arXiv subjects

James W. Trayford

Publications and source records attributed to James W. Trayford.

At least 19 recordsLinked to original sources

arXiv2026

Galaxy luminosity functions from far-UV to submillimetre at $z=0$ in the COLIBRE simulations

We present predictions from the COLIBRE cosmological hydrodynamical simulations of galaxy formation for the present-day galaxy luminosity functions (LFs) at wavelengths ranging from the far-ultraviolet (FUV) to the submillimetre. The simulations are post-processed with the radiative transfer code SKIRT, accounting for dust attenuation and emission using the distribution and properties of dust grains predicted directly by COLIBRE. Results from simulations varying in mass resolution by a factor of $\sim 10^2$ ($\sim 10^5 - 10^7\,\mathrm{M_{\odot}}$) show very good convergence over most luminosity ranges. The COLIBRE-SKIRT LFs match the data remarkably well from the FUV to $3.4\,μ\rm m$ and also in the far-infrared and submillimetre wavelength range ($70-850\,μ\rm m$). In the mid-infrared (MIR; $8-24\,μ\rm m$), COLIBRE-SKIRT matches the data well at low luminosities but significantly underpredicts the luminosities of MIR-bright galaxies, with the discrepancy increasing towards longer wavelengths. The total infrared LF, obtained by integrating the spectral energy distributions over $8-1000\,μ\rm m$, also matches observations well at the faint end but underpredicts the number of very bright galaxies. The unprecedented agreement at all other wavelengths indicates that COLIBRE, coupled with this calibration-free SKIRT post-processing framework, successfully predicts the properties of stellar populations at the present day and the amount and distribution of interstellar dust.

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arXiv2026

The galaxy ultraviolet luminosity function from $z=7$ to $20$ in the COLIBRE simulations

JWST has enabled the detection of galaxies in the earliest stages of cosmic history. We compare the ultraviolet luminosity functions (UVLFs) at redshifts $z=7-20$ predicted by a set of new cosmological hydrodynamical simulations, COLIBRE, with observations, including those from JWST. The UV luminosities of COLIBRE galaxies are derived using the radiative transfer code SKIRT, which tracks stellar emission and its processing through the multi-phase interstellar medium and dust distribution predicted by COLIBRE. We find that although COLIBRE is consistent with the observed evolution of the stellar mass function up to $z=12$, its dust-attenuated UVLFs fall systematically below the observations at the bright end: at the number density of $10^{-6}\,\mathrm{Mpc^{-3}\,mag^{-1}}$, the brightest galaxies are underluminous by $\approx 1\,\rm mag$ at $z=7$, increasing to $\approx 2.5\,\rm mag$ at $z=15$. Accounting for observational uncertainties brings the COLIBRE UVLFs closer to the observational data, but does not fully resolve the discrepancy. Ignoring dust attenuation allows COLIBRE to produce sufficiently bright galaxies at $7\lesssim z \lesssim 12$, but at $z=15$, COLIBRE still underpredicts the luminosities of the brightest galaxies, indicating the need for additional physical mechanisms to boost the UV luminosities at the earliest cosmic epochs, such as a ''top-heavy'' stellar initial mass function. We fit the COLIBRE UVLFs with Schechter functions and calculate the evolution of the best-fit parameters. We find that the galaxy number density decreases, the characteristic luminosity becomes fainter and the faint-end slope becomes steeper towards higher redshifts. The UV luminosity density decreases by a factor of several hundred from $z = 7$ to $z = 15$.

