Kinematics of outer halo globular clusters

• Verfasst von: Koch-Hansen, Andreas [VerfasserIn]
• Verfasst von: Hanke, Michael [VerfasserIn]
• Verfasst von: Kacharov, Nikolay [VerfasserIn]
• Titel: Kinematics of outer halo globular clusters
• Titelzusatz: M 75 and NGC 6426
• Verf.angabe: Andreas Koch, Michael Hanke, and Nikolay Kacharov
• E-Jahr: 2018
• Jahr: 22 August 2018
• Umfang: 9 S.
• Fussnoten: Gesehen am 21.02.2019
• Titel Quelle: Enthalten in: Astronomy and astrophysics
• Ort Quelle: Les Ulis : EDP Sciences, 1969
• Jahr Quelle: 2018
• Band/Heft Quelle: 616(2018) Artikel-Nummer A74, 9 Seiten
• ISSN Quelle: 1432-0746
• DOI: doi:10.1051/0004-6361/201833110
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1587872722

Abstract

Globular clusters (GCs) and their dynamic interactions with the Galactic components provide an important insight into the structure and formation of the early Milky Way. We present a kinematic study of two outer halo GCs based on a combination of VLT/FORS2, VLT/FLAMES, and Magellan/MIKE low- and high-resolution spectroscopy of 32 and 27 member stars, respectively. Although both clusters are located at Galactocentric distances of 15 kpc, they have otherwise very different properties. M 75 is a luminous and metal-rich system at [Fe/H] = 1.2 dex, which is a value that we confirm from the calcium triplet region. This GC shows mild evidence for rotation with an amplitude of 5 km s . One of the most metal-poor GCs in the Milky Way (at [Fe II/H] = dex), NGC 6426 exhibits marginal evidence of internal rotation at the 2 km s level. Both objects have velocity dispersions that are consistent with their luminosity. Although limited by small-number statistics, the resulting limits on their ratios suggest that M 75 is a slow rotator driven by internal dynamics rather than being affected by the weak Galactic tides at its large distances. In this work, M 75 ( ) is fully consistent with the properties of other, younger halo clusters. At , NGC 6426 appears to have a remarkably ordered internal motion for its low metallicity, but the large uncertainty does not allow for an unambiguous categorization as a fast rotator. An accretion origin of M 75 cannot be excluded, based on the eccentric orbit, which we derived from the recent data release 2 of <i>Gaia<i/>, and considering its younger age.