Insights into the Galactic Bulge Chemodynamical Properties from Gaia Data Release 3

Liao, Xiaojie; Li, Zhao-Yu; Simion, Iulia; Shen, Juntai; Grand, Robert; Fragkoudi, Francesca; Marinacci, Federico

Abstract

We explore the chemodynamical properties of the Galaxy in the azimuthal velocity V ϕ and metallicity [Fe/H] space using red giant stars from Gaia Data Release 3. The row-normalized V ϕ –[Fe/H] maps form a coherent sequence from the bulge to the outer disk, clearly revealing the thin/thick disk and the Splash. The metal-rich stars display bar-like kinematics, while the metal-poor stars show dispersion-dominated kinematics. The intermediate-metallicity population (−1 < [Fe/H]< − 0.4) can be separated into two populations, one that is bar-like, i.e., dynamically cold ( σVR∼80 km s−1) and fast-rotating (V ϕ ≳ 100 km s−1), and the Splash, which is dynamically hot ( σVR∼110 km s−1) and slow-rotating (V ϕ ≲ 100 km s−1). We compare the observations in the bulge region with an Auriga simulation where the last major merger event occurred ∼10 Gyr ago: only stars born around the time of the merger reveal a Splash-like feature in the V ϕ –[Fe/H] space, suggesting that the Splash is likely merger-induced, predominantly made up of heated disk stars and the starburst associated with the last major merger. Since the Splash formed from the proto-disk, its lower metallicity limit coincides with that of the thick disk. The bar formed later from the dynamically hot disk with [Fe/H] > − 1 dex, with the Splash not participating in the bar formation and growth. Moreover, with a set of isolated evolving N-body disk simulations, we confirm that a nonrotating classical bulge can be spun up by the bar and develop cylindrical rotation, consistent with the observations for the metal-poor stars.

Citation

Liao, X., Li, Z., Simion, I., Shen, J., Grand, R., Fragkoudi, F., & Marinacci, F. (2024). Insights into the Galactic Bulge Chemodynamical Properties from Gaia Data Release 3. Astrophysical Journal, 967(5), Article 1. https://doi.org/10.3847/1538-4357/ad38ba

• Journal Article Type: Article
• Acceptance Date: Mar 26, 2024
• Online Publication Date: May 13, 2024
• Publication Date: May 13, 2024
• Deposit Date: May 21, 2024
• Publicly Available Date: May 21, 2024
• Journal: Astrophysical Journal
• Print ISSN: 0004-637X
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 967
• Issue: 5
• Article Number: 1
• DOI: https://doi.org/10.3847/1538-4357/ad38ba
• Keywords: Galactic bulge, Galaxy bulges, Milky Way evolution
• Public URL: https://durham-repository.worktribe.com/output/2453439