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arXiv2026

The atomic multiphase interstellar medium of galaxies in the COLIBRE simulations

We analyse the neutral ISM of galaxies at redshift z=0 in the COLIBRE hydrodynamical simulations and investigate the conditions under which these two gas phases coexist in a narrow range of thermal pressures. COLIBRE galaxies are selected based on the metallicity of their ISM. The median and mass-weighted distributions of thermal pressures of the multiphase ISM are analysed and compared to thermal equilibrium models and observations. The ISM in galaxies with gas metallicities similar to solar values exhibits a clear multiphase structure with a warm and cold phase coexisting in a certain range of thermal pressures. The pressures at which the ISM is multiphase depend on the gas metallicity. For COLIBRE galaxies with lower metallicities ($Z_{\mathrm{ISM}}\lesssim0.1\,\mathrm{Z}_{\odot}$), this multiphase structure largely disappears, partly due to resolution. The thermal pressures weighted by the HI mass of the neutral phases in COLIBRE galaxies are lower than, but still comparable to, some theoretical works and observational estimates. The thermal pressures show a strong dependence on the weighting scheme. If weighted by the star formation rate or CI mass, the thermal pressures of the cold phase match those derived from observations. The resulting pressures depend on a combination of the assumed radiation field strength, dust abundance, limited resolution and the weighting scheme. The strong dependence of the thermal pressures on the weighting scheme indicates observational tracers used to estimate the thermal pressure are biased towards high-pressure regions.

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arXiv2026

Unveiling the population of massive quenched galaxies at $z\ge2$ in the COLIBRE simulations - II. The role of AGN feedback and environment on their emergence

Early ($z \gtrsim 2$) Massive ($M_{\star} \gtrsim 10^{10}\,\mathrm{M_{\odot}}$), Quenched Galaxies (MQGs) challenge current galaxy formation models. In this series, we study these systems using the new COLIBRE cosmological hydrodynamical simulations. Following the broad agreement between their predictions and observations found in the first paper, this second paper explores the processes driving galaxies to become massive and quenched in COLIBRE, identifying Active Galactic Nucleus (AGN) feedback as the primary quenching mechanism in both the thermal (L200m6 simulation) and hybrid (thermal+jet, L200m7h simulation) AGN feedback models implemented. However, the two models behave differently: while the thermal model efficiently quenches massive galaxies at $z>3$, the hybrid model is less effective because black holes (BHs) grow more slowly in the early Universe, and the jet component, which dominates the feedback energy, acts on longer timescales to impact galaxies. Both models predict quasar-like MQGs (AGN with $L_{\rm bol}\gtrsim10^{45}\,\mathrm{erg\,s^{-1}}$), with the most luminous systems associated with more recently quenched galaxies. Compared to star-forming galaxies of similar mass, MQGs host more massive BHs and exhibit higher star formation efficiencies. These differences arise primarily from their environments before quenching, particularly at local ($\rm 0.3\,cMpc$) to intermediate scales ($\rm 1.0\,cMpc$), where overdense regions are associated with enhanced gas inflows, higher BH accretion and, hence, feedback power. We find that about $54\%$ ($20\%$) of the $z=3$ MQGs survive as the main progenitors of $z=0$ galaxies, although up to $56\%$ ($60\%$) experience rejuvenation episodes at a given redshift $z<3$ in L200m6 (L200m7h). Our results highlight the central role of BH growth, AGN feedback and environment in driving rapid quenching in the early Universe.

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arXiv2026

Unveiling the population of massive quenched galaxies at $z\ge2$ in the COLIBRE simulations - I. Galaxy demographics

