The Milky Way’s bulge star formation history as constrained from its bimodal chemical abundance distribution. (arXiv:2007.12179v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Lian_J/0/1/0/all/0/1">Jianhui Lian</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zasowski_G/0/1/0/all/0/1">Gail Zasowski</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hasselquist_S/0/1/0/all/0/1">Sten Hasselquist</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nataf_D/0/1/0/all/0/1">David M. Nataf</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Thomas_D/0/1/0/all/0/1">Daniel Thomas</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bidin_C/0/1/0/all/0/1">Christian Moni Bidin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fernandez_Trincado_J/0/1/0/all/0/1">José G. Fernández-Trincado</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Garcia_Hernandez_D/0/1/0/all/0/1">D. A. Garcia-Hernandez</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lane_R/0/1/0/all/0/1">Richard R. Lane</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Majewski_S/0/1/0/all/0/1">Steven R. Majewski</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Roman_Lopes_A/0/1/0/all/0/1">Alexandre Roman-Lopes</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Schultheis_M/0/1/0/all/0/1">Mathias Schultheis</a>
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]<0.0 and [Mg/Fe]>0.15) are formed
rapidly (<2 Gyr) during the early starburst. The density gap between the high-
and low-$alpha$ sequences is due to the quenching process. The metal-rich,
low-$alpha$ 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 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.
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]<0.0 and [Mg/Fe]>0.15) are formed
rapidly (<2 Gyr) during the early starburst. The density gap between the high-
and low-$alpha$ sequences is due to the quenching process. The metal-rich,
low-$alpha$ 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 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.
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