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

Webb, Jeremy J.; Sills, Alison; Harris, William E.

doi:10.1088/0004-637x/779/2/94

Cited by 13 publications

(15 citation statements)

References 54 publications

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“…Nevertheless, the great majority of GCs are smaller than r h ∼ 10 pc; in the Virgo cluster, which lies at a distance of 16.5 Mpc (Mei et al 2005;Blakeslee et al 2009), the average GC half-light radius is 2.7 ± 0.35 pc ∼ 0. 035 , similar results can be found in Webb et al 2013). By contrast, the half-light radii of known UCDs span a range, from 11 pc to 93 pc with a median of ∼ 20 pc or 0.…”

Section: Measurement Of Half-light Radii: Methodologysupporting

confidence: 81%

The Next Generation Virgo Cluster Survey. X. Properties of Ultra-Compact Dwarfs in the M87, M49, and M60 Regions

Liu

Peng

Côté

et al. 2015

ApJ

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We use imaging from the Next Generation Virgo cluster Survey (NGVS) to present a comparative study of ultra-compact dwarf (UCD) galaxies associated with three prominent Virgo sub-clusters: those centered on the massive, red-sequence galaxies M87, M49 and M60. We show how UCDs can be selected with high completeness using a combination of half-light radius and location in color-color diagrams (u * iK s or u * gz). Although the central galaxies in each of these sub-clusters have nearly identical luminosities and stellar masses, we find large differences in the sizes of their UCD populations, with M87 containing ∼ 3.5 and 7.8 times more UCDs than M49 and M60, respectively. The relative abundance of UCDs in the three regions scales in proportion to sub-cluster mass, as traced by X-ray gas mass, total gravitating mass, number of globular clusters, and number of nearby galaxies. We find that the UCDs are predominantly blue in color, with ∼ 85% of the UCDs having colors similar to blue GCs and stellar nuclei of dwarf galaxies. We present evidence that UCDs surrounding M87 and M49 may follow a morphological sequence ordered by the prominence of their outer, low surface brightness envelope, ultimately merging with the sequence of nucleated low-mass galaxies, and that envelope prominence correlates with distance from either galaxy. Our analysis provides evidence that tidal stripping of nucleated galaxies is an important process in the formation of UCDs.

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Section: Measurement Of Half-light Radii: Methodologysupporting

confidence: 81%

The Next Generation Virgo Cluster Survey. X. Properties of Ultra-Compact Dwarfs in the M87, M49, and M60 Regions

Liu

Peng

Côté

et al. 2015

ApJ

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“…The finding that UCDs in the central ∼ 40 kpc are depleted of radial orbits may be partly attributed to a stronger tidal influence at smaller galactocentric distances. To be quantitative, the Jacobi radius r J of a stellar cluster moving in the tidal field of its host galaxy is determined by its galactocentric distance r gal , the galaxy mass M gal interior to r gal and the cluster mass m. Specifically, r J = r gal (m/2M gal ) 1/3 (von Hoerner 1957;Innanen et al 1983;Bertin & Varri 2008;Renaud et al 2011;Webb et al 2013). Based on this basic tidal theory and the Zhu et al mass profile of M87, we estimated the ratio of limiting radius r L to r J as a function of galactocentric distances for M87 UCDs (m = 2×10 6 M ⊙ or 5×10 6 M ⊙ ) with projected half-mass radius r h = 10 pc ( Figure 21).…”

Section: Depletion Of Radial Orbits Of Ucds At Small Galactocentric Dmentioning

confidence: 99%

The Next Generation Virgo Cluster Survey. Vi. The Kinematics of Ultra-Compact Dwarfs and Globular Clusters in M87