The James Webb Space Telescope has uncovered a substantial population of Massive ($M_{\star} > 10^{10}\,\mathrm{M_{\odot}}$), Quenched Galaxies (MQGs) in the early Universe ($z \ge 2$), whose properties challenge current galaxy formation models. In this series, we examine this population of MQGs within the new COLIBRE cosmological hydrodynamical simulations, which introduce key innovations in their sub-grid physics. In this first paper, we find a dependence of MQG number densities on both mass resolution and the Active Galactic Nucleus feedback implementation, as well as a significant impact from potential observational uncertainties. Using the fiducial $(200\,\rm cMpc)^3$ volume L200m6 simulation, which provides adequate volume, mass and spatial resolution to study these systems, we report number densities and stellar mass functions in broad agreement with the latest observations. The predicted quenching and formation timescales are qualitatively consistent with observational inferences, indicating extended formation (medians $t_{50}\approx0.5-1.5\,\mathrm{Gyr}$) followed by rapid quenching (medians $t_{\mathrm{q}}\lesssim0.6\,\mathrm{Gyr}$) with strong starburst episodes. Leveraging the state-of-the-art physics in COLIBRE, the model predicts that MQGs have dust and $\rm H_{2}$ fractions more than $1$~dex lower than their massive star-forming counterparts; generally consistent with the (scarce) observational estimates. MQGs and massive star-forming systems show broadly similar stellar sizes and kinematics, suggesting that size or morphological transformations occur after quenching in COLIBRE. Our results provide robust predictions for MQGs and show that tensions with observations are reduced when an effective observational uncertainty is forward-modelled.

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arXiv2026

Gravitational potential drives the concentration dependence of the stellar mass-halo mass relation

We investigate the origin of the scatter in the stellar mass-halo mass (SMHM) relation using the \colibre cosmological hydrodynamical simulations. At fixed halo mass, we find a clear positive correlation between stellar mass and halo concentration, particularly in low-mass haloes between $10^{11}$ and $10^{12}\,\rm M_\odot$, where all halo properties are computed from the corresponding dark-matter-only simulation. Two scenarios have been proposed to explain this trend: the earlier formation of higher-concentration haloes allows more time for star formation, or the deeper gravitational potential wells of higher-concentration haloes enhance baryon retention. To distinguish between them, we examine correlations between halo concentration, stellar mass, stellar age, and stellar metallicity. While, at fixed halo mass, halo concentration correlates with stellar age, stellar age itself shows only a weak correlation with stellar mass, indicating that early formation alone cannot account for the concentration-dependence in the scatter of the SMHM relation. In contrast, both stellar metallicity and halo concentration exhibit correlations with stellar mass. The connection between halo concentration and stellar metallicity persists even when simultaneously controlling for both halo mass and stellar mass. These results support the scenario in which the deeper gravitational potentials in higher-concentration haloes suppress feedback-driven outflows, thereby enhancing both baryon and metal retention.

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arXiv2026

The evolution of galaxy dust scaling relations in the COLIBRE simulations

We present dust scaling relations across cosmic time ($0 \le z \le 15$) for galaxies in the COLIBRE cosmological simulations. COLIBRE self-consistently tracks dust production, growth, destruction, and grain size evolution within a multiphase interstellar medium. Using volumes up to $(400\, {\rm cMpc})^3$ at three mass resolutions ($10^{5}-10^7$ M$_{\odot}$), we predict the dust mass function, cosmic dust mass density, and key dust scaling relations (dust-to-gas ratio, dust-to-metal ratio, grain species fractions, and grain sizes) as functions of galaxy metallicity, stellar mass, and dust mass. The model broadly reproduces most observed relations across cosmic time, matching closest at the highest resolution. We find that silicates dominate the dust mass ($\gtrsim 70\%$) at all epochs, and while large grains dominate in the early Universe ($z \ge 5$), their mass fraction declines to become comparable to small grains by $z=0$. At $z < 1$, the simulated dust mass functions align well with observations, but the cosmic dust mass density is systematically high by $\lesssim 0.3$ dex, while in agreement with observations at higher redshifts. Additionally, the simulations underpredict the extreme dust masses of bright sub-millimeter galaxies at $z \ge 2$. We demonstrate that scaling relations are sensitive to numerical resolution only in the low-redshift, low-mass regime; while their normalisation is influenced by gas-phase selection. These findings highlight both the predictive power and resolution-dependent limits of cosmological dust models, providing essential insights to refine ISM physics.

