The early evolution of star clusters in compressive and extensive tidal fields

Webb, Jeremy J.; Patel, Saahil; Vesperini, Enrico

doi:10.1093/mnrasl/slx030

Cited by 9 publications

(4 citation statements)

References 40 publications

(39 reference statements)

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“…In the accretion scenario, a cluster initially orbit deep in the potential well of a dwarf and is not stripped until its previous host reaches the inner parts of the Milky Way ans is near dissolution. In this latter scenario the cluster still orbits in a strong tidal field for the majority of its life, but while a member of a dwarf galaxy the tidal field may be compressive (Bianchini et al 2015;Webb et al 2017b).…”

Section: Analysis and Discussionmentioning

confidence: 99%

Characteristic radii of the Milky Way globular clusters

Piatti

Webb

Carlberg

2019

Monthly Notices of the Royal Astronomical Society

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We report on the extent of the effects of the Milky Way's gravitational field in shaping the structural parameters and internal dynamics of its globular cluster population. We make use of a homogeneous, up-to-date data set with kinematics, structural properties, current and initial masses of 156 globular clusters. In general, cluster radii increase as the Milky Way potential weakens; with the core and Jacobi radii being those which increase at the slowest and fastest rate respectively. We interpret this result as the innermost regions of globular clusters being less sensitive to changes in the tidal forces with the Galactocentric distance. The Milky Way's gravitational field also seems to have differentially accelerated the internal dynamical evolution of individual clusters, with those toward the bulge appearing dynamically older. Finally we find a sub-population consisting of both compact and extended globular clusters (as defined by their r h /r J ratio) beyond 8 kpc that appear to have lost a large fraction of their initial mass lost via disruption. Moreover, we identify a third group with r h /r J > 0.4, which have lost an even larger fraction of their initial mass by disruption. In both cases the high fraction of mass lost is likely due to their large orbital eccentricities and inclination angles, which lead to them experiencing more tidal shocks at perigalacticon and during disc crossings. Comparing the structural and orbital parameters of individual clusters allows for constraints to be placed on whether or not their evolution was relaxation or tidally dominated.

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Section: Analysis and Discussionmentioning

confidence: 99%

Characteristic radii of the Milky Way globular clusters

Piatti

Webb

Carlberg

2019

Monthly Notices of the Royal Astronomical Society

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“…In this case, both pure extensive and compressive tides will contribute to the disruption process (Webb et al 2017), therefore λ m serves as an upper limit of the tidal strength. Alternatively, we discuss below also a case with…”

Section: Disruption Time-scales and The Bound Fractionmentioning

confidence: 99%

Star cluster formation in cosmological simulations – III. Dynamical and chemical evolution

Gnedin

2019

Monthly Notices of the Royal Astronomical Society

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In previous papers of this series, we developed a new algorithm for modelling the formation of star clusters in galaxy formation simulations. Here we investigate how dissolution of bound star clusters affects the shape of the cluster mass function and the metallicity distribution of surviving clusters. Cluster evolution includes the loss of stars that become unbound due to tidal disruption as well as mass-loss due to stellar evolution. We calculate the tidal tensor along cluster trajectories and use it to estimate the instantaneous mass-loss rate. The typical tidal tensor exhibits large variations on a time-scale of ∼ 100 Myr, with maximum eigenvalue of 10 7 Gyr −2 , and median value of 10 4 Gyr −2 for the first Gyr after cluster formation. As a result of dynamical disruption, at the final available output of our simulations at redshift z ≈ 1.5, the cluster mass function has an approximately log-normal shape peaked at ∼ 10 4.3 M . Extrapolation of the disruption to z = 0 results in too many low-mass clusters compared to the observed Galactic globular clusters (GCs). Over 70% of GC candidates are completely disrupted before the present; only 10% of the total GC candidate mass remains in surviving clusters. The total mass of surviving clusters at z = 0 varies from run to run in the range (2 − 6) × 10 7 M , consistent with the observed mass of GC systems in Milky Way-sized galaxies. The metallicity distributions of all massive star clusters and of the surviving GCs have similar shapes but different normalization because of cluster disruption. The model produces a larger fraction of very metal-poor clusters than observed. A robust prediction of the model is the age-metallicity relation, in which metal-rich clusters are systematically younger than metal-poor clusters by up to 3 Gyr.

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“…The cluster in the cored galaxy also expands, but > ∼ 5 Gyr the star cluster evolves at roughly constant M cl and constant r hm . This is because the escape rate is very small in compressive tides, and the cluster evolves towards a near isothermal equilibrium configuration, in which the cluster is in virial equilibrium with the tides (Yoon, Lee, & Hong 2011;Bianchini et al 2015;Webb, Patel, & Vesperini 2017). This implies that it is more likely to find a cluster in this phase, because it can be in this quasi-equilibrium configuration for a long time ( 10 Gyr).…”

Section: Best-fit Star Cluster Modelsmentioning

confidence: 99%

Probing dark matter with star clusters: a dark matter core in the ultra-faint dwarf Eridanus II

Contenta

Balbinot

Petts

et al. 2018

Monthly Notices of the Royal Astronomical Society

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We present a new technique to probe the central dark matter (DM) density profile of galaxies that harnesses both the survival and observed properties of star clusters. As a first application, we apply our method to the 'ultra-faint' dwarf Eridanus II (Eri II) that has a lone star cluster ∼ 45 pc from its centre. Using a grid of collisional N-body simulations, incorporating the effects of stellar evolution, external tides and dynamical friction, we show that a DM core for Eri II naturally reproduces the size and the projected position of its star cluster. By contrast, a dense cusped galaxy requires the cluster to lie implausibly far from the centre of Eri II (> 1 kpc), with a high inclination orbit that must be observed at a particular orbital phase. Our results, therefore, favour a dark matter core. This implies that either a cold DM cusp was 'heated up' at the centre of Eri II by bursty star formation, or we are seeing an evidence for physics beyond cold DM.

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The early evolution of star clusters in compressive and extensive tidal fields

Cited by 9 publications

References 40 publications

Characteristic radii of the Milky Way globular clusters

Characteristic radii of the Milky Way globular clusters

Star cluster formation in cosmological simulations – III. Dynamical and chemical evolution

Probing dark matter with star clusters: a dark matter core in the ultra-faint dwarf Eridanus II

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