Recent James Webb Space Telescope observations hint at unexpectedly intense cosmic star formation in the early Universe, often attributed to enhanced star formation efficiencies (SFEs). Here, we analyse the SFE in THESAN-ZOOM, a novel zoom-in radiation-hydrodynamic simulation campaign of high-redshift (z greater than or similar to 3) galaxies employing a state-of-the-art galaxy formation model resolving the multiphase interstellar medium (ISM). The halo-scale SFE (is an element of(halo)*) the fraction of baryons accreted by a halo that are converted to stars follows a double power-law dependence on halo mass, with a mild redshift evolution above M-halo greater than or similar to 10(95) M-circle star. The power-law slope transitions from similar to 2/3 to similar to 1/3 as halo mass increases, which hints at a transition from energy-driven to momentum-driven outflow. is an element of(halo)* is a factor of 2-3 larger than commonly assumed in empirical galaxy formation models at M-halo less than or similar to 10(95) M-circle star. On galactic (pkpc) scales, the Kennicutt-Schmidt relation of neutral gas is universal in THESAN-ZOOM, following Sigma(SFR) alpha Sigma(2)(gas), indicative of a turbulent energy balance in the ISM maintained by stellar feedback. The rise of is an element of(halo)* with halo mass can be traced primarily to increasing gas surface densities in massive galaxies. These results are is an element of(halo)* primarily increasing gas galaxies. robust against variations in numerical resolution and star formation and feedback models, depending mainly on the total feedback momentum budget. Although the increase in is an element of(halo)* with redshift is modest, it is sufficient to explain the large observed number density of UV-bright galaxies at z >= 12. However, reproducing the brightest sources at M-UV less than or similar to-21 may require extrapolating the SFE beyond the halo mass range covered by THESAN-ZOOM.

Metal absorbers represent a powerful probe of galaxy feedback and reionization, as highlighted by both observational and theoretical results showing an increased abundance of low-ionized metal species at higher redshifts. The origin of such absorbers is currently largely unknown because of the low number of galaxy counterparts detected, suggesting that they might be surrounded by low-mass faint sources below the current detection threshold. We use the THESAN-ZOOM radiation hydrodynamic simulations to investigate the connection between properties of neutral oxygen (O-1) absorbers and galaxies across redshift z approximate to 5-8 . We find that the virialized gas in haloes becomes progressively ionized with cosmic time, leading to a decrease of ti 0.2 in the covering fraction of neutral oxygen, while the total oxygen covering fraction remains constant. Comparing the O-1 line density obtained from our covering fractions with the trend suggested by blind quasar observations, we determine that the observable absorbers (N-OI greater than or similar to 10(13) cm(-2)) are not confined to haloes: atz >= 5 the majority (greater than or similar to 60 per cent ) arise beyond Rvir, consistent with recent James Webb Space Telescope (JWST) results. Close to O-1 absorbers, low-mass galaxies (M-star <= 10(8) M-circle dot) are more commonly found, while, depending on the simulated environment, we do not exclude the possibility of nearby more massive star-forming sources (>= 5 M-circle dot yr(-1)) similar to those suggested by the latest ALMA observations. These results establish O-1 absorbers as sensitive tracers of the evolving ionisation structure around faint galaxies to be probed by forthcoming deep spectroscopic surveys.

Understanding the sources and evolution of cosmic reionization remains a central challenge in astrophysics, with the escape of ionizing Lyman-continuum (LyC) photons from early galaxies representing a major uncertainty. In this work, we use more than 35,000 galaxy realisations from the THESAN-ZOOM cosmological radiation-hydrodynamic simulations to identify indirect diagnostics of the LyC photon escape fraction (f_esc) and the LyC photon escape rate (Ṅ_ion,esc) across the redshift range z=3-16. We train random forest regression models using these diagnostics to predict both quantities. We present four models: two trained with the full set of simulation-derived indicators to predict f_esc and Ṅ_ion,esc, and two restricted to observables accessible to JWST photometric surveys. We find the 10-to-100Myr star-formation rate ratio (SFR_10 / SFR_100) and the gas-to-stellar mass ratio (M_gas / M_*) to be the strongest diagnostics of f_esc, suggesting a strong relationship between ionizing photon escape and gas clearing through bursty star formation. In contrast, rest-frame UV (1500 Å) absolute magnitude (M_UV) dominates Ṅ_ion,esc prediction. Motivated by the strong predictive power of M_UV, we combine observed UV luminosity functions with derived Ṅ_ion,esc - M_UV relations to construct histories of reionization. These are consistent with observational constraints, avoiding the recently reported crisis in the ionizing photon budget. Our analysis suggests that the bulk of reionization occurred rapidly after z ≈ 8, driven by UV-bright galaxies, with the M_UV < -17 populations providing the dominant contribution.

