We conduct a quantitative analysis of the star formation history (SFH) of the Milky Way's bulge by exploiting the constraining power of its stellar [Fe/H] and [Mg/Fe] distribution functions. Using APOGEE data, we confirm the previously-established bimodal [Mg/Fe]--[Fe/H] distribution within 3 kpc of the inner Galaxy. Compared to that in the solar vicinity, the high-$\alpha$ population in the bulge peaks at a lower [Fe/H]. To fit these observations, we use a simple but flexible star formation framework, which assumes two distinct stages of gas accretion and star formation, and systematically evaluate a wide multi-dimensional parameter space. We find that the data favor a three-phase SFH that consists of an initial starburst, followed by a rapid star formation quenching episode and a lengthy, quiescent secular evolution phase. The metal-poor, high-$\alpha$ bulge stars ([Fe/H] 0.15) are formed rapidly ( 0.0 and [Mg/Fe]<0.15) then accumulates gradually through inefficient star formation during the secular phase. This is qualitatively consistent with the early SFH of the inner disk. Given this scenario, a notable fraction of young stars (age<5 Gyr) is expected to persist in the bulge. Combined with extragalactic observations, these results suggest that a rapid star formation quenching process is responsible for bimodal distributions in both the Milky Way's stellar populations and in the general galaxy population and thus plays a critical role in galaxy evolution.

中文翻译：

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受双峰化学丰度分布限制的银河系膨胀恒星形成历史

我们利用银河系恒星[Fe/H]和[Mg/Fe]分布函数的约束力，对银河系的恒星形成历史（SFH）进行了定量分析。使用 APOGEE 数据，我们确认了先前建立的双峰 [Mg/Fe]--[Fe/H] 分布在内部星系 3 kpc 内。与太阳附近的相比，凸起中的高 $\alpha$ 群体在较低的 [Fe/H] 处达到峰值。为了适应这些观察，我们使用了一个简单但灵活的恒星形成框架，该框架假设了气体吸积和恒星形成的两个不同阶段，并系统地评估了广泛的多维参数空间。我们发现数据有利于三相 SFH，它由初始星暴组成，然后是快速的恒星形成淬灭阶段和漫长的、静止的长期演化阶段。贫金属，高 $\alpha$ 膨胀星（[Fe/H] 0.15）迅速形成（0.0 和 [Mg/Fe]<0.15），然后在长期阶段通过低效的恒星形成逐渐积累。这与内盘的早期SFH在性质上是一致的。鉴于这种情况，预计有相当一部分年轻恒星（年龄<5 Gyr）将继续存在于凸起中。结合河外观测，这些结果表明，快速的恒星形成淬灭过程是银河系恒星群和一般星系群中双峰分布的原因，因此在星系演化中起着关键作用。这与内盘的早期SFH在性质上是一致的。鉴于这种情况，预计有相当一部分年轻恒星（年龄<5 Gyr）将继续存在于凸起中。结合河外观测，这些结果表明，快速的恒星形成淬灭过程是银河系恒星群和一般星系群中双峰分布的原因，因此在星系演化中起着关键作用。这与内盘的早期SFH在性质上是一致的。鉴于这种情况，预计有相当一部分年轻恒星（年龄<5 Gyr）将继续存在于凸起中。结合河外观测，这些结果表明，快速的恒星形成淬灭过程是银河系恒星群和一般星系群中双峰分布的原因，因此在星系演化中起着关键作用。