chemical patterns displayed in GCs vary from one to the next in such a way that cannot be reproduced by standard nucleosynthetic yields. Finally, we show that the “mass budget problem” for the scenarios cannot be solved by invoking heavy cluster mass loss (i.e. that clusters were 10-100 times more massive at birth) as this solution makes basic predictions about the GC population that are inconsistent with observations. We conclude that none of the proposed scenarios can explain the multiple population phenomenon, hence alternative theories are needed.

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Dynamical constraints on the origin of multiple stellar populations in globular clusters

Cited by 38 publications

References 81 publications

Gas expulsion in massive star clusters?

Gas expulsion in massive star clusters?

Globular clusters and their contribution to the formation of the Galactic halo

A critical assessment of models for the origin of multiple populations in globular clusters

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