<i>N</i>-body models of globular clusters: metallicities, half-light radii and mass-to-light ratios

Sippel, Anna C.; Hurley, Jarrod R.; Madrid, Juan P.; Harris, William E.

doi:10.1111/j.1365-2966.2012.21969.x

Cited by 40 publications

(12 citation statements)

References 77 publications

(146 reference statements)

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“…Moreover, at a fixed age of 11 Gyr, metal rich clusters have on average higher M/L, because of a decrease in luminosity due to higher stellar opacity (e.g. Sippel et al 2012), as expected from stellar population models. In panel C and D of Fig.…”

Section: Global Relationsmentioning

confidence: 86%

“…A signature of a dependence of the relaxation time on the metallicity of the clusters is present in the data of Strader et al (2011), where GCs with higher metallicity show a lower relaxation time, on average. However, we should be cautious about this trend due to possible observational effects biasing the measurements of the half-light radii (and therefore of the relaxation times) of metal rich clusters (i.e., the combined effect of stellar evolution and mass segregation can bias the cluster size measurements, giving lower values for the halflight radii for metal rich clusters; see for example Sippel et al 2012;Shanahan & Gieles 2015).…”

Section: Discussionmentioning

confidence: 99%

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The relation between the mass-to-light ratio and the relaxation state of globular clusters

Bianchini

Sills

Ven

et al. 2017

Monthly Notices of the Royal Astronomical Society

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The internal dynamics of globular clusters (GCs) is strongly affected by two-body interactions that bring the systems to a state of partial energy equipartition. Using a set of Monte Carlo clusters simulations, we investigate the role of the onset of energy equipartition in shaping the mass-to-light ratio (M/L) in GCs. Our simulations show that the M/L profiles cannot be considered constant and their specific shape strongly depends on the dynamical age of the clusters. Dynamically younger clusters display a central peak up to M/L 25 M /L caused by the retention of dark remnants; this peak flattens out for dynamically older clusters. Moreover, we find that also the global values of M/L correlate with the dynamical state of a cluster quantified as either the number of relaxation times a system has experienced n rel or the equipartition parameter m eq : clusters closer to full equipartition (higher n rel or lower m eq ) display a lower M/L. We show that the decrease of M/L is primarily driven by the dynamical ejection of dark remnants, rather than by the escape of low-mass stars. The predictions of our models are in good agreement with observations of GCs in the Milky Way and M31, indicating that differences in relaxation state alone can explain variations of M/L up to a factor of 3. Our characterization of the M/L as a function of relaxation state is of primary relevance for the application and interpretation of dynamical models.

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Section: Global Relationsmentioning

confidence: 86%

Section: Discussionmentioning

confidence: 99%

The relation between the mass-to-light ratio and the relaxation state of globular clusters

Bianchini

Sills

Ven

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…Leading explanations of why this size difference exists suggest that red and blue clusters have different formation, dynamical and stellar evolution histories (e.g. Kundu & Whitmore 1998;Jordán 2004;Jordán et al 2005;Harris 2009a;Sippel et al 2012;Schulman et al 2012). Here we explore the possibility that the size difference may be due to different orbital anisotropy profiles.…”

Section: Red and Blue Globular Clustersmentioning

confidence: 99%

Globular Cluster Scale Sizes in Giant Galaxies: The Case of M87 and the Role of Orbital Anisotropy and Tidal Filling

Webb

Sills

Harris

2013

ApJ

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We present new Hubble Space Telescope imaging of the outer regions of M87 in order to study its globular cluster (GC) population out to large galactocentric distances. We discuss particularly the relationship between GC effective radii r h and projected galactocentric distance R gc . The observations suggest a shallow trend r h ∝ R 0.14 gc out to R gc ∼ 100 kpc, in agreement with studies of other giant elliptical galaxies. To theoretically reproduce this relationship we simulate GC populations with various distributions of orbits. For an isotropic distribution of cluster orbits we find a steeper trend of r h ∝ R 0.4 gc . Instead we suggest that (a) if the cluster system has an orbital anisotropy profile, where orbits become preferentially radial with increasing galactocentric distance, and (b) if clusters become more tidally under-filling with galactocentric distance, the observed relationship can be recovered. We also apply this approach to the red and blue GC populations separately and predict that red clusters are preferentially under-filling at large R gc and have a more isotropic distribution of orbits than blue clusters.

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“…They are also rather "simple" stellar systems consisting of a distinct population, which is in dynamic equilibrium. Therefore, they are used for extensive N-body simulation in order to understand the formation and evolution of the Milky Way (Sippel et al 2012).…”

Section: Introductionmentioning

confidence: 99%

The first Δa observations of three globular clusters

Paunzen

Iliev

Pintado³

et al. 2014

Monthly Notices of the Royal Astronomical Society

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Globular clusters are main astrophysical laboratories to test and modify evolutionary models. Thought to be rather homogeneous in their local elemental distribution of members, results suggest a wide variety of chemical peculiarities. Besides different main sequences, believed to be caused by different helium abundances, peculiarities of blue horizontal-branch stars and on the red giant branch were found. This whole zoo of peculiar objects has to be explained in the context of stellar formation and evolution. The tool of ∆a photometry is employed in order to detect peculiar stars in the whole spectral range. This three filter narrow band system measures the flux distribution in the region from 4900 to 5600Å in order to find any peculiarities around 5200Å. It is highly efficient to detect classical chemically peculiar stars of the upper main sequence, Be/Ae, shell and metal-weak objects in the Milky Way and Magellanic Clouds. We present ∆a photometry of 2266 stars from 109 individual frames for three globular clusters (NGC 104, NGC 6205, and NGC 7099). A comparison with published abundances, for three horizontal-branch stars, only, yield an excellent agreement. According to the 3σ detection limit of each globular cluster, about 3% of the stars lie in abnormal regions in the diagnostic diagrams. The first observations of three widely different aggregates give very promising results, which will serve as a solid basis for follow-up observations including photometric as well as spectroscopic studies.

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N-body models of globular clusters: metallicities, half-light radii and mass-to-light ratios

Cited by 40 publications

References 77 publications

The relation between the mass-to-light ratio and the relaxation state of globular clusters

The relation between the mass-to-light ratio and the relaxation state of globular clusters

Globular Cluster Scale Sizes in Giant Galaxies: The Case of M87 and the Role of Orbital Anisotropy and Tidal Filling

The first Δa observations of three globular clusters

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