Funakoshi, Natsuki;
Kawata, Daisuke;
Sanders, Jason L;
Ciucă, Ioana;
Grand, Robert JJ;
Zhāng, HanYuan;
(2025)
Thick-to-thin disc transition and gas disc shrinking induced by the Gaia-Sausage-Enceladus merger.
Monthly Notices of the Royal Astronomical Society
, Article staf1632. 10.1093/mnras/staf1632.
(In press).
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Abstract
Understanding the Milky Way disc formation requires characterising its structural and kinematic properties as functions of stellar age. Using red giant stars from APOGEE DR17 and Gaia DR3, we model the age-dependent stellar kinematics with a quasi-isothermal distribution function and fit disc parameters as a function of age using non-parametric splines. We identify a transition from thick to thin disc populations around 10 Gyr ago. Stars older than this have short scale lengths (∼1.7 kpc), typical of the thick disc, while younger stars exhibit increasing scale length with decreasing age, consistent with inside-out formation of the thin disc. This transition possibly coincides with the end of the starburst triggered by the Gaia-Sausage-Enceladus (GSE) merger. Stars formed around 10 Gyr ago exhibit a dip in scale length, even shorter than that of the thick disc. Comparison with an Auriga simulation suggests that this scale-length dip reflects gas disc shrinking caused by the transition from a cold to hot gas accretion mode. We propose the following disc formation scenario: (1) the thick disc formed under cold-mode accretion; (2) the GSE merger triggered a starburst and increased the total mass of the Galaxy, causing the transition to hot-mode accretion; (3) rapid gas consumption led to temporary shrinking of the star-forming gas disc; and then (4) thin disc grows in an inside-out fashion, as the size of the star-forming gas disc grows via hot-mode smooth gas accretion.
| Type: | Article |
|---|---|
| Title: | Thick-to-thin disc transition and gas disc shrinking induced by the Gaia-Sausage-Enceladus merger |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1093/mnras/staf1632 |
| Publisher version: | https://doi.org/10.1093/mnras/staf1632 |
| Language: | English |
| Additional information: | © The Author(s) 2025. Published by Oxford University Press on behalf of The Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. |
| Keywords: | Galaxy: disc, Galaxy: evolution, Galaxy: kinematics and dynamics |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10214846 |
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