Exploring the impact of a rapidly decelerating bar on transforming bulge orbits into disc-like orbits
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| Main Authors: | , , , , , , , , , |
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| Format: | Preprint |
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2023
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| _version_ | 1866912053645541376 |
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| author | Li, Chengdong Yuan, Zhen Monari, Giacomo Martin, Nicolas F. Siebert, Arnaud Famaey, Benoit Chiba, Rimpei Kordopatis, Georges Ibata, Rodrigo A. Hill, Vanessa |
| author_facet | Li, Chengdong Yuan, Zhen Monari, Giacomo Martin, Nicolas F. Siebert, Arnaud Famaey, Benoit Chiba, Rimpei Kordopatis, Georges Ibata, Rodrigo A. Hill, Vanessa |
| contents | The most metal-poor tail of the Milky Way ([Fe/H] $\leq$ $-$2.5) contains a population of stars with very prograde planar orbits, which is puzzling in both their origin and evolution. A possible scenario is that they are shepherded by the bar from the inner Galaxy, where many of the old and low-metallicity stars in the Galaxy are located. To investigate this scenario, we use test-particle simulations with an axisymmetric background potential plus a central bar model. The test particles are generated by an extended distribution function (EDF) model based on the observational constraints of bulge stars. According to the simulation results, a bar with constant pattern speed cannot help bring stars from the bulge to the solar vicinity. In contrast, when the model includes a rapidly decelerating bar, some bulge stars can gain rotation and move outwards as they are trapped in the co-rotation regions of the bar. The resulting distribution of shepherded stars heavily depends on the present-day azimuthal angle between the bar and the Sun. The majority of the low-metallicity bulge stars driven outwards are distributed in the fourth quadrant of the Galaxy with respect to the Sun, and about 10$\%$ of them are within 6 kpc from us. Our experiments indicate that the decelerating bar perturbation can be a contributing process to explain part of the most metal-poor stars with prograde planar orbits seen in the Solar neighborhood but is unlikely to be the dominant one. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2311_15270 |
| institution | arXiv |
| publishDate | 2023 |
| record_format | arxiv |
| spellingShingle | Exploring the impact of a rapidly decelerating bar on transforming bulge orbits into disc-like orbits Li, Chengdong Yuan, Zhen Monari, Giacomo Martin, Nicolas F. Siebert, Arnaud Famaey, Benoit Chiba, Rimpei Kordopatis, Georges Ibata, Rodrigo A. Hill, Vanessa Astrophysics of Galaxies The most metal-poor tail of the Milky Way ([Fe/H] $\leq$ $-$2.5) contains a population of stars with very prograde planar orbits, which is puzzling in both their origin and evolution. A possible scenario is that they are shepherded by the bar from the inner Galaxy, where many of the old and low-metallicity stars in the Galaxy are located. To investigate this scenario, we use test-particle simulations with an axisymmetric background potential plus a central bar model. The test particles are generated by an extended distribution function (EDF) model based on the observational constraints of bulge stars. According to the simulation results, a bar with constant pattern speed cannot help bring stars from the bulge to the solar vicinity. In contrast, when the model includes a rapidly decelerating bar, some bulge stars can gain rotation and move outwards as they are trapped in the co-rotation regions of the bar. The resulting distribution of shepherded stars heavily depends on the present-day azimuthal angle between the bar and the Sun. The majority of the low-metallicity bulge stars driven outwards are distributed in the fourth quadrant of the Galaxy with respect to the Sun, and about 10$\%$ of them are within 6 kpc from us. Our experiments indicate that the decelerating bar perturbation can be a contributing process to explain part of the most metal-poor stars with prograde planar orbits seen in the Solar neighborhood but is unlikely to be the dominant one. |
| title | Exploring the impact of a rapidly decelerating bar on transforming bulge orbits into disc-like orbits |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2311.15270 |