Zhang

Peng

Côté

et al. 2015

ApJ

154

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We present the dynamical properties of 97 spectroscopically confirmed ultra-compact dwarfs (UCDs; r h 10 pc) and 911 globular clusters (GCs) associated with central cD galaxy of the Virgo cluster, M87. Our UCDs, of which 89% have M ⋆ 2×10 6 M ⊙ and 92% are as blue as the classic blue GCs, nearly triple previously confirmed sample of Virgo UCDs, providing by far the best opportunity for studying global dynamics of UCDs. We found that (1) UCDs have a surface number density profile that is shallower than that of blue GCs in the inner ∼ 70 kpc and as steep as that of red GCs at larger radii; (2) UCDs exhibit a significantly stronger rotation than GCs, and blue GCs seem to have a velocity field that is more consistent with that of the surrounding dwarf ellipticals than with that of UCDs; (3) UCDs have an orbital anisotropy profile that is tangentially-biased at radii 40 kpc and radially-biased further out, whereas blue GCs become more tangentially-biased at larger radii beyond ∼ 40 kpc; (4) GCs with M ⋆ 2×10 6 M ⊙ have rotational properties indistinguishable from the less massive ones, suggesting that it is the size, instead of mass, that differentiates UCDs from GCs as kinematically distinct populations. We conclude that most UCDs in M87 are not consistent with being merely the most luminous and extended examples of otherwise normal GCs. The radiallybiased orbital structure of UCDs at large radii is in general agreement with the "tidally threshed dwarf galaxy" scenario.

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“…Additionally, even though cluster sizes are measured in different wave bands, many studies have found that there are minimal differences when comparing sizes measured with different filters (e.g. Harris 2010;Strader et al 2012;Webb et al 2013b). And, since similar constraints are used to confirm GC candidates and minimize contaminants (magnitude, colour, quality of fit, and size), the observational datasets are as homogeneous as possible.…”

Section: Observationsmentioning

confidence: 99%

“…M87 is a giant elliptical galaxy located at the centre of the Virgo cluster, with a distance modulus of (m − M )0 = 30.88 (Pierce et al 1994;Tonry et al 2001 Webb et al (2012) and Webb et al (2013b) for a detailed description of how cluster candidates are selected and sizes are measured.…”

Section: M87mentioning

confidence: 99%

“…In two previous studies of the giant elliptical galaxy M87 (Webb et al 2012(Webb et al , 2013b, we explored the effects of orbital anisotropy and tidal filling on its GC population out to 110 kpc. We found that it was possible to reproduce the observed relationship between r h and Rgc in M87 by allowing cluster orbits to be preferentially radial.…”

Section: Introductionmentioning

confidence: 99%

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Globular cluster scale sizes in giant galaxies: orbital anisotropy and tidally underfilling clusters in M87, NGC 1399 and NGC 5128

Webb

Sills

Harris

et al. 2016

Mon. Not. R. Astron. Soc.

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We investigate the shallow increase in globular cluster half-light radii with projected galactocentric distance R gc observed in the giant galaxies M87, NGC 1399, and NGC 5128. To model the trend in each galaxy, we explore the effects of orbital anisotropy and tidally under-filling clusters. While a strong degeneracy exists between the two parameters, we use kinematic studies to help constrain the distance R β beyond which cluster orbits become anisotropic, as well as the distance R f α beyond which clusters are tidally under-filling. For M87 we find R β > 27 kpc and 20 < R f α < 40 kpc and for NGC 1399 R β > 13 kpc and 10 < R f α < 30 kpc. The connection of R f α with each galaxy's mass profile indicates the relationship between size and R gc may be imposed at formation, with only inner clusters being tidally affected. The best fitted models suggest the dynamical histories of brightest cluster galaxies yield similar present-day distributions of cluster properties. For NGC 5128, the central giant in a small galaxy group, we find R β > 5 kpc and R f α > 30 kpc. While we cannot rule out a dependence on R gc , NGC 5128 is well fitted by a tidally filling cluster population with an isotropic distribution of orbits, suggesting it may have formed via an initial fast accretion phase. Perturbations from the surrounding environment may also affect a galaxy's orbital anisotropy profile, as outer clusters in M87 and NGC 1399 have primarily radial orbits while outer NGC 5128 clusters remain isotropic.

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

Cited by 13 publications

References 54 publications

The Next Generation Virgo Cluster Survey. X. Properties of Ultra-Compact Dwarfs in the M87, M49, and M60 Regions

The Next Generation Virgo Cluster Survey. X. Properties of Ultra-Compact Dwarfs in the M87, M49, and M60 Regions

The Next Generation Virgo Cluster Survey. Vi. The Kinematics of Ultra-Compact Dwarfs and Globular Clusters in M87

Globular cluster scale sizes in giant galaxies: orbital anisotropy and tidally underfilling clusters in M87, NGC 1399 and NGC 5128

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