The complex kinematics of rotating star clusters in a tidal field

Tiongco, Maria; Vesperini, Enrico; Varri, Anna Lisa

doi:10.1093/mnrasl/sly009

Cited by 33 publications

(33 citation statements)

References 23 publications

(33 reference statements)

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“…However, in performing such an assessment, the size and radial distribution of the sample of stars under consideration can have a significant impact. Often, all of the stars are taken into account, but previous observational and theoretical studies have shown that position angle of the rotation axis can vary as a function of the radial distance from the cluster centre (see e.g., Gebhardt et al 2000, Bianchini et al 2013, Boberg et al 2017, Tiongco et al 2018. Thus, in the case of multiple populations co-existing in a star cluster, if the populations are not yet spatially mixed, each population may also have a different position angle of its rotation axis; this effect has already been partly noted in M13 by Cordero et al (2017).…”

Section: Discussionmentioning

confidence: 99%

“…The results of the long-term dynamical evolution of multiplepopulation clusters starting with a rotation axis in a generic orientation relative the cluster's orbital angular velocity vector show a number of complex kinematical features. As described in Tiongco et al (2018), the orientation of cluster's global rotation axis varies with time due to precession and nutation oscillations induced by the cluster's interaction with the host galaxy's tidal field. The rotation axis direction may also vary with radius within the cluster: the outer regions are more strongly affected by the external tidal field and their kinematical properties evolve to acquire a rotation around a direction closer to the direction of the cluster's orbital angular velocity vector.…”

Section: Discussionmentioning

confidence: 99%

“…Similar to Tiongco et al (2018), we present the analysis of our results using an inertial reference frame. In our analysis, we will refer to the global angular velocity vector, ω, calculated from an entire system of particles, and we define this vector to be the rotation axis of the system.…”

Section: Methods and Initial Conditionsmentioning

confidence: 99%

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Kinematical evolution of multiple stellar populations in star clusters

Tiongco

Vesperini

Varri

2019

Monthly Notices of the Royal Astronomical Society

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We present the results of a suite of N-body simulations aimed at understanding the fundamental aspects of the long-term evolution of the internal kinematics of multiple stellar populations in globular clusters. Our models enable us to study the cooperative effects of internal, relaxation-driven processes and external, tidally-induced perturbations on the structural and kinematic properties of multiple-population globular clusters. To analyse the dynamical behaviour of the multiple stellar populations in a variety of spin-orbit coupling conditions, we have considered three reference cases in which the tidally perturbed star cluster rotates along an axis oriented in different directions with respect to the orbital angular momentum vector. We focus specifically on the characterisation of the evolution of the degree of differential rotation and anisotropy in the velocity space, and we quantify the process of spatial and kinematic mixing of the two populations. In light of recent and forthcoming explorations of the internal kinematics of this class of stellar systems by means of line-of sight and astrometric measurements, we also investigate the implications of projection effects and spatial distribution of the stars adopted as tracers. The kinematic and structural richness emerging from our models further emphasises the need and the importance of observational studies aimed at building a complete kinematical picture of the multiple population phenomenon.1 Although we use the terms first-and second-generation to refer to the different populations, we point out that according to some formation models (see, e.g., Bastian et al. 2013, Gieles et al. 2018) all the populations form at the same time, and in those cases the two populations are more properly referred to as first-and second-population.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Kinematical evolution of multiple stellar populations in star clusters

Tiongco

Vesperini

Varri

2019

Monthly Notices of the Royal Astronomical Society

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“…In a forthcoming article, we will present a complete investigation based on a global, self-consistent, axisymmetric dynamical model, characterized by differential rotation and anisotropy in the velocity space (e.g., Varri & Bertin 2012), coupled with appropriate N-body simulations (e.g., Tiongco et al 2016Tiongco et al , 2017Tiongco et al , 2018. Nonetheless, here we present a first comparison between the radial profile of the ratio V rot /σ 0 and the time evolution of such a kinematic observable, as resulting from a representative N-body model from the survey recently conducted by Tiongco et al (2016Tiongco et al ( , 2018. Such a comparison, which is illustrated in Figure 13, supports the conclusion that M5 has already experienced the effects of two-body relaxation and angular momentum transport over the course of several initial half-mass relaxation times (t rh,i ).…”

Section: Discussionmentioning

confidence: 99%

The Strong Rotation of M5 (NGC 5904) as Seen from the MIKiS Survey of Galactic Globular Clusters

