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

Abstract

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 $r_h\propto R_{gc}^{0.14}$ out to $R_{gc}\sim 100$ 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 $r_h\propto R_{gc}^{0.4}$. 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.

10 pages, 11 figures, Accepted for publication in ApJ

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Cited by in corpus (11)

• The Next Generation Virgo Cluster Survey. VI. The Kinematics of Ultra-compact Dwarfs and Globular Clusters in M87
• 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. V. modelling the dynamics of M87 with the Made-to-Measure method
• Mass Evaporation Rate of Globular Clusters in a Strong Tidal Field
• The Strikingly Metal-Rich Halo of the Sombrero Galaxy
• MOCCA Survey Database: Extra Galactic Globular Clusters. I. Method and first results
• Globular Cluster Scale Sizes in Giant Galaxies: Orbital Anisotropy and Tidally Under-filling Clusters in M87, NGC 1399, and NGC 5128
• Made-to-Measure Modelling of Globular Clusters
• Bayesian Inference of Globular Cluster Properties Using Distribution Functions
• Hierarchical Bayesian Inference of Globular Cluster Properties
• Evidence for Environmental Stripping in the Coma Cluster