Classifying globular clusters and applying them to estimate the mass of the Milky Way

GuangChen Sun, Yougang Wang, Chao Liu Chao Liu, Richard John Long, Xuelei Chen, Qi Gao

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We combine the kinematics of 159 globular clusters (GCs) provided by the Gaia
Early Data Release 3 (EDR 3) with other observational data to classify the GCs, and to
estimate the mass of Milky Way (MW). We use the age-metallicity relation, integrals of
motion, action space and the GC orbits to identify the GCs as either formed in-situ (Bulge
and Disk) or ex-situ (via accretion). We find that 45.3% have formed in-situ, 38.4% may be
related to known merger events: Gaia-Sausage-Enceladus, the Sagittarius dwarf galaxy, the Helmi streams, the Sequoia galaxy, and the Kraken galaxy. We also further identify three new sub-structures associated with the Gaia-Sausage-Enceladus. The remaining 16.3% of GCs are unrelated to the known mergers and thought to be from small accretion events. We select 46 GCs which have the radii 8.0 < r < 37.3 kpc and obtain the anisotropy parameter β = 0.315+0.055−0.049 , which is lower than the recent result using the sample of GCs in Gaia Data Release 2, but still in agreement with it by considering the error bar. By using the same sample, we obtain the MW mass inside the outermost GC as M (< 37.3 kpc) = +0.02+0.423−0.02 × 10^12 M , and the corresponding M200 = 1.11+0.25
−0.18 . The estimated mass is consistent with the results in many recent studies. We also find that the estimated β and mass depend on the selected sample of GCs. However, it is difficult to determine whether a GC fully traces the potential of the MW.
Original languageEnglish
JournalResearch in Astronomy and Astrophysics
Early online date28 Oct 2022
Publication statusE-pub ahead of print - 28 Oct 2022


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