Lanzoni

Ferraro

Mucciarelli

et al. 2018

ApJ

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In the context of the ESO-VLT Multi-Instrument Kinematic Survey (MIKiS) of Galactic globular clusters (GGCs), we present the line-of-sight rotation curve and velocity dispersion profile of M5 (NGC 5904), as determined from the radial velocity of more than 800 individual stars observed out to 700″ (∼5 half-mass radii) from the center. We found one of the cleanest and most coherent rotation patterns ever observed for globular clusters, with a very stable rotation axis (having constant position angle of 145°at all surveyed radii) and a well-defined rotation curve. The density distribution turns out to be flattened in the direction perpendicular to the rotation axis, with a maximum ellipticity of ∼0.15. The rotation velocity peak (∼3 km s −1 in projection) is observed at ∼0.6 half-mass radii, and its ratio with respect to the central velocity dispersion (∼0.3-0.4 at 4 projected half-mass radii) indicates that ordered motions play a significant dynamical role. This result strengthens the growing empirical evidence of the kinematic complexity of GGCs and motivates the need of fundamental investigations of the role of angular momentum in collisional stellar dynamics.

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“…Where detailed measurements of kinematics are possible, rotation seems to be a common dynamical ingredient of NSCs (Feldmeier et al 2014;Nguyen et al 2018) and is also commonly found in a high fraction of GCs (van de Ven et al 2006;Bellazzini et al 2012;Bianchini et al 2013;Kacharov et al 2014;Fabricius et al 2014;Kimmig et al 2015;Bellini et al 2017;Kamann et al 2018;Bianchini et al 2018;Sollima et al 2019). The presence of internal rotation can be an indicator of their formation mechanism (Mastrobuono-Battisti & Perets 2013, 2016Hénault-Brunet et al 2015;Gavagnin et al 2016;Khoperskov et al 2018;Mastrobuono-Battisti et al 2019a) and can give important clues on their long-term dynamical evolution (e.g., Einsel & Spurzem 1999;Tiongco et al 2018). Fabricius et al (2014) and Kamann et al (2018) found that GCs with high internal central rotation are more flattened, showing that internal rotation plays an important role in forming the shape of GCs.…”

Section: Introductionmentioning

confidence: 99%

A Deep View into the Nucleus of the Sagittarius Dwarf Spheroidal Galaxy with MUSE. II. Kinematic Characterization of the Stellar Populations

Alfaro-Cuello

Kacharov

Neumayer

et al. 2020

ApJ

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The Sagittarius dwarf spheroidal galaxy (Sgr dSph) is in an advanced stage of disruption but still hosts its nuclear star cluster (NSC), M54, at its center. In this paper, we present a detailed kinematic characterization of the three stellar populations present in M54: young metal-rich (YMR); intermediate-age metal-rich (IMR); and old metal-poor (OMP), based on the spectra of ∼ 6500 individual M54 member stars extracted from a large MUSE/VLT dataset. We find that the OMP population is slightly flattened with a low amount of rotation (∼ 0.8 km s −1 ) and with a velocity dispersion that follows a Plummer profile. The YMR population displays a high amount of rotation (∼ 5 km s −1 ) and a high degree of flattening, with a lower and flat velocity dispersion profile. The IMR population shows a high but flat velocity dispersion profile, with some degree of rotation (∼ 2 km s −1 ). We complement our MUSE data with information from Gaia DR2 and confirm that the stars from the OMP and YMR populations are comoving in 3D space, suggesting that they are dynamically bound. While dynamical evolutionary effects (e.g. energy equipartition) are able to explain the differences in velocity dispersion between the stellar populations, the strong differences in rotation indicate different formation paths for the populations, as supported by an N-body simulation tailored to emulate the YMR-OMP system. This study provides additional evidence for the M54 formation scenario proposed in our previous work, where this NSC formed via GC accretion (OMP) and in situ formation from gas accretion in a rotationally supported disc (YMR).

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The complex kinematics of rotating star clusters in a tidal field

Cited by 33 publications

References 23 publications

Kinematical evolution of multiple stellar populations in star clusters

Kinematical evolution of multiple stellar populations in star clusters

The Strong Rotation of M5 (NGC 5904) as Seen from the MIKiS Survey of Galactic Globular Clusters

A Deep View into the Nucleus of the Sagittarius Dwarf Spheroidal Galaxy with MUSE. II. Kinematic Characterization of the Stellar Populations

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