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|Title:||Globular cluster scale sizes in giant galaxies: orbital anisotropy and tidally underfilling clusters in M87, NGC 1399 and NGC 5128||Authors:||Webb, Jeremy J.
Harris, William E.
Woodley, Kristin A.
Puzia, Thomas H.
|Issue Date:||2016||Journal:||MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY||Number:||460||Issue:||2||First Page:||2129||Abstract:||We investigate the shallow increase in globular cluster half-light radii with projected galactocentric distance R<SUB>gc</SUB> 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 underfilling clusters. While a strong degeneracy exists between the two parameters, we use kinematic studies to help constrain the distance R<SUB>β</SUB> beyond which cluster orbits become anisotropic, as well as the distance R<SUB>fα</SUB> beyond which clusters are tidally underfilling. For M87 we find R<SUB>β</SUB> > 27 kpc and 20 < R<SUB>fα</SUB> < 40 kpc and for NGC 1399 R<SUB>β</SUB> > 13 kpc and 10 < R<SUB>fα</SUB> < 30 kpc. The connection of R<SUB>fα</SUB> with each galaxy's mass profile indicates the relationship between size and R<SUB>gc</SUB> may be imposed at formation, with only inner clusters being tidally affected. The best-fitting 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<SUB>β</SUB> > 5 kpc and R<SUB>fα</SUB> > 30 kpc. While we cannot rule out a dependence on R<SUB>gc</SUB>, 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.||URI:||http://hdl.handle.net/20.500.12386/26427||URL:||https://academic.oup.com/mnras/article/460/2/2129/2609101||ISSN:||0035-8711||DOI:||10.1093/mnras/stw1115||Bibcode ADS:||2016MNRAS.460.2129W||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
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checked on Sep 21, 2020
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