The chemical properties of the Milky Way’s on-bar and off-bar regions: evidence for inhomogeneous star formation history in the bulge
The chemical properties of the Milky Way’s on-bar and off-bar regions: evidence for inhomogeneous star formation history in the bulge
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DOI：
10.1093/mnras/staa3256
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发表时间：
2020-08
影响因子：
4.8
通讯作者：
J. Lian;G. Zasowski;S. Hasselquist;J. Neumann;S. Majewski;R. Cohen;J. Fernández-Trincado;R. Lane;P. Longa-Peña;A. Roman-Lopes
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文献类型：
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作者：
J. Lian;G. Zasowski;S. Hasselquist;J. Neumann;S. Majewski;R. Cohen;J. Fernández-Trincado;R. Lane;P. Longa-Peña;A. Roman-Lopes
大量的综合星光、恒星计数和运动学的研究已经证实银河系是一个棒星系。然而，很少有研究调查了酒吧的恒星人口属性，这携带了关于酒吧的形成历史有价值的独立信息。在这里，我们进行了详细的分析化学丰度分布（[Fe/H]和[Mg/Fe]）在酒吧和酒吧区研究的方位角变化的星星形成历史（SFH）在银河系内部。我们发现，银心半径为3 kpc < rGC < 5 kpc的棒上星和棒外星具有非常一致的[Fe/H]和[Mg/Fe]分布函数以及[Mg/Fe]-[Fe/H]关系，表明长棒和盘具有共同的SFH。相比之下，在较小的半径（2 kpc < rGC < 3 kpc）的酒吧和光盘显示出明显的差异，相对更多的非常富含金属（$\rm [Fe/H] \sim 0.4$）的恒星，但较少的太阳丰度的恒星在酒吧。鉴于Lian等人提出的内星系三阶段星星形成历史，这些差异可以通过离杆盘经历更快的早期淬火过程或最近的贫金属气体堆积来解释。小rGC丰度分布的垂直变化表明，棒中低α星的垂直分布范围更广，这可能是棒屈曲过程中垂直加热的化学证据。在凸出部外部缺乏这种垂直变化则可能暗示在长杆中缺乏垂直加热。
Numerous studies of integrated starlight, stellar counts, and kinematics have confirmed that the Milky Way is a barred galaxy. However, far fewer studies have investigated the bar’s stellar population properties, which carry valuable independent information regarding the bar’s formation history. Here, we conduct a detailed analysis of chemical abundance distributions ([Fe/H] and [Mg/Fe]) in the on-bar and off-bar regions to study the azimuthal variation of star formation history (SFH) in the inner Galaxy. We find that the on-bar and off-bar stars at Galactocentric radii 3 kpc < rGC < 5 kpc have remarkably consistent [Fe/H] and [Mg/Fe] distribution functions and [Mg/Fe]–[Fe/H] relation, suggesting a common SFH shared by the long bar and the disc. In contrast, the bar and disc at smaller radii (2 kpc < rGC < 3 kpc) show noticeable differences, with relatively more very metal-rich ($\rm [Fe/H] \sim 0.4$) stars but fewer solar abundance stars in the bar. Given the three-phase star formation history proposed for the inner Galaxy in Lian et al., these differences could be explained by the off-bar disc having experienced either a faster early quenching process or recent metal-poor gas accretion. Vertical variations of the abundance distributions at small rGC suggest a wider vertical distribution of low-α stars in the bar, which may serve as chemical evidence for vertical heating through the bar buckling process. The lack of such vertical variations outside the bulge may then suggest a lack of vertical heating in the long bar.