Searching for a kinematic signature of the moderately metal-poor stars in the Milky Way bulge using N-body simulations
Abstract
Although there is consensus that metal-rich stars in the Milky Way bulge are formed via secular evolution of the thin disc, the origin of their metal-poor counterparts is still under debate. Two different origins have been invoked for metal-poor stars: they might be classical bulge stars or stars formed via internal evolution of a massive thick disc. We use N-body simulations to calculate the kinematic signature given by the difference in the mean Galactocentric radial velocity (ΔVGC) between metal-rich stars ([Fe/H] ≥ 0) and moderately metal-poor stars (-1.0 ≤ [Fe/H] < 0) in two models, one containing a thin disc and a small classical bulge (B/D = 0.1), and the other containing a thin disc and a massive centrally concentrated thick disc. We reasonably assume that thin-disk stars in each model may be considered as a proxy of metal-rich stars. Similarly, bulge stars and thick-disc stars may be considered as a proxy of metal-poor stars. We calculate ΔVGC at different latitudes (b = 0°, - 2°, - 4°, - 6°, - 8° and - 10°) and longitudes (l = 0°, ± 5°, ± 10° and ± 15°) and show that the ΔVGC trends predicted by the two models are different. We compare the predicted results with ARGOS data and APOGEE DR13 data and show that moderately metal-poor stars are well reproduced with the co-spatial stellar discs model, which has a massive thick disc. Our results give more evidence against the scenario that most of the metal-poor stars are classical bulge stars. If classical bulge stars exists, most of them probably have metallicities [Fe/H] < -1 dex, and their contribution to the mass of the bulge should be a small percentage of the total bulge mass.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- July 2018
- DOI:
- 10.1051/0004-6361/201732568
- arXiv:
- arXiv:1803.09626
- Bibcode:
- 2018A&A...615A.100G
- Keywords:
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- methods: numerical;
- Galaxy: bulge;
- Galaxy: kinematics and dynamics;
- Galaxy: structure;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 7 pages, 4 figures, accepted for publication in A&