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Published January 2024 | Version Published
Journal Article Open

Disc settling and dynamical heating: histories of Milky Way-mass stellar discs across cosmic time in the FIRE simulations

Creators

  • 1. ROR icon University of California, Berkeley
  • 2. ROR icon University of California, Merced
  • 3. ROR icon Pomona College
  • 4. ROR icon Northwestern University
  • 5. ROR icon California Institute of Technology

Abstract

We study the kinematics of stars both at their formation and today within 14 Milky Way (MW)-mass galaxies from the FIRE-2 cosmological zoom-in simulations. We quantify the relative importance of cosmological disc settling and post-formation dynamical heating. We identify three eras: a Pre-Disc Era (typically ≳ 8 Gyr ago), when stars formed on dispersion-dominated orbits; an Early-Disc Era (≈8–4 Gyr ago), when stars started to form on rotation-dominated orbits but with high velocity dispersion, σform; and a Late-Disc Era (≲ 4 Gyr ago), when stars formed with low σform. σform increased with time during the Pre-Disc Era, peaking ≈8 Gyr ago, then decreased throughout the Early-Disc Era as the disc settled and remained low throughout the Late-Disc Era. By contrast, the dispersion measured today, σnow, increases monotonically with age because of stronger post-formation heating for Pre-Disc stars. Importantly, most of σnow was in place at formation, not added post-formation, for stars younger than ≈10 Gyr. We compare the evolution of the three velocity components: at all times, σR, form > σϕ, form > σZ, form. Post-formation heating primarily increased σR at ages ≲ 4 Gyr but acted nearly isotropically for older stars. The kinematics of young stars in FIRE-2 broadly agree with the range observed across the MW, M31, M33, and PHANGS-MUSE galaxies. The lookback time that the disc began to settle correlates with its dynamical state today: earlier-settling galaxies currently form colder discs. Including stellar cosmic-ray feedback does not significantly change disc rotational support at fixed stellar mass.

Copyright and License

© The Author(s) 2023. Published by Oxford University Press on behalf of 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.

Acknowledgement

We thank Jonathan Stern for helpful comments and the participants of the Disk Formation Workshop at UC Irvine for their enlightening discussions. FM and AW received support from: NSF via CAREER award AST-2045928 and grant AST-2107772; NASA ATP grant 80NSSC20K0513; HST grants AR-15809, GO-15902, GO-16273 from STScI; and a Scialog Award from the Heising-Simons Foundation. CAFG was supported by NSF through grants AST-2108230 and CAREER award AST-1652522; by NASA through grants 17-ATP17-0067 and 21-ATP21-0036; by STScI through grant HST-GO-16730.016-A; by CXO through grant TM2-23005X; and by the Research Corporation for Science Advancement through a Cottrell Scholar Award. PFH recieved supported by NSF Research Grants 1911233 and 20009234, NSF CAREER grant 1455342, and NASA grants 80NSSC18K0562 and HST-AR-15800.001-A. We performed some of this work at the Aspen Center for Physics, supported by NSF grant PHY-1607611. We ran simulations using: XSEDE, supported by NSF grant ACI-1548562; Blue Waters, supported by the NSF; Frontera allocations AST21010 and AST20016, supported by the NSF and TACC; Pleiades, via the NASA HEC program through the NAS Division at Ames Research Center.

Data Availability

All of the python code that we used to generate these figures are available at https://fmccluskey.github.io, which uses the publicly available package https://bitbucket.org/awetzel/gizmo_analysis (Wetzel & Garrison-Kimmel 2020). The FIRE-2 simulations are publicly available (Wetzel et al. 2023) at http://flathub.flatironinstitute.org/fire. Additional FIRE simulation data is available at https://fire.northwestern.edu/data. A public version of the gizmo code is available at http://www.tapir.caltech.edu/~phopkins/Site/GIZMO.html.

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Additional details

Related works

Is new version of
Discussion Paper: arXiv:2303.14210 (arXiv)

Funding

National Science Foundation
AST-2045928
National Science Foundation
AST-2107772
National Aeronautics and Space Administration
80NSSC20K0513
National Aeronautics and Space Administration
AR-15809
National Aeronautics and Space Administration
GO-15902
National Aeronautics and Space Administration
GO-16273
Heising-Simons Foundation
Scialog Award -
National Science Foundation
AST-2108230
National Science Foundation
AST-1652522
National Aeronautics and Space Administration
17-ATP17-0067
National Aeronautics and Space Administration
21-ATP21-0036
Space Telescope Science Institute
HST-GO-16730.016-A
Space Telescope Science Institute
TM2-23005X
Research Corporation for Science Advancement
Cottrell Scholar Award -
National Science Foundation
1911233
National Science Foundation
20009234
National Science Foundation
1455342
National Aeronautics and Space Administration
80NSSC18K0562
National Aeronautics and Space Administration
HST-AR-15800.001-A
National Science Foundation
PHY-1607611
National Science Foundation
ACI-1548562
National Science Foundation
AST21010
National Science Foundation
AST20016

Dates

Submitted
2023-03-28
Accepted
2023-10-27
Available
2023-12-06
Published
Available
2023-12-08
Corrected and typeset

Caltech Custom Metadata

Caltech groups
Astronomy Department, TAPIR, Walter Burke Institute for Theoretical Physics, Division of Physics, Mathematics and Astronomy (PMA)
Publication Status
Published