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The Milky Way's bulge star formation history as constrained from its bimodal chemical abundance distribution

Research output: Contribution to journalArticlepeer-review

  • Jianhui Lian
  • Gail Zasowski
  • Sten Hasselquist
  • David M. Nataf
  • Professor Daniel Thomas
  • Christian Moni Bidin
  • José G. Fernández-Trincado
  • D. A. Garcia-Hernandez
  • Richard R. Lane
  • Steven R. Majewski
  • Alexandre Roman-Lopes
  • Mathias Schultheis
We conduct a quantitative analysis of the star formation history (SFH) of the Milky Way’s (MW) bulge by exploiting the constraining power of its stellar [Fe/H] and [Mg/Fe] distribution functions. Using Apache Point Observatory Galactic Evolution Experiment survey data, we confirm the previously established bimodal [Mg/Fe]–[Fe/H] distribution within 3 kpc of the inner Galaxy. To fit the chemical bimodal distribution, 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 multidimensional parameter space. We find that the data favour 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-α bulge stars ([Fe/H] < 0.0 and [Mg/Fe] > 0.15) are formed rapidly (<2 Gyr) during the early starburst. The density gap between the high- and low-α sequences is due to the quenching process. The metal-rich, low-α population ([Fe/H] > 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 disc. 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 MW’s stellar populations and in the general galaxy population and thus plays a critical role in galaxy evolution.
Original languageEnglish
Pages (from-to)3557-3570
Number of pages14
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Early online date27 Jul 2020
Publication statusPublished - 1 Sep 2020


  • staa2205

    Rights statement: This article has been accepted for publication in MNRAS. © 2020 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

    Final published version, 6.14 MB, PDF document

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