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arXiv2026

The evolution of the sizes and angular momentum content of galaxies in the COLIBRE simulations

We analyse the sizes and specific angular momentum content of galaxies in the Colibre cosmological hydrodynamical simulations spanning two orders of magnitude in mass resolution. We compare the predicted size-mass and angular momentum-mass relations to a broad range of observational measurements spanning redshifts $z=0$ to $4$. At $z=0$, Colibre reproduces observed size-mass relations over the sampled mass range $10^8 \lesssim M_\star/{\rm M_\odot}\lesssim 10^{11.5}$, and for multiple size definitions, including two- and three-dimensional stellar half-mass radii, half-light radii across several wavelengths, as well as alternative measures such as baryonic half-mass radii and characteristic radii defined by stellar surface density thresholds. The simulations also recover the observed segregation of galaxies in the size-mass plane by morphological type and star formation rate, and reproduce the distinct, approximately parallel sequences followed by star-forming discs and quenched spheroids in the stellar specific angular momentum-mass plane. The angular momentum content of star-forming Colibre galaxies matches that of observed systems out to $z\approx 1.5$. At higher redshifts, massive galaxies ($ 10^{9.5}\lesssim M_\star/{\rm M_\odot}\lesssim 10^{11}$) in the simulations are somewhat smaller than observed, and the separation between star-forming and passive populations in the size-mass plane is reduced relative to observations, while at lower masses the agreement remains good. This apparent discrepancy may reflect the effects of dust attenuation, which is neglected in our analysis and may preferentially obscure the central regions of observed systems. Overall, our findings highlight the close connection between galaxy size, angular momentum, and morphology over cosmic time.

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arXiv2026

The morphologies of present-day galaxies in the COLIBRE simulations

The diversity of galaxy morphologies and their relations with galaxy and halo properties is fundamental to understanding galaxy formation. Cosmological simulations of representative volumes can help disentangle the origin of observed correlations, but most suffer from two main limitations that affect morphologies: an over-pressurised interstellar medium and spurious interactions between stellar and dark matter particles. We present an overview of galaxy morphologies in the COLIBRE simulations, which address these limitations and reproduce many observed galaxy scaling relations. To quantify galaxy morphology, we use four (strongly-correlated) theory-space metrics, three kinematic and one spatial. We explore how different choices and limitations affect these indicators, including luminosity- versus mass-weighting, aperture size and shot noise. Overall, we find good convergence in present-day morphologies across two orders of magnitude in mass resolution. COLIBRE predicts that kinematic morphology correlates strongly with stellar mass and colour, and that galaxies with stellar masses of $\approx(1-2)\times 10^{10}\,\mathrm{M}_{\odot}$ tend to be the most rotationally-dominated. At fixed stellar mass, the morphology of central galaxies correlates weakly with the properties of their host halo. Morphology correlates more strongly with internal galaxy properties, with more disky galaxies being more gas-rich, having higher star formation rates and exhibiting younger and more extended stellar populations. Other properties, like the mass of the most massive black hole, the fraction of stars that are accreted and stellar metallicity, also correlate with morphology, but with correlation strengths sensitive to the stellar mass of the galaxy and whether it is a central or satellite.

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arXiv2026

The tidal evolution of satellite galaxies in cosmological simulations: insights from COLIBRE

We investigate the co-evolution of the stellar and dark matter mass of satellite galaxies using the COLIBRE cosmological hydrodynamical simulations with subhaloes resolved by the history-based HBT-HERONS subhalo finder. We identify a universal tidal track connecting stellar mass loss to subhalo mass loss characterized by two distinct phases, which can be well described by the two-parameter model. The initial phase consists primarily of dark matter stripping, whereas stellar stripping becomes significant only after the subhalo bound mass fraction drops below a critical value ($\sim 0.057$). We find a bimodal mass loss rate distribution of subhaloes. In satellites with modest mass loss rates, the stellar mass is largely frozen. By contrast, the galaxy quickly becomes unresolved, along with the dark matter component for the extreme-mass-loss population, naturally explaining the lack of ``orphan'' galaxies in previous hydrodynamical simulations. Our model also predicts the formation condition for dark-matter-deficient galaxies (DMDGs), whose abundance peaks at $m_{*}\sim 10^{9.5}\,\rm{M}_{\odot}$. The abundance of DMDGs can be very sensitive to numerical effects, with COLIBRE resolving a much larger DMDG population than previous hydrodynamical simulations. We also estimate the influence of artificial disruption on the satellite stellar mass function, which can amount to 20 (50) per cent at $m_* \sim 10^{9} (10^{8}) \, \rm M_\odot$, given a baryonic mass resolution of $\sim 10^{6}\,\rm{M}_{\odot}$.

