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The bursty origin of the Milky Way thick disc

Yu, Sijie and Bullock, James S. and Klein, Courtney and Stern, Jonathan and Wetzel, Andrew and Ma, Xiangcheng and Moreno, Jorge and Hafen, Zachary and Gurvich, Alexander B. and Hopkins, Philip F. and Kereš, Dušan and Faucher-Giguère, Claude-André and Feldmann, Robert and Quataert, Eliot (2021) The bursty origin of the Milky Way thick disc. Monthly Notices of the Royal Astronomical Society, 505 (1). pp. 889-902. ISSN 0035-8711. doi:10.1093/mnras/stab1339.

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We investigate thin and thick stellar disc formation in Milky Way-mass galaxies using 12 FIRE-2 cosmological zoom-in simulations. All simulated galaxies experience an early period of bursty star formation that transitions to a late-time steady phase of near-constant star formation. Stars formed during the late-time steady phase have more circular orbits and thin-disc-like morphology at z = 0, while stars born during the bursty phase have more radial orbits and thick-disc structure. The median age of thick-disc stars at z = 0 correlates strongly with this transition time. We also find that galaxies with an earlier transition from bursty to steady star formation have a higher thin-disc fractions at z = 0. Three of our systems have minor mergers with Large Magellanic Cloud-size satellites during the thin-disc phase. These mergers trigger short starbursts but do not destroy the thin disc nor alter broad trends between the star formation transition time and thin/thick-disc properties. If our simulations are representative of the Universe, then stellar archaeological studies of the Milky Way (or M31) provide a window into past star formation modes in the Galaxy. Current age estimates of the Galactic thick disc would suggest that the Milky Way transitioned from bursty to steady phase ∼6.5 Gyr ago; prior to that time the Milky Way likely lacked a recognizable thin disc.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper ItemGIZMO Code ItemFIRE project ItemSoftware Packages ItemSoftware Packages
Yu, Sijie0000-0002-1019-0341
Bullock, James S.0000-0003-4298-5082
Klein, Courtney0000-0002-2762-4046
Stern, Jonathan0000-0002-7541-9565
Wetzel, Andrew0000-0003-0603-8942
Ma, Xiangcheng0000-0001-8091-2349
Moreno, Jorge0000-0002-3430-3232
Hafen, Zachary0000-0001-7326-1736
Gurvich, Alexander B.0000-0002-6145-3674
Hopkins, Philip F.0000-0003-3729-1684
Kereš, Dušan0000-0002-1666-7067
Faucher-Giguère, Claude-André0000-0002-4900-6628
Feldmann, Robert0000-0002-1109-1919
Quataert, Eliot0000-0001-9185-5044
Additional Information:© 2021 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2021 May 4. Received 2021 April 22; in original form 2021 March 5. Published: 13 May 2021. SY and JSB were supported by NSF grants AST-1910346 and AST-1518291. CK was supported by a National Science Foundation Graduate Research Fellowship Program under grant DGE-1839285. JS is supported also by the German Science Foundation via DIP grant STE 1869/2-1 GE 625/17-1. AW received support from NASA through ATP grants 80NSSC18K1097 and 80NSSC20K0513; HST grants GO-14734, AR-15057, AR-15809, and GO-15902 from STScI; a Scialog Award from the Heising-Simons Foundation; and a Hellman Fellowship. Support for JM is provided by the NSF (AST Award Number 1516374). ZH was supported by a Gary A. McCue postdoctoral fellowship at UC Irvine. ABG was supported by an NSFGRFP under grant DGE-1842165 and was additionally supported by NSF grants DGE-0948017 and DGE-145000. Support for PFH was provided by NSF Research Grants 1911233 and 20009234, NSF CAREER grant 1455342, NASA grants 80NSSC18K0562, HST-AR-15800.001-A. Numerical calculations were run on the Caltech compute cluster ‘Wheeler,’ allocations FTA-Hopkins/AST20016 supported by the NSF and TACC, and NASA HEC SMD-16-7592. CAFG was supported by NSF through grants AST-1715216 and CAREER award AST-1652522; by NASA through grant 17-ATP17-0067; by STScI through grant HST-AR-16124.001-A; and by a Cottrell Scholar Award and a Scialog Award from the Research Corporation for Science Advancement. RF acknowledges financial support from the Swiss National Science Foundation (grant nos 157591 and 194814). We ran simulations using: XSEDE, supported by NSF grant ACI-1548562; Blue Waters, supported by the NSF; Pleiades, via the NASA HEC program through the NAS Division at Ames Research Center. Data Availability: The data supporting the plots within this article are available on reasonable request to the corresponding author. A public version of the GIZMO code is available at Additional data including simulation snapshots, initial conditions, and derived data products are available at Some of the publicly available software packages used to analyse these data are available at and
Group:Astronomy Department, TAPIR
Funding AgencyGrant Number
NSF Graduate Research FellowshipDGE-1839285
Deutsche Forschungsgemeinschaft (DFG)STE 1869/2-1 GE 625/17-1
NASA Hubble FellowshipGO-14734
NASA Hubble FellowshipAR-15057
NASA Hubble FellowshipAR-15809
NASA Hubble FellowshipGO-15902
Heising-Simons FoundationUNSPECIFIED
Hellman FellowshipUNSPECIFIED
University of California, IrvineUNSPECIFIED
NSF Graduate Research FellowshipDGE-1842165
NSF Graduate Research FellowshipDGE-0948017
NSF Graduate Research FellowshipDGE-145000
Cottrell Scholar of Research CorporationUNSPECIFIED
Swiss National Science Foundation (SNSF)157591
Swiss National Science Foundation (SNSF)194814
Subject Keywords:methods: numerical –Galaxy: disc – galaxies: formation – galaxies: evolution – galaxies: star formation
Issue or Number:1
Record Number:CaltechAUTHORS:20210803-200634030
Persistent URL:
Official Citation:Sijie Yu, James S Bullock, Courtney Klein, Jonathan Stern, Andrew Wetzel, Xiangcheng Ma, Jorge Moreno, Zachary Hafen, Alexander B Gurvich, Philip F Hopkins, Dušan Kereš, Claude-André Faucher-Giguère, Robert Feldmann, Eliot Quataert, The bursty origin of the Milky Way thick disc, Monthly Notices of the Royal Astronomical Society, Volume 505, Issue 1, July 2021, Pages 889–902,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:110139
Deposited By: Tony Diaz
Deposited On:04 Aug 2021 19:03
Last Modified:04 Aug 2021 19:03

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