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Rapid disc settling and the transition from bursty to steady star formation in Milky Way-mass galaxies

Gurvich, Alexander B. and Stern, Jonathan and Faucher-Giguère, Claude-André and Hopkins, Philip F. and Wetzel, Andrew and Moreno, Jorge and Hayward, Christopher C. and Richings, Alexander J. and Hafen, Zachary (2022) Rapid disc settling and the transition from bursty to steady star formation in Milky Way-mass galaxies. . (Unpublished)

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Recent observations and simulations indicate substantial evolution in the properties of galaxies with time, wherein rotationally-supported and steady thin discs (like those frequently observed in the local universe) emerge from galaxies that are clumpy, irregular, and have bursty star formation rates (SFRs). To better understand the progenitors of local disc galaxies we carry out an analysis of three FIRE-2 simulated galaxies with a mass similar to the Milky Way at redshift z=0. We show that all three galaxies transition from bursty to steady SFRs at a redshift between z=0.5 and z=0.8, and that this transition coincides with a rapid (< ~1 Gyr) emergence of a rotationally-supported interstellar medium (ISM).In the late phase with steady SFR, the rotational energy comprises > ~90% of the total kinetic + thermal energy in the ISM, and is roughly half the gravitational energy. By contrast, during the early phase with bursty star formation, the ISM has a quasi-spheroidal morphology and its energy budget is dominated by quasi-isotropic flows including turbulence and coherent inflows/outflows. This result, that rotational support is subdominant at early times, challenges the common application of equilibrium disc models to the high-redshift progenitors of Milky Way-like galaxies. We further find that the formation of a rotation-supported ISM coincides with the formation of a thermal energy-supported inner circumgalactic medium (CGM). Before this transition, the inner CGM is also supported by turbulence and coherent flows, indicating that at early times there is no clear boundary between the ISM and inner CGM.

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper ItemGIZMO code ItemFIRE-2 simulations ItemAdditional data including simulation snapshots, initial conditions, and derived data products ItemJournal Article
Gurvich, Alexander B.0000-0002-6145-3674
Stern, Jonathan0000-0002-7541-9565
Faucher-Giguère, Claude-André0000-0002-4900-6628
Hopkins, Philip F.0000-0003-3729-1684
Wetzel, Andrew0000-0003-0603-8942
Moreno, Jorge0000-0002-3430-3232
Hayward, Christopher C.0000-0003-4073-3236
Richings, Alexander J.0000-0003-0502-9235
Hafen, Zachary0000-0001-7326-1736
Additional Information:We thank Vasily Belokurov and Andrey Kravtsov for sharing an advance copy of their paper on the identification of the Aurora stellar component and its interpretation in terms of an early chaotic phase in the Milky Way’s evolution. ABG was supported by an NSF-GRFP under grant DGE-1842165 and was additionally supported by NSF grants DGE-0948017 and DGE-145000. JS was supported by the Israel Science Foundation (grant No. 2584/21) and by the German Science Foundation via DIP grant STE 1869/2-1 GE625/17-1. CAFG was supported by NSF through grants AST-1715216, AST-2108230, and CAREER award AST-1652522; by NASA through grant 17-ATP17-0067; by STScI through grant HST-AR-16124.001-A; and by the Research Corporation for Science Advancement through a Cottrell Scholar Award. Support for PFH was provided by NSF Research Grants 1911233 & 20009234, NSF CAREER grant 1455342, NASA grants 80NSSC18K0562, HST-AR-15800.001-A. AW received support from: NSF grants CAREER 2045928 and 2107772; NASA ATP grants 80NSSC18K1097 and 80NSSC20K0513; HST grants AR-15809 and GO-15902 from STScI; a Scialog Award from the Heising-Simons Foundation; and a Hellman Fellowship. AJR was supported by a COFUND/Durham Junior Research Fellowship under EU grant 609412; and by the Science and Technology Facilities Council [ST/T000244/1]. Numerical calculations were run on the Caltech computer cluster Wheeler, the Northwestern computer cluster Quest, Frontera allocation FTA-Hopkins/AST20016 supported by the NSF and TACC, XSEDE allocations ACI-1548562, TG-AST140023, and TG-AST140064, and NASA HEC allocations SMD-16-7561, SMD-17-1204, and SMD-16-7592. ZH was supported by a Gary A. McCue postdoctoral fellowship at UC Irvine. The data used in this work were, in part, hosted on facilities supported by the Scientific Computing Core at the Flatiron Institute, a division of the Simons Foundation. 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 FIRE-2 simulations are publicly available (Wetzel et al. 2022) at Additional data including simulation snapshots, initial conditions, and derived data products are available at
Group:Astronomy Department, TAPIR
Funding AgencyGrant Number
NSF Graduate Research FellowshipDGE-1842165
NSF Graduate Research FellowshipDGE-0948017
NSF Graduate Research FellowshipDGE-1450006
Israel Science Foundation2584/21
Deutsche Forschungsgemeinschaft (DFG)STE 1869/2-1 GE 625/17-1
Cottrell Scholar of Research CorporationUNSPECIFIED
Heising-Simons FoundationScialog Award
Hellman FellowshipUNSPECIFIED
European Research Council (ERC)609412
Science and Technology Facilities Council (STFC)ST/T000244/1
Texas Advanced Computing Center (TACC)UNSPECIFIED
University of California, IrvineUNSPECIFIED
Simons FoundationUNSPECIFIED
Subject Keywords:galaxies: formation – galaxies: evolution – galaxies: disc – galaxies: star formation – galaxies: ISM
Record Number:CaltechAUTHORS:20220816-222038999
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:116340
Deposited By: George Porter
Deposited On:17 Aug 2022 16:37
Last Modified:29 Mar 2023 23:34

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