The properties of energetically unbound stars in stellar clusters

Claydon, Ian; Gieles, M.; Zocchi, Alice

doi:10.1093/mnras/stw3309

Cited by 50 publications

(66 citation statements)

References 75 publications

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“…Our analysis reveals flattened velocity dispersion profiles starting from the tidal radius (≈ 40 pc) until beyond the Jacobi radius, settling around values of ∼ 2.5−4 km s −1 , with an average velocity dispersion along the two components of 3.5 ± 0.9 km s −1 at the Jacobi radius. This is in tension with what expected from the presence of potential escapers stars (Claydon et al 2017) at a ∼3-sigma confidence level. However, note that we cannot exclude that small-scale systematics in the Gaia DR2 catalog could still produce an inflation of the velocity dispersion profiles of the order of < 1 km s −1 .…”

Section: Resultscontrasting

confidence: 61%

“…Fukushige & Heggie 2000;Küpper et al 2010;Daniel et al 2017). The number of potential escapers is comparable to the number of bound stars around 0.5 r j and dominates at larger radii (Claydon et al 2017). As a result, they produce a flattening of the velocity dispersion profile.…”

Section: Flattening Of the Velocity Dispersion Profilesmentioning

confidence: 93%

“…Observation radial radial tangential tangential measurement at the Jacobi radius 3.5 ± 0.9 km s −1 is ∼ 3-sigma discrepant from the theoretical expectation. This discrepancy can be taken as evidence of a peculiar dynamical history of NGC3201 or of some drawbacks due to the simplified framework adopted by Claydon et al (2017) for the potential escapers calculation, which include many uncertain ingredients, such as the initial condition of the GC, its orbit and the Galactic potential. For example, if the cluster formed in a dwarf galaxy that later accreted onto the MW, it could have experienced a different tidal field than the one inferred by the current orbital properties.…”

Section: Simulationmentioning

confidence: 99%

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Exploring the Outskirts of Globular Clusters: The Peculiar Kinematics of NGC 3201

Bianchini

Ibata

Famaey

2019

ApJL

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The outskirts of globular clusters (GCs) simultaneously retain crucial information about their formation mechanism and the properties of their host galaxy. Thanks to the advent of precision astrometry both their morphological and kinematic properties are now accessible. Here we present the first dynamical study of the outskirts of the retrograde GC NGC3201 until twice its Jacobi radius (< 100 pc), using specifically-selected high-quality astrometric data from Gaia DR2. We report the discovery of a stellar overdensity along the South-East/North-West direction that we identify as tidal tails. The GC is characterized globally by radial anisotropy and a hint of isotropy in the outer parts, with an excess of tangential orbits around the lobes corresponding to the tidal tails, in qualitative agreement with an N -body simulation. Moreover, we measure flat velocity dispersion profiles, reaching values of 3.5 ± 0.9 km s −1 until beyond the Jacobi radius. While tidal tails could contribute to such a flattening, this high velocity dispersion value is in disagreement with the expectation from the sole presence of potential escapers. To explain this puzzling observation, we discuss the possibility of an accreted origin of the GC, the presence of a dark matter halo -leftover of its formation at high redshift -and the possible effects of non-Newtonian dynamics. Our study uncovers a new path for the study of GC formation and of the properties of the Milky Way potential in the era of precision astrometry.

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Section: Resultscontrasting

confidence: 61%

Section: Flattening Of the Velocity Dispersion Profilesmentioning

confidence: 93%

Section: Simulationmentioning

confidence: 99%

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Exploring the Outskirts of Globular Clusters: The Peculiar Kinematics of NGC 3201

Bianchini

Ibata

Famaey

2019

ApJL

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“…In the outer parts of globular clusters, where a larger fraction of stars are nonmembers, the approach used by Scarpa et al is likely to overestimate the velocity dispersion. The agreement with our models could probably be improved further since the simulations presented here do not include tidal fields, which increase the velocity dispersion of stars near the tidal radius (Küpper et al 2010;Claydon, Gieles & Zocchi 2015).…”

Section: Intermediate-mass Black Holessupporting

confidence: 57%

N-body modelling of globular clusters: masses, mass-to-light ratios and intermediate-mass black holes

Baumgardt

2016

Mon. Not. R. Astron. Soc.

206

252

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We have determined the masses and mass-to-light ratios of 50 Galactic globular clusters by comparing their velocity dispersion and surface brightness profiles against a large grid of 900 N -body simulations of star clusters of varying initial concentration, size and central black hole mass fraction. Our models follow the evolution of the clusters under the combined effects of stellar evolution and two-body relaxation allowing us to take the effects of mass segregation and energy equipartition between stars selfconsistently into account. For a subset of 16 well observed clusters we also derive their kinematic distances. We find an average mass-to-light ratio of Galactic globular clusters of < M/L V >= 1.98 ± 0.03, which agrees very well with the expected M/L ratio if the initial mass function (IMF) of the clusters was a standard Kroupa or Chabrier mass function. We do not find evidence for a decrease of the average mass-to-light ratio with metallicity. The surface brightness and velocity dispersion profiles of most globular clusters are incompatible with the presence of intermediate-mass black holes (IMBHs) with more than a few thousand M ⊙ in them. The only clear exception is ω Cen, where the velocity dispersion profile provides strong evidence for the presence of a ∼40,000 M ⊙ IMBH in the centre of the cluster.

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“…We simulated the orbits of the globular clusters using the spray-particle implementation by Küpper et al (2012), where the escape velocity was modified to match that observed in N-body simulations with realistic tidal fields (Claydon et al 2017). We assume a Milky Way potential similar to the best-fit Palomar 5 model , but with a Jaffe bulge.…”

Section: Globular Clustersmentioning

confidence: 99%

Stellar Streams Discovered in the Dark Energy Survey

Shipp

Drlica-Wagner

Balbinot

et al. 2018

ApJ

246

254

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We perform a search for stellar streams around the Milky Way using the first 3 yr of multiband optical imaging data from the Dark Energy Survey (DES). We use DES data covering ∼5000 deg 2 to a depth of g>23.5 with a relative photometric calibration uncertainty of <1%. This data set yields unprecedented sensitivity to the stellar density field in the southern celestial hemisphere, enabling the detection of faint stellar streams to a heliocentric distance of ∼50 kpc. We search for stellar streams using a matched filter in color-magnitude space derived from a synthetic isochrone of an old, metal-poor stellar population. Our detection technique recovers four previously known thin stellar streams: Phoenix, ATLAS, Tucana III, and a possible extension of Molonglo. In addition, we report the discovery of 11 new stellar streams. In general, the new streams detected by DES are fainter, more distant, and lower surface brightness than streams detected by similar techniques in previous photometric surveys. As a by-product of our stellar stream search, we find evidence for extratidal stellar structure associated with four globular clusters: NGC 288, NGC 1261, NGC 1851, and NGC 1904. The ever-growing sample of stellar streams will provide insight into the formation of the Galactic stellar halo, the Milky Way gravitational potential, and the large-and small-scale distribution of dark matter around the Milky Way.

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The properties of energetically unbound stars in stellar clusters

Cited by 50 publications

References 75 publications

Exploring the Outskirts of Globular Clusters: The Peculiar Kinematics of NGC 3201

Exploring the Outskirts of Globular Clusters: The Peculiar Kinematics of NGC 3201

N-body modelling of globular clusters: masses, mass-to-light ratios and intermediate-mass black holes

Stellar Streams Discovered in the Dark Energy Survey

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