当Milky Way关灯时：APOGEE提供了我们银河系恒星形成淬灭的证据
When the Milky Way turned off the lights: APOGEE provides evidence of star formation quenching in our Galaxy
摘要：
淬火，即恒星形成的停止，是星系生命周期中最重要的事件之一。我们在这里展示的第一个证据表明，银河系经历了广泛的淬火其恒星形成结束时，其厚盘形成$\sim$ 9 Gyr前。作为APOGEE巡天的一部分，对恒星元素丰度的研究确实揭示了，在小于$\sim$ 2 Gyr的时间里，我们银河系的恒星形成率下降了一个数量级。由于年龄和α丰度之间的紧密相关性，这一事件反映在[Fe/H]-[ $α$ /Fe]平面内的内部盘序列上缺乏恒星。在这个持续约1.5 Gyr的阶段之前，银河系正在活跃地形成恒星。随后，星阵又恢复到了一个低得多的层次，形成了薄盘。这些事件与最近在高红移观测到的MW型祖星非常吻合。在晚型星系中，猝灭被认为与长期的气体耗尽有关。在我们的银河系中，它发生在一个更短的时间尺度上，而淬灭前后的化学连续性表明，它不是由于气体的耗尽。虽然淬火通常与球状体有关，但我们的研究结果表明，它也发生在像银河系这样的星系中，可能是当它们正在经历从厚到薄的圆盘的形态转变时。考虑到晚型星系在当地宇宙中的人口统计，其中经典的凸起是罕见的，我们进一步建议，这可能普遍适用于质量低于或接近$M^*$的星系，淬火可能是厚盘形成的直接后果。我们强调，在银河系的淬火阶段可能是同期的，并与酒吧的形成。我们勾勒出一个场景，一个强大的酒吧可能会抑制恒星的形成。
英文摘要：
Quenching, the cessation of star formation, is one of the most significant events in the life cycle of galaxies. We show here the first evidence that the Milky Way experienced a generalised quenching of its star formation at the end of its thick disk formation $\sim$9 Gyr ago. Elemental abundances of stars studied as part of the APOGEE survey reveal indeed that in less than $\sim$2 Gyr the star formation rate in our Galaxy dropped by an order-of-magnitude. Because of the tight correlation between age and alpha abundance, this event reflects in the dearth of stars along the inner disk sequence in the [Fe/H]-[$α$/Fe] plane. Before this phase, which lasted about 1.5 Gyr, the Milky Way was actively forming stars. Afterwards, the star formation resumed at a much lower level to form the thin disk. These events are very well matched by the latest observation of MW-type progenitors at high redshifts. In late type galaxies, quenching is believed to be related to a long and secular exhaustion of gas. In our Galaxy, it occurred on a much shorter time scale, while the chemical continuity before and after the quenching indicates that it was not due to the exhaustion of the gas. While quenching is generally associated with spheroids, our results show that it also occurs in galaxies like the Milky Way, possibly when they are undergoing a morphological transition from thick to thin disks. Given the demographics of late type galaxies in the local universe, in which classical bulges are rare, we suggest further that this may hold true generally in galaxies with mass lower than or approximately $M^*$, where quenching could be directly a consequence of thick disk formation. We emphasize that the quenching phase in the Milky Way could be contemporaneous with, and related to, the formation of the bar. We sketch a scenario on how a strong bar may inhibit star formation.
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