The age-chemical abundance structure of the Galactic disc II: $alpha$-dichotomy and thick disc formation. (arXiv:2007.03687v1 [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:+Thomas_D/0/1/0/all/0/1">Daniel Thomas</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Maraston_C/0/1/0/all/0/1">Claudia Maraston</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Beers_T/0/1/0/all/0/1">Timothy C. Beers</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. García-Hernández</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:+Munoz_R/0/1/0/all/0/1">Ricardo R. Munoz</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nitschelm_C/0/1/0/all/0/1">Christian Nitschelm</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:+Zamora_O/0/1/0/all/0/1">Olga Zamora</a>
We extend our previous work on the age-chemical abundance structure of the
Galactic outer disc to the inner disc (4 < r < 8 kpc) based on Apache Point
Observatory Galactic Evolution Experiment (APOGEE) spectroscopic survey.
Different from the outer disc, the inner disc stars exhibit a clear bimodal
distribution in the [Mg/Fe]-[Fe/H] plane. While a number of scenarios have been
proposed in the literature, it remains challenging to recover this bimodal
distribution with theoretical models. To this end, we present a chemical
evolution model embedding a complex multi-phase inner disc formation scenario
that matches the observed bimodal [Mg/Fe]-[Fe/H] distribution.In this scenario,
the formation of the inner disc is dominated by two main starburst episodes 6
Gyr apart with secular, low-level star formation activity in between. In our
model, the first starburst occurs at early cosmic times (t~1 Gyr) and the
second one 6 Gyr later at a cosmic time of t~7 Gyr. Both these starburst
episodes are associated with gas accretion events in our model, and are
quenched rapidly. The first starburst leads to the formation of the
high-$alpha$ sequence, and the second starburst leads to the formation of the
metal-poor low-$alpha$ sequence. The metal-rich low-$alpha$ stars, instead,
form during the secular evolution phase between the two bursts. Our model shows
that the $alpha$-dichotomy originates from the rapid suppression of star
formation after the first starburst. The two starburst episodes are likely to
be responsible for the formation of the geometric thick disc (z >1 kpc), with
the old inner thick disc and the young outer thick disc forming during the
first and the second starbursts, respectively.
We extend our previous work on the age-chemical abundance structure of the
Galactic outer disc to the inner disc (4 < r < 8 kpc) based on Apache Point
Observatory Galactic Evolution Experiment (APOGEE) spectroscopic survey.
Different from the outer disc, the inner disc stars exhibit a clear bimodal
distribution in the [Mg/Fe]-[Fe/H] plane. While a number of scenarios have been
proposed in the literature, it remains challenging to recover this bimodal
distribution with theoretical models. To this end, we present a chemical
evolution model embedding a complex multi-phase inner disc formation scenario
that matches the observed bimodal [Mg/Fe]-[Fe/H] distribution.In this scenario,
the formation of the inner disc is dominated by two main starburst episodes 6
Gyr apart with secular, low-level star formation activity in between. In our
model, the first starburst occurs at early cosmic times (t~1 Gyr) and the
second one 6 Gyr later at a cosmic time of t~7 Gyr. Both these starburst
episodes are associated with gas accretion events in our model, and are
quenched rapidly. The first starburst leads to the formation of the
high-$alpha$ sequence, and the second starburst leads to the formation of the
metal-poor low-$alpha$ sequence. The metal-rich low-$alpha$ stars, instead,
form during the secular evolution phase between the two bursts. Our model shows
that the $alpha$-dichotomy originates from the rapid suppression of star
formation after the first starburst. The two starburst episodes are likely to
be responsible for the formation of the geometric thick disc (z >1 kpc), with
the old inner thick disc and the young outer thick disc forming during the
first and the second starbursts, respectively.
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