Dynamical Origin of the Vertical Metallicity Gradient of the Milky Way Bulge
A vertical metallicity gradient (VMG) in the Milky Way bulge is well-established. Yet, its origin has not been fully understood under the Galactic secular evolution scenario. We construct single-disk and triple-disk N -body models with an initial radial metallicity gradient (RMG) for each disk. Thes...
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| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2024-01-01
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| Series: | The Astrophysical Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/1538-4357/ad8640 |
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| Summary: | A vertical metallicity gradient (VMG) in the Milky Way bulge is well-established. Yet, its origin has not been fully understood under the Galactic secular evolution scenario. We construct single-disk and triple-disk N -body models with an initial radial metallicity gradient (RMG) for each disk. These models generate a VMG through a “two-step heating” mechanism: the outer, metal-poor particles move inward via the bar instability and subsequently undergo more significant vertical heating during the buckling instability, so they end up at greater vertical height. The “two-step heating” mechanism nearly linearly transforms the RMGs in precursor disks into VMGs. Comparing the models with a triple-disk model tagged with radially independent Gaussian metallicity, we find that, despite certain limitations, the “two-step heating” mechanism is still important in shaping the Galactic VMG. If the bar and buckling instabilities contributed to the formation of boxy/peanut-shaped bulges, then the “two-step heating” mechanism is inevitable in the secular evolution of a boxy/peanut-shaped bulge. |
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| ISSN: | 1538-4357 |