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arxiv: 2508.21126 · v2 · submitted 2025-08-28 · 🌌 astro-ph.GA · astro-ph.CO

The COLIBRE project: cosmological hydrodynamical simulations of galaxy formation and evolution

Joop Schaye , Evgenii Chaikin , Matthieu Schaller , Sylvia Ploeckinger , Filip Hu\v{s}ko , Rob McGibbon , James W. Trayford , Alejandro Ben\'itez-Llambay
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Camila Correa Carlos S. Frenk Alexander J. Richings Victor J. Forouhar Moreno Yannick M. Bah\'e Josh Borrow Anna Durrant Andrea Gebek John C. Helly Adrian Jenkins Cedric G. Lacey Aaron Ludlow Folkert S. J. Nobels
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Pith reviewed 2026-05-18 20:18 UTC · model grok-4.3

classification 🌌 astro-ph.GA astro-ph.CO
keywords galaxy formationcosmological simulationshydrodynamical simulationssubgrid feedbackAGN feedbackstellar mass functionnumerical convergenceinterstellar medium
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The pith

The COLIBRE simulations reproduce key low-redshift galaxy observations after calibrating subgrid feedback to stellar mass functions, sizes, and black hole masses.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This paper presents the COLIBRE galaxy formation model and a suite of large cosmological hydrodynamical simulations. The model incorporates explicit treatments of multiphase gas, non-equilibrium chemistry, dust grains, and multiple feedback channels from stars and black holes without using a pressure floor. Feedback parameters are adjusted so that the simulated galaxies match the observed present-day stellar mass function, galaxy sizes, and black hole masses in massive systems. Once calibrated this way, the runs display good numerical convergence across resolutions and match a variety of other low-redshift galaxy data.

Core claim

The COLIBRE project introduces new subgrid models for radiative cooling, dust, star formation, stellar mass loss, turbulent diffusion, supernova feedback, and AGN feedback within cosmological hydrodynamical simulations. After tuning the feedback parameters exclusively to the observed z ≈ 0 galaxy stellar mass function, galaxy sizes, and black hole masses in massive galaxies, the simulations achieve very good numerical convergence and excellent agreement with multiple low-redshift galaxy observations. The largest runs contain 136 billion particles in volumes up to 400 comoving megaparsecs on a side.

What carries the argument

The subgrid feedback model calibrated to match the z ≈ 0 galaxy stellar mass function, galaxy sizes, and black hole masses in massive galaxies.

If this is right

  • The simulations match observed galaxy sizes and black hole masses in massive systems at the present day.
  • Numerical convergence holds across particle masses from 10^5 to 10^7 solar masses.
  • A subset of runs with spin-dependent hybrid jet and thermal AGN feedback explores additional black-hole effects.
  • The explicit multiphase ISM treatment without a pressure floor allows direct comparison with observed gas properties.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same calibration strategy could be tested against the evolution of the stellar mass function with redshift to check whether low-redshift tuning captures earlier galaxy growth.
  • Tracking multiple dust grain species and sizes may improve predictions for metal-line cooling and extinction that were not part of the calibration.
  • Supersampling dark matter particles by a factor of four reduces spurious energy transfer and could be adopted in other large-volume simulations to improve baryonic dynamics.
  • The hybrid AGN feedback runs offer a way to examine how black-hole spin affects galaxy quenching without changing the overall calibration.

Load-bearing premise

Tuning the subgrid feedback parameters exclusively to present-day galaxy observations produces predictions that remain reliable at higher redshifts and for quantities not used in the calibration.

What would settle it

A clear mismatch between the simulated and observed galaxy stellar mass function or size distribution at redshift greater than 1 would show that the low-redshift calibration does not generalize.

read the original abstract

We present the COLIBRE galaxy formation model and the COLIBRE suite of cosmological hydrodynamical simulations. COLIBRE includes new models for radiative cooling, dust grains, star formation, stellar mass loss, turbulent diffusion, pre-supernova stellar feedback, supernova feedback, supermassive black holes and active galactic nucleus (AGN) feedback. The multiphase interstellar medium is explicitly modelled without a pressure floor. Hydrogen and helium are tracked in non-equilibrium, with their contributions to the free electron density included in metal-line cooling calculations. The chemical network is coupled to a dust model that tracks three grain species and two grain sizes. In addition to the fiducial thermally-driven AGN feedback, a subset of simulations uses black hole spin-dependent hybrid jet/thermal AGN feedback. To suppress spurious transfer of energy from dark matter to stars, dark matter is supersampled by a factor 4, yielding similar dark matter and baryonic particle masses. The subgrid feedback model is calibrated to match the observed $z \approx 0$ galaxy stellar mass function, galaxy sizes, and black hole masses in massive galaxies. The COLIBRE suite includes three resolutions, with particle masses of $\sim 10^5$, $10^6$, and $10^7\,\text{M}_\odot$ in cubic volumes of up to 100, 200, and 400 cMpc on a side, respectively. The largest runs use 136 billion ($5 \times 3008^3$) particles. We describe the model, assess its strengths and limitations, and present both visual impressions and quantitative results. Comparisons with various low-redshift galaxy observations generally show very good numerical convergence and excellent agreement with the data.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 0 minor

Summary. The manuscript presents the COLIBRE galaxy formation model and associated suite of cosmological hydrodynamical simulations. It incorporates new subgrid physics including non-equilibrium H/He chemistry, a three-species dust model with two grain sizes, turbulent diffusion, pre-supernova and supernova feedback, and both thermal and spin-dependent hybrid jet/thermal AGN feedback. Dark matter is supersampled by a factor of four. The subgrid feedback parameters are calibrated to the observed z≈0 galaxy stellar mass function, galaxy sizes, and black hole masses in massive galaxies. The suite spans three resolutions (particle masses ~10^5 to 10^7 M_⊙) in volumes up to 400 cMpc, with the largest runs using 136 billion particles. The paper reports very good numerical convergence and excellent agreement with a range of low-redshift galaxy observations.