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arXiv2026

The COLIBRE-SKIRT pipeline: Calibration-free dust radiative transfer postprocessing for cosmological simulations

Context. Three-dimensional dust radiative transfer provides a powerful framework to connect cosmological galaxy simulations to multiwavelength observations. Until recently, in large-volume simulations, the formation of a cold ISM phase was prevented and dust was not evolved self-consistently. This required calibration of dust-to-metal ratios and extra subgrid dust attenuation in birth clouds, thereby reducing the predictive power. Aims. We present the COLIBRE-SKIRT pipeline, a calibration-free dust radiative transfer framework for the novel COLIBRE suite of large-volume cosmological simulations, which include a live dust model and directly simulate the multiphase ISM. Our primary aim is to establish a reference pipeline for generating multiwavelength mock observables from these simulations. As a first application, we produce far-ultraviolet (FUV) to far-infrared (FIR) spatially integrated spectra and assess them by comparison with the observed low-redshift cosmic spectral energy distribution (CSED). Methods. We apply the SKIRT dust radiative transfer code to the COLIBRE simulations. Dust masses and species fractions are taken directly from the simulation, and no birth cloud model is added in postprocessing. We introduce a "split & scale" approach that maps the simulated two-size, multi-species dust distribution onto continuous grain size distributions without introducing free parameters. Results. We find that, for the first time, a large-volume cosmological simulation directly reproduces the local Universe CSED without calibrating the postprocessing routine a priori. Residual tensions in the mid-infrared (~0.2 dex) point towards insufficient heating of the hottest dust components and uncertainties in the modelling of the PAH-emission carriers. This framework can be readily applied at low and high redshift to create synthetic spectra and images from the FUV to the FIR.

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arXiv2026

Kennicutt-Schmidt relation of galaxies over 13 billion years in the COLIBRE hydrodynamical simulations

We investigate the correlation between star formation rate (SFR) surface density and gas surface density (known as the Kennicutt-Schmidt, KS, relation) at kiloparsec (kpc) scales across cosmic time ($0\le z \le 8$) for galaxies with stellar masses $>10^9\,\rm M_{\odot}$, using the COLIBRE state-of-the-art cosmological hydrodynamical simulations. These simulations feature on-the-fly non-equilibrium chemistry coupled to dust grain evolution and detailed radiative cooling down to $\approx 10$~K, enabling direct predictions for the atomic (HI) and molecular (H$_2$) KS relations. At $z\approx 0$, COLIBRE reproduces the observed (spatially-resolved) KS relations for HI and H$_2$, including the associated scatter, which we predict to be significantly correlated with stellar surface density, local specific SFR (sSFR), and gas metallicity. We show that the HI KS relation steepens for lower-mass galaxies, while the H$_2$ KS relation shifts to higher normalisation in galaxies with higher sSFRs. The H$_2$ depletion time decreases by a factor of $\approx 20$ from $z = 0$ to $z = 8$, primarily due to the decreasing gas-phase metallicity. This results in less H$_2$ and more HI being associated with a given SFR at higher redshift. We also find that galaxies with higher sSFRs have a larger molecular gas content and higher star formation efficiency per unit gas mass on kpc scales. The predicted evolution of the H$_2$ depletion time and its correlation with a galaxy's sSFR agree remarkably well with observations in a wide redshift range, $0\le z\le 5$.

