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Rapid disc settling and the transition from bursty to steady star formation in Milky Way-mass galaxies
Astrophysics of Galaxies · Submitted 8 Mar 2022
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim 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.
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The abstract, sentence by sentence
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.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | 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). | background 1.00 | 0.05 | 0.11 | hedged possibility 0.97 |
| s1 | 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. | contribution 0.65 | 0.95 | 0.03 | asserted 0.80 |
| s2 | 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. | result 1.00 | 0.96 | 0.72 | asserted 1.00 |
| s3 | 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. | result 1.00 | 0.87 | 0.10 | asserted 1.00 |
| s4 | 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. | interpretation 1.00 | 0.55 | 0.30 | asserted 0.99 |
| s5 | We further find that the formation of a rotation-supported ISM coincides with the formation of a thermal energy-supported inner circumgalactic medium (CGM). | result 1.00 | 0.95 | 0.11 | asserted 1.00 |
| s6 | 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. | result 0.95 | 0.91 | 0.06 | asserted 0.92 |
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The paper
Original abstract
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.
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References
How later papers used it
66 later papers cite it
1 paper by the same authors is listed below: 1 used its method or tool.
Uses its method or tool 1 of 5 papers with this label · 1 by the same authors
By the same authors
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Following [ref] , we define the galaxy's rotation axis as the total angular momentum of all star particles within $5 R_s,1/2$, where $R_s,1/2$ is the radius that encloses 50% of the total stellar mass contained within $0.2 R_vir$.
Cold vs. Hot Gas Accretion and Angular Momentum in FIRE Simulations: From Halo to Galaxy Scales (2026) (same authors) · Galaxy centering · 1.00
How the literature uses it
26 arXiv papers cite this in 63 sentences
Papers citing it · 50 sentences without a confident label
Builds on it 1 paper
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It extends work from a series of FIRE-2 papers that have examined the relationship between star formation burstiness, galaxy kinematics, galaxy morphology, metallicity gradients, and the development of a hot gaseous halos around galaxies [ref] .
Born this way: thin disc, thick disc, and isotropic spheroid formation in FIRE-2 Milky-Way-mass galaxy simulations · Introduction · 0.95
Uses its method or tool 2 papers
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Therefore we do not attempt to “optimize” $$ but rather for each simulation we determine it following the method used in [ref] .
Stellar feedback-regulated black hole growth: driving factors from nuclear to halo scales · Comparing the Time of Accelerated BH Growth with Thresholds in Other Physical Properties · 1.00
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[ref] uses the running scatter in the SFH in 300 Myr windows, $σ_300 Myr(log(SFR))$, to quantify the fluctuations and define $t_B$ as the time after which this quantity remains below 0.3 dex.
Born this way: thin disc, thick disc, and isotropic spheroid formation in FIRE-2 Milky-Way-mass galaxy simulations · Definitions · 0.98
Cites it as support 5 papers
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[ref] and [ref] showed that the transition from bursty to steady star formation coincides with the rapid “settling” of the ISM into a steady, thin disc in the simulations.
Stellar feedback-regulated black hole growth: driving factors from nuclear to halo scales · Connection to the Settling of Galactic Discs · 0.96
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For satellites in category (1), a time-dependent and/or triaxial host halo potential likely plays an important role, especially given that satellites with growing pericenters typically fell in early, when the shape of the host halo potential was changing more rapidly [ref] .
Orbital dynamics and histories of satellite galaxies around Milky Way-mass galaxies in the FIRE simulations · Satellites with growing pericenters · 0.96
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Because we have defined our GCs as those clusters older than 6 Gyr, they are preferentially formed on isotropically distributed orbits [ref] , while the younger clusters are preferentially formed within the disk [ref] .
Great Balls of FIRE II: The evolution and destruction of star clusters across cosmic time in a Milky Way-mass galaxy · Ages, Metallicities, and Galactic Positions · 0.96
Cites it as background 4 papers
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Over the past decade, galaxy formation simulations have been useful for investigating disk formation [ref] .
Formation of Galactic Disks I: Why Did the Milky Way's Disk Form Unusually Early? · Introduction · 0.98
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The transition from bursty to more steady star formation in FIRE simulations, including the connection to galactic outflows, has been studied in a number of recent papers (e.g., [ref] , [ref] ).
The inefficiency of stellar feedback in driving galactic outflows in massive galaxies at high redshift · Main properties of the simulated galaxies · 1.00
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On the other hand, fully cosmological simulations can provide insights into the nature of cosmic accretion [ref] , the contribution of satellites to the cool CGM reservoir [ref] , and how the conditions of the CGM affect the formation of galactic structure [ref] .
A unified model for the co-evolution of galaxies and their circumgalactic medium: the relative roles of turbulence and atomic cooling physics · Introduction · 0.81
What it cites · 12 sentences without a confident label
Compares with 1 paper
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Comparing their results with a set of simulations of Milky Way-mass galaxies, including publicly-available FIRE-2 simulations [ref] , they deduce a rapid disc formation time scale of $≈1-2$ Gyr, similar to what our simulations predict, though the Milky Way disc appears to form earlier and at lower metallicity than in the three simulations analysed in this paper.
Public data release of the FIRE-2 cosmological zoom-in simulations of galaxy formation · When and where do we expect discs? · 0.93
Cites as background 3 papers
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Previous studies based on idealized models and arguments suggested that a qualitative change in stellar feedback-driven outflows is expected when the disc crosses a threshold in the depth of its gravitational potential well [ref] , in its gas fraction [ref] , in its dynamical time [ref] , or in its star formation rate surface density [ref] .
Bursty star formation during the Cosmic Dawn driven by delayed stellar feedback · What are the mechanisms that drive disc settling? · 0.97
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There is also a third possibility, recently suggested by [ref] and followed up by [ref] and [ref] , in which observed SFG trends are driven by a change in the physics of gas surrounding the galaxy, known as the circumgalactic medium (CGM).
The bursty origin of the Milky Way thick disc · Introduction · 0.93
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There is also a third possibility, recently suggested by [ref] and followed up by [ref] and [ref] , in which observed SFG trends are driven by a change in the physics of gas surrounding the galaxy, known as the circumgalactic medium (CGM).
Hot-mode accretion and the physics of thin-disk galaxy formation · Introduction · 0.93
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