The Observational and Theoretical Tidal Radii of Globular Clusters in M87

Abstract

Globular clusters have linear sizes (tidal radii) which theory tells us are determined by their masses and by the gravitational potential of their host galaxy. To explore the relationship between observed and expected radii, we utilize the globular cluster population of the Virgo giant M87. Unusually deep, high signal-to-noise images of M87 are used to measure the effective and limiting radii of approximately 2000 globular clusters. To compare with these observations, we simulate a globular cluster population that has the same characteristics as the observed M87 cluster population. Placing these simulated clusters in the well-studied tidal field of M87, the orbit of each cluster is solved and the theoretical tidal radius of each cluster is determined. We compare the predicted relationship between cluster size and projected galactocentric distance to observations. We find that for an isotropic distribution of cluster velocities, theoretical tidal radii are approximately equal to observed limiting radii for Rgc < 10 kpc. However, the isotropic simulation predicts a steep increase in cluster size at larger radii, which is not observed in large galaxies beyond the Milky Way. To minimize the discrepancy between theory and observations, we explore the effects of orbital anisotropy on cluster sizes, and suggest a possible orbital anisotropy profile for M87 which yields a better match between theory and observations. Finally, we suggest future studies which will establish a stronger link between theoretical tidal radii and observed radii.

8 pages, 8 figures, Accepted for publication in ApJ

References in corpus (14)

• Lifetimes of tidally limited star clusters with different radii
• HST/ACS Wide-Field Photometry of the Sombrero Galaxy Globular Cluster System
• Globular Cluster Systems in Giant Ellipticals: the Mass/Metallicity Relation
• The Inner Halo of M87: A First Direct View of the Red-Giant Population
• Structural parameters for globular clusters in M31 and generalizations for the fundamental plane
• On the mass-radius relation of hot stellar systems
• Space Velocities of Southern Globular Clusters. V. A Low Galactic Latitude Sample
• Star Clusters with Primordial Binaries: II. Dynamical Evolution of Models in a Tidal Field
• Structural parameters for globular clusters in NGC 5128. III. ACS surface-brightness profiles and model fits
• The construction of non-spherical models of quasi-relaxed stellar systems
• A Subaru/Suprime-Cam wide-field survey of globular cluster populations around M87 - II: Colour and spatial distribution
• Sizes of Confirmed Globular Clusters in NGC 5128: A Wide-Field High-Resolution Study
• Calibration of BVRI Photometry for the Wide Field Channel of the HST Advanced Camera for Surveys
• Dark Matter Halos: Velocity Anisotropy -- Density Slope Relation

Cited by in corpus (10)

• The Influence of Orbital Eccentricity on Tidal Radii of Star Clusters
• The SLUGGS Survey: Wide Field Imaging of the Globular Cluster System of NGC 4278
• Wide-Field Hubble Space Telescope Observations of the Globular Cluster System in NGC1399
• The Effects of Orbital Inclination on the Scale Size and Evolution of Tidally Filling Star Clusters
• The state of globular clusters at birth: emergence from the gas-embedded phase
• Deep Chandra Monitoring Observations of NGC 4649: II. Wide-Field Hubble Space Telescope Imaging of the Globular Clusters
• Constraining the initial conditions of globular clusters using their radius distribution
• Globular Cluster Scale Sizes in Giant Galaxies: The Case of M87 and the Role of Orbital Anisotropy and Tidal Filling
• The Size Difference Between Red And Blue Globular Clusters Is NOT Due To Projection Effects
• Globular Cluster Scale Sizes in Giant Galaxies: Orbital Anisotropy and Tidally Under-filling Clusters in M87, NGC 1399, and NGC 5128