Significance. The work introduces a simulation framework with explicit multiphase ISM modeling and hybrid AGN feedback, run in large volumes at multiple resolutions. The reported numerical convergence across resolutions and the scale of the simulations are clear strengths. If the model demonstrates agreement with observables independent of the calibration set, it would offer a useful calibrated tool for studying galaxy populations at low redshift.

major comments (2)
  1. Abstract: the claim of 'excellent agreement with the data' after calibration to the z≈0 stellar mass function, galaxy sizes, and black hole masses in massive galaxies requires explicit separation of calibration targets from validation observables; without this distinction the agreement with the calibrated quantities is expected by construction rather than an independent test of the model.
  2. Section describing the calibration procedure: the manuscript should quantify how many of the 'various low-redshift galaxy observations' shown in the comparisons are independent of the three calibration targets, and report the level of agreement for those independent quantities separately.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their constructive comments and positive overall assessment of the COLIBRE simulations. We agree that clearly separating the calibration targets from independent validation observables strengthens the manuscript and better highlights the model's predictive capabilities. We have revised the abstract and the calibration section accordingly.

read point-by-point responses

  1. Referee: Abstract: the claim of 'excellent agreement with the data' after calibration to the z≈0 stellar mass function, galaxy sizes, and black hole masses in massive galaxies requires explicit separation of calibration targets from validation observables; without this distinction the agreement with the calibrated quantities is expected by construction rather than an independent test of the model.

    Authors: We agree that this distinction is important for clarity. In the revised manuscript we have updated the abstract to explicitly state that the subgrid model is calibrated to the z≈0 stellar mass function, galaxy sizes, and black hole masses in massive galaxies, and that the reported 'excellent agreement' with these quantities is by construction. We now note that comparisons with additional low-redshift observables (e.g., star-formation rates, gas fractions, and metallicity relations) serve as independent validation tests of the model. revision: yes

  2. Referee: Section describing the calibration procedure: the manuscript should quantify how many of the 'various low-redshift galaxy observations' shown in the comparisons are independent of the three calibration targets, and report the level of agreement for those independent quantities separately.

    Authors: We accept this recommendation. We have added a dedicated paragraph in the calibration section that enumerates the full set of low-redshift comparisons presented in the paper. Of these, we now explicitly identify which are independent of the three calibration targets and provide separate quantitative summaries of agreement (e.g., median offsets and scatter relative to observational data) for the independent subset. This makes the predictive success of the model on uncalibrated properties transparent. revision: yes

Circularity Check

0 steps flagged

No significant circularity

full rationale

The paper explicitly describes calibrating the subgrid feedback parameters to match three specific z≈0 observables (stellar mass function, galaxy sizes, black-hole masses in massive galaxies) and then reports that comparisons with various other low-redshift galaxy observations show good numerical convergence and agreement. Because the calibration targets are stated separately from the broader comparison set, and because the central results are benchmarked directly against external observational data rather than derived from self-referential equations or self-citations, no load-bearing step reduces to its own inputs by construction. The work is therefore self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

1 free parameters · 2 axioms · 0 invented entities

The central results rest on a small number of calibrated subgrid parameters plus standard assumptions of cosmological hydrodynamics; no new fundamental entities are postulated.

free parameters (1)
  • subgrid feedback efficiencies and coupling strengths
    Calibrated by hand to reproduce the observed z≈0 galaxy stellar mass function, galaxy sizes, and black hole masses in massive galaxies.
axioms (2)
  • domain assumption Lambda-CDM background cosmology and initial conditions
    Standard assumption invoked for all cosmological volume simulations.
  • domain assumption Validity of subgrid approximations for unresolved interstellar medium and feedback physics
    Required to run the simulations at the stated resolutions.

pith-pipeline@v0.9.0 · 5954 in / 1410 out tokens · 49560 ms · 2026-05-18T20:18:12.738356+00:00 · methodology

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Forward citations

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  4. The galaxy ultraviolet luminosity function from $z=7$ to $15$ in the COLIBRE simulations

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  6. Galaxy Populations in the IllustrisTNG Caustic Skeleton

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    Disc galaxies inhibit supermassive black hole growth by preserving rotational support in central gas, while mergers in ellipticals disrupt this support and enable rapid accretion.

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  9. Towards Reconciling Reionization with JWST: The Role of Bright Galaxies and Strong Feedback

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    Strong-feedback models with bright galaxies match JWST UVLF at z greater than or equal to 10 and predict an extended reionization from z approximately 16 to 6 that fits CMB optical depth within 2 sigma.

  10. Two-phase formation of galaxies: the coevolution between galaxies and dark matter halos

    astro-ph.GA 2025-09 unverdicted novelty 5.0

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  11. The evolution of the galaxy stellar mass function and star formation rates in the COLIBRE simulations from redshift 17 to 0

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    COLIBRE simulations match observed galaxy stellar mass functions, star formation rates, and quenched fractions from z=17 to z=0, including JWST massive quiescent galaxies at high redshift.

  12. COLIBRE: calibrating subgrid feedback in cosmological simulations that include a cold gas phase

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