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.

中文翻译：

---

从盖亚数据第 3 版洞察银河核球化学动力学特性


我们使用盖亚数据版本 3 中的红巨星探索了星系在方位角速度 V _ϕ 和金属丰度 [Fe/H] 空间中的化学动力学特性。行归一化 V _ϕ –[Fe/H]图形成从凸起到外盘的连贯序列，清楚地揭示了薄/厚盘和飞溅。富含金属的恒星表现出棒状运动学，而缺乏金属的恒星则表现出色散主导的运动学。中间金属丰度群体 (−1 < [Fe/H]< − 0.4) 可以分为两个群体，一个是条状的，即动态冷的 (σVR∼80 km s ⁻¹ )和快速旋转（V _ϕ ≳ 100 km s ⁻¹ ），以及动态热（σVR∼110 km s ⁻¹ ）和慢速的 Splash -旋转（V _ϕ ≲ 100 km s ⁻¹ ）。我们将核球区域的观测结果与 Auriga 模拟进行比较，其中最后一次重大合并事件发生在 ∼10 Gyr 之前：只有在合并期间诞生的恒星才在 V _ϕ 中显示出类似飞溅的特征 – [Fe/H]空间，表明飞溅很可能是合并引起的，主要由加热的盘状恒星和与最后一次主要合并相关的星暴组成。由于飞溅是由原盘形成的，其金属丰度下限与厚盘的金属丰度下限一致。随后由 [Fe/H] > − 1 dex 的动态热盘形成条，飞溅不参与条的形成和生长。此外，通过一组孤立演化的 N 体盘模拟，我们证实非旋转经典核球可以通过棒旋转并发展圆柱旋转，这与对贫金属恒星的观测结果一致。