Orbits of Globular Clusters in the Outer Galaxy: NGC 7006

Abstract

We present a proper motion study of the distant globular cluster NGC 7006 based on the measurement of 25 photographic plates spanning a 40-year interval. The absolute proper motion determined with respect to extragalactic objects is (-0.96, -1.14) +- (0.35, 0.40) mas/yr. The total space velocity of NGC 7006 in a Galactocentric rest frame is 279 km/s, placing the cluster on one of the most energetic orbits (Ra =102 kpc) known to date for clusters within 40-kpc from the Galactic center. We compare the orbits of four clusters that have apocentric radii larger than 80 kpc (NGC 5466, NGC 6934, NGC 7006 and Pal 13) with those of Galactic satellites with well-measured proper motions. These clusters have orbits that are highly eccentric and of various inclinations with respect to the Galactic plane. In contrast, the orbits of the Galactic satellites are of low to moderate eccentricity and highly inclined. Based on orbit types, chemical abundances and cluster parameters, we discuss the properties of the hypothetical host systems of the remote globular clusters in the Searle-Zinn paradigm. It is apparent that clusters such as NGC 5466, NGC 6934 and NGC 7006 formed in systems that more likely resemble the Fornax dSph, rather than the Sagittarius dSph. We also discuss plausible causes for the difference found so far between the orbit type of outer halo clusters and that of Galactic satellites and for the tentative, yet suggestive phase-space scatter found among outer halo clusters.

27 pages, 5 figures, to be published in the Astronomical Journal

References in corpus (7)

• A giant stream of metal-rich stars in the halo of the galaxy M31
• Abundance Patterns in the Draco, Sextans and Ursa Minor Dwarf Spheroidal Galaxies
• Galactic Globular Cluster Relative Ages
• Constraining the History of the Sagittarius Dwarf Galaxy Using Observations of its Tidal Debris
• The Absolute Proper Motion of Palomar 12: A Case for Tidal Capture from the Sagittarius Dwarf Spheroidal Galaxy
• Palomar 13's Last Stand
• Young Globular Clusters and Dwarf Spheroidals

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