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arXiv2026

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

We investigate the evolution of the galaxy stellar mass function (GSMF) and star formation rates (SFRs) across cosmic time in the COLIBRE simulations of galaxy formation. COLIBRE includes a multiphase interstellar medium, radiative cooling rates coupled to a model for the evolution of dust grains, and employs prescriptions for stellar and AGN feedback calibrated to reproduce the $z=0$ observed GSMF and stellar mass - size relation. We present the evolution of the GSMF from simulations at three resolutions: $m_{\rm gas}\approx m_{\rm dm}\sim 10^7$, $10^6$, and $10^5~\mathrm{M_\odot}$, in cosmological volumes of up to $400^3$, $200^3$, and $100^3$ cMpc$^3$, respectively. We demonstrate that COLIBRE is consistent with the observed GSMF over the full redshift range for which there are observations to compare with ($0<z<12$), with maximum systematic deviations of $\approx 0.3$ dex reached at $2<z<4$. We also examine the evolution of the star-forming main sequence, cosmic SFR density, stellar mass density, and galaxy quenched fraction, making predictions for both the fiducial COLIBRE model with thermally-driven AGN feedback and its variant with hybrid (thermal + kinetic jet) AGN feedback, and finding good agreement with observations. Notably, we show that COLIBRE matches the number density of massive quiescent galaxies at high redshifts reported by JWST, while predicting a stellar-to-halo mass relation that evolves little with redshift. We conclude that neither a redshift-dependent star formation efficiency, nor a variable stellar initial mass function, nor a deviation from $Λ\mathrm{CDM}$ is necessary to reproduce the high-redshift JWST stellar masses and SFRs.

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arXiv2026

A subgrid model for chemical enrichment in cosmological simulations

We present the modules for stellar nucleosynthesis, stellar mass loss, and turbulent diffusion of the new COLIBRE subgrid model for cosmological hydrodynamical simulations of galaxy formation. COLIBRE models the thermal evolution of the multi-phase interstellar medium, dust grains, star formation, and stellar and AGN feedback. This work focuses on the model for chemical enrichment. We track the evolution of 12 chemical elements produced by a broad range of nucleosynthetic channels, including core-collapse supernovae and stellar winds, Type Ia supernovae, and asymptotic giant branch (AGB) stars. Enrichment from $s$- and $r$-process elements is modelled via contributions from AGB stars, neutron star mergers, common envelope supernovae, and collapsars. We present an updated compilation of stellar yields taken from the literature, which we release alongside this work. Small-scale element mixing is implemented through a turbulent diffusion process. While diffusion has only a minimal impact on basic integrated galaxy properties, it does reduce the slope of the gas-phase metallicity-mass relation compared with simulations that do not include it. The distribution of element ratios of individual stellar particles is sensitive to diffusion, but only at low metallicities ($Z \lesssim 10^{-1}\,\rm{Z}_\odot$). The model is tested using redshift $z=0$ results from a set of cosmological simulations, mostly of (25 Mpc)$^3$ volumes, demonstrating generally good agreement with Milky Way stellar abundance trends from the APOGEE survey. The model also reproduces the alpha-element enhancement relations observed in galaxies from SDSS, ATLAS-3D, and the Local Group.

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arXiv2026

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

We present the calibration of stellar and active galactic nucleus (AGN) feedback in the subgrid model for the new COLIBRE hydrodynamical simulations of galaxy formation. COLIBRE directly simulates the multi-phase interstellar medium and the evolution of dust grains, which is coupled to the chemistry. COLIBRE is calibrated at three resolutions: particle masses of $m_{\rm gas} \approx m_{\rm dm} \sim 10^7$ (m7), $10^6$ (m6), and $10^5~\mathrm{M_\odot}$ (m5). To calibrate the COLIBRE feedback at m7 resolution, we run Latin hypercubes of $\approx 200$ simulations that vary up to four subgrid parameters in cosmological volumes of ($50~\mathrm{cMpc}$)$^{3}$. We train Gaussian process emulators on these simulations to predict the $z=0$ galaxy stellar mass function (GSMF) and size - stellar mass relation (SSMR) as functions of the model parameters, which we then fit to observations. The trained emulators not only provide the best-fitting parameter values but also enable us to investigate how different aspects of the prescriptions for supernova and AGN feedback affect the predictions. In particular, we demonstrate that while the observed $z=0$ GSMF and SSMR can be matched individually with a relatively simple supernova feedback model, simultaneously reproducing both necessitates a more sophisticated prescription. We show that the calibrated m7 COLIBRE model not only reproduces the calibration target observables, but also matches various other galaxy properties to which the model was not calibrated. Finally, we apply the calibrated m7 model to the m6 and m5 resolutions and, after slight manual adjustments of the subgrid parameters, achieve a similar level of agreement with the observed $z=0$ GSMF and SSMR.

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arXiv2026

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

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.

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arXiv2026

A hybrid active galactic nucleus feedback model with spinning black holes, winds and jets

We present a hybrid active galactic nucleus (AGN) feedback model that features three accretion disc states (the thick, thin, and slim discs at low, moderate, and super-Eddington accretion rates, respectively), and two feedback modes: thermal isotropic and kinetic jets. The model includes black hole (BH) spin evolution due to gas accretion, BH mergers, jet spindown, and Lense-Thirring torques. The BH spin determines the jet directions and affects the feedback efficiencies. The model is implemented in the SWIFT code and coupled with the COLIBRE galaxy formation model. We present the first results from hybrid AGN feedback simulations run as part of the COLIBRE suite, focusing on the impact of new parameters and calibration efforts. Using the new hybrid AGN feedback model, we find that AGN feedback affects not just massive galaxies, but all galaxies down to $M_*\approx10^8$ $\mathrm{M}_\odot$. BH spins are predicted to be near-maximal for intermediate-mass BHs ($M_\mathrm{BH}\in[10^6,10^8]$ $\mathrm{M}_\odot$), and lower for other BH masses. These trends are in good agreement with observations. The intergalactic medium is hotter and impacted on larger scales in the hybrid AGN feedback simulations compared to those using purely thermal feedback. In the hybrid AGN simulations, we predict that half of the cumulative injected AGN energy is in thermal and the other half in jet form, broadly independent of BH mass and redshift. Jet feedback is important at all redshifts and dominates over thermal feedback at $z<0.5$ and $z>1.5$, but only mildly.

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arXiv2026

Non-explosive pre-supernova feedback in the COLIBRE model of galaxy formation

We present the implementation and testing of a subgrid non-explosive pre-supernova (NEPS) feedback module for the COLIBRE model of galaxy formation. The NEPS module incorporates three key physical processes sourced by young, massive stars that act immediately following star formation: momentum injection from stellar winds and radiation pressure, and thermal energy from photoheating in HII regions. The age- and metallicity-dependent energy and momentum budgets are derived from BPASS stellar population models and are coupled self-consistently to the local gas properties. We test the model using a suite of smoothed particle hydrodynamics simulations of isolated, unstable gaseous disks at various numerical resolutions (gas particle masses in the range $10^4-10^6$ $\rm M_{\odot}$). We find that the NEPS module successfully regulates star formation by providing pressure support that prevents catastrophic gas collapse. This regulation improves the numerical convergence of star formation rates and disk structure. In our model, feedback from HII regions is the dominant regulatory mechanism. Furthermore, we demonstrate a crucial synergy with subsequent supernova feedback; NEPS feedback pre-processes the interstellar medium, creating a more homogeneous environment that moderates the effect of explosive feedback from supernova events. Our NEPS module thus provides a physically motivated and numerically robust framework that mitigates resolution-dependent artefacts and promotes self-regulated galaxy growth.

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