The Milky Way's bulge star formation history as constrained from its bimodal chemical abundance distribution. Issue 3 (27th July 2020)

• Record Type: Journal Article
• Authors: Lian, Jianhui; Zasowski, Gail; Hasselquist, Sten; Nataf, David M; Thomas, Daniel; Moni Bidin, Christian; Fernández-Trincado, José G; Garcia-Hernandez, D A; Lane, Richard R; Majewski, Steven R; Roman-Lopes, Alexandre; Schultheis, Mathias
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 497:Issue 3(2020)
• Page Start: 3557
• Page End: 3570
• Publication Date: 2020-07-27
• Subjects: Galaxy: abundances -- Galaxy: bulge -- Galaxy: evolution -- Galaxy: formation -- Galaxy: stellar content -- Galaxy: structure; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa2205
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: 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.