The formation times and building blocks of Milky Way-mass galaxies in the FIRE simulations
Abstract
Surveys of the Milky Way (MW) and M31 enable detailed studies of stellar populations across ages and metallicities, with the goal of reconstructing formation histories across cosmic time. These surveys motivate key questions for galactic archaeology in a cosmological context: When did the main progenitor of an MW/M31-mass galaxy form, and what were the galactic building blocks that formed it? We investigate the formation times and progenitor galaxies of MW/M31-mass galaxies using the Feedback In Realistic Environments-2 cosmological simulations, including six isolated MW/M31-mass galaxies and six galaxies in Local Group (LG)-like pairs at z = 0. We examine main progenitor 'formation' based on two metrics: (1) transition from primarily ex-situ to in-situ stellar mass growth and (2) mass dominance compared to other progenitors. We find that the main progenitor of an MW/M31-mass galaxy emerged typically at z ∼ 3–4 (11.6−12.2 Gyr ago), while stars in the bulge region (inner 2 kpc) at z = 0 formed primarily in a single main progenitor at z ≲ 5 ≾ 12.6 Gyr ago). Compared with isolated hosts, the main progenitors of LG-like paired hosts emerged significantly earlier (Δz ∼ 2, Δt ~ 1.6 Gyr), with ∼4× higher stellar mass at all z ≳ 4 ≳ 12.2 Gyr ago). This highlights the importance of environment in MW/M31-mass galaxy formation, especially at early times. On average, about 100 galaxies with Mₛₜₐᵣ ≳ 10⁵ M_⊙ went into building a typical MW/M31-mass system. Thus, surviving satellites represent a highly incomplete census (by ∼5×) of the progenitor population.
Additional Information
© 2020 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). The authors thank the anonymous referee for their helpful and thorough report. IBS, AW, and SB received support from NASA, through ATP grant 80NSSC18K1097 and HST grants GO-14734 and AR-15057 from STScI, the Heising-Simons Foundation, and a Hellman Fellowship. JBH acknowledges support from an ARC Laureate Fellowship. MBK acknowledges support from NSF grants AST-1517226, AST-1910346, and CAREER grant AST-1752913 and from NASA grants NNX17AG29G and HST-AR-14282, HST-AR-14554, HST-AR-15006, HST-GO-14191, and HST-GO-15658 from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555. CAFG was supported by NSF through grants AST-1517491, AST-1715216, and CAREER award AST-1652522; by NASA through grant 17-ATP17-0067; and by a Cottrell Scholar Award from the Research Corporation for Science Advancement. We ran and analysed simulations using XSEDE supported by NSF grant ACI-1548562, Blue Waters via allocation PRAC NSF.1713353 supported by the NSF, and NASA HEC Program through the NAS Division at Ames Research Center. Some of this work was performed in part at KITP, supported by NSF grant PHY-1748958. This work also used various python packages including numpy (van der Walt, Colbert & Varoquaux 2011), scipy (Virtanen et al. 2020), and matplotlib (Hunter 2007), as well as NASA's Astrophysics Data System. DATA AVAILABILITY. Full simulation snapshots at z = 0 are available for m12i, m12f, and m12m at ananke.hub.yt. The python code used to analyse these data is available at https://bitbucket.org/isantis/progenitor, which uses the publicly available packages https://bitbucket.org/awetzel/gizmo_analysis, https://bitbucket.org/awetzel/halo_analysis, and https://bitbucket.org/awetzel/utilities. Finally, data values in each figures are available at https://ibsantistevan.wixsite.com/mysite/publications.Additional details
- Eprint ID
- 118704
- Resolver ID
- CaltechAUTHORS:20230105-894416000.25
- NASA
- 80NSSC18K1097
- NASA
- HST-GO-14734
- NASA
- HST-AR-15057
- Heising-Simons Foundation
- Hellman Fellowship
- Australian Research Council
- NSF
- AST-1517226
- NSF
- AST-1910346
- NSF
- AST-1752913
- NASA
- NNX17AG29G
- NASA
- HST-AR-14282
- NASA
- HST-AR-14554
- NASA
- HST-AR-15006
- NASA
- HST-GO-14191
- NASA
- HST-GO-15658
- NASA
- NAS5-26555
- NSF
- AST-1517491
- NSF
- AST-1715216
- NSF
- AST-1652522
- NASA
- 17-ATP17-0067
- Cottrell Scholar of Research Corporation
- NSF
- ACI-1548562
- NSF
- OAC-1713353
- NSF
- PHY-1748958
- Created
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2023-01-18Created from EPrint's datestamp field
- Updated
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2023-01-18Created from EPrint's last_modified field