The dispersion of fast radio bursts (FRBs) measures the column density of free electrons, tracing the diffuse ionized gas that contains more than 90% of all baryons. On linear scales the FRB dispersion field is an approximately unbiased tracer of the matter distribution, an idea long assumed in the FRB large-scale structure literature and recently formalized by Zhou and Zhang [arXiv:2510.11022]. This follows from baryon-mass conservation, which forces the total baryon field to have unit linear bias, with dispersion inheriting this bias up to small corrections from the stellar and neutral-gas components. We show these corrections can be bounded at the percent level using existing galaxy and 21 cm surveys, and confirm with the FLAMINGO hydrodynamical simulations that the electron bias varies at the percent level across a wide range of feedback prescriptions. The dispersion-galaxy cross-power spectrum at linear scales directly constrains B_8 ≡ σ_8(Ω_b/0.05)^1/2, a baryonic analog of S_8, independently of feedback physics. Because most of the per-object variance in dispersion is cosmological signal rather than noise, ∼10^5 localized FRBs can match the statistical power of ∼10^8 weak-lensing galaxy shape measurements. FRB dispersion thus joins weak lensing and redshift-space distortions as a new unbiased tracer of matter on large scales.

The complex processes of baryonic feedback associated with galaxy evolution are still poorly understood, and their impact on the clustering of matter on small scales remains difficult to quantify. While many fitting functions and emulators exist to model the matter power spectrum, their input parameters are not directly observable. However, recent studies using hydrodynamical simulations have identified a promising correlation between the gas content of halos and changes to the matter power spectrum from feedback. Building on these findings, we create the first fully data-driven power spectrum emulator. We utilize the kinematic Sunyaev-Zel'dovich (kSZ) effect, a secondary anisotropy in the cosmic microwave background, as a tracer of free electrons in and around halos. We train a neural network to learn the mapping between the suppression of the matter power spectrum and the shape of the kSZ power spectrum extracted with a radial velocity template. We train and validate our algorithm using the FLAMINGO suite of hydrodynamical simulations, which encompasses a wide range of feedback models. Our emulator can reconstruct the matter power spectrum at the subpercent level for scales k <= 5 h/Mpc and 0.2 <= z <= 1.25 directly from the data. Our model is robust and retains percent-level accuracy even for feedback models and cosmological parameter values not seen during training (except in a few extreme cases drastically different from the fiducial model). Due to its robustness, our algorithm offers a new way to identify the sources of suppression in the matter power spectrum, breaking the degeneracies between baryonic feedback and new physics. Finally, we present a forecast for reconstruction of the matter power spectrum combining maps of the microwave background anisotropies from a Simons Observatory-like experiment and galaxy catalogs from the Dark Energy Spectroscopic Instrument.

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 multiphase interstellar medium and the evolution of dust grains, which is coupled to the chemistry. COLIBRE is calibrated at three resolutions: particle masses of m(gas )approximate to m(dm) similar to 10(7 )(m7), 10(6) (m6), and 10(5) M-circle dot (m5). To calibrate the COLIBRE feedback at m7 resolution, we run Latin hypercubes of approximate to 200 simulations that vary up to four subgrid parameters in cosmological volumes of ( 50 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.

We present an analysis of metallicities and chemical abundances at 3 < z < 12 in the THESAN-ZOOM simulations. We find that smoothly curved gas-phase and stellar mass-metallicity relations are already in place at z approximate to 12 and evolve slowly (similar to 0.2 dex increase for gas, similar to 0.4 dex increase for stars at a fixed stellar mass) down to z = 3 , governed largely by the efficiency with which galaxies retain their metals, rather than gas fraction. The canonical fundamental metallicity relation survives in stars but breaks down and inverts for gas in low-mass galaxies ( M (*)less than or similar to 10(9)M(circle dot)) due to regular dilution by low-metallicity gas inflow. We find broad agreement of gas-phase N/O, Fe/O, and C/O with high-redshift observations, including the presence of nitrogen-rich galaxies (NRGs; log(N / O ) > -0.6) without the need for exotic yields in our chemical network. Instead, bursty star formation naturally generates order-of-magnitude excursions in N/O on less than or similar to 100 Myr time-scales due to temporally differential galactic winds; after a starburst, stellar feedback expels gas, leaving a large population of asymptotic-giant-branch stars to dominate the enrichment of the relatively low-mass interstellar medium. NRGs lie below the main sequence and typically exhibit EW[H beta] less than or similar to 40 angstrom, in apparent tension with observed high-EW NRGs. This tension is reconciled if observed NRGs are in the initial stages of a subsequent starburst, illuminating previously enriched gas, which is supported by the finding of high SFR surface density nitrogen-rich giant molecular clouds.

Globular clusters exhibit large star-to-star variations and anticorrelations in their light element abundances that are commonly interpreted in terms of in-cluster self-enrichment, in which ejecta from early-forming cluster stars pollute the gas from which later stars form over millions of years. Yet proposed self-enrichment scenarios suffer from a severe mass-budget problem or invoke exotic stellar populations. Using cosmological radiation-hydrodynamic simulations with a standard chemical enrichment model, we identify a population of giant molecular clouds whose internal abundance patterns reproduce several key globular cluster signatures: large light-element abundance spreads and nitrogen-oxygen anticorrelations at nearly constant iron abundance. These clouds form at the restart of star-formation activity after an earlier starburst, where previously ejected oxygen-rich gas collides with nitrogen-rich galactic gas, and are sites of dense star-cluster formation. In this picture, the chemical abundance patterns of globular clusters need not require extended in-cluster star formation, but can be inherited at birth from chemically structured interstellar gas shaped by the baryon cycle. Globular clusters therefore provide a fossil record of chemical enrichment and gas flows in high-redshift galaxies.

Recent JWST observations have revealed diverse high-redshift galaxy morphologies, including a population with irregular and clumpy structures. The physical origin of these structures, and the extent to which observational biases shape their appearance, remain uncertain. We present a power-spectrum-based method for quantifying galaxy clumpiness across spatial scales, using the radiation-hydrodynamic simulation suite THESAN-ZOOM, which employs a state-of-the-art galaxy formation model that resolves the multiphase interstellar medium (ISM). Although the total stellar mass distributions in THESAN-ZOOM galaxies are usually smooth, clumpy structures appear in the Hα, far-ultraviolet (FUV), and optical light distributions. Tracers sensitive to shorter-timescale star formation exhibit more pronounced small-scale structure (∼10^2–10^3 pc). The corresponding projected light spectra follow P(k)∝ k^-1 to k^-2, with progressively shallower slopes for tracers sensitive to more recent star formation, reflecting enhanced small-scale power and greater spatial intermittency in young stellar populations. This behaviour is consistent with a highly compressible, shock-dominated ISM in which stellar feedback and outflows reorganise dense gas into filamentary and clumpy structures. We also find that galaxy clumpiness depends on the treatment of stellar feedback. Weaker early stellar feedback enhances small-scale power in both the mass and light distributions. Clumpiness also varies strongly over the bursty star formation cycle, implying that observed samples may be biased towards galaxies caught in phases of elevated star formation. Galaxy clumpiness, therefore, could provide a complementary probe of the bursty star formation in the early Universe.

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 approximate to 0 galaxy stellar mass function, galaxy sizes, and black hole masses in massive galaxies. The COLIBRE suite includes three resolutions, with particle masses of similar to 10(5), 10(6) , and 10(7)M(circle star) 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.

We present an analysis of metallicities and chemical abundances at 3-0.6) without the need for exotic yields in our chemical network. Instead, bursty star formation naturally generates order-of-magnitude excursions in N/O on ≲100 Myr timescales due to temporally differential galactic winds; after a starburst, stellar feedback expels gas, leaving a large population of asymptotic-giant-branch stars to dominate the enrichment of the relatively low-mass interstellar medium. NRGs lie below the main sequence and typically exhibit EW[Hβ]≲40 Å, in apparent tension with observed high-EW NRGs. This tension is reconciled if observed NRGs are in the initial stages of a subsequent starburst, illuminating previously enriched gas, which is supported by the finding of high SFR surface density nitrogen-rich giant molecular clouds.

The splashback radius is one popular method of constraining the size of galaxy clusters, often measured through the logarithmic derivative of the galaxy number density profile. However, measuring the splashback radius through the galaxy number density has consistently produced smaller values of the splashback radius than those inferred from the underlying gravitational potential in simulations. Dynamical friction has been posited as one possible reason that splashback radii measured through galaxy number densities are reduced, since it decays the orbits of subhaloes within the halo. Dynamical friction is an emergent process, and as such, cannot be isolated or removed within N-body simulations. Here, we present simulations starting with isolated galaxy clusters drawn from the IllustrisTNG cosmological simulation, where we explicitly control dynamical friction through an idealized model. We show that although dynamical friction can reduce measurements of the splashback radius, it does not have a significant effect on clusters with M_200,mean > 10^14M_⊙, and thus cannot account for previously measured discrepancies.

High-redshift active galactic nuclei (AGN) have long been recognized as key probes of early black hole growth and galaxy evolution. However, modeling this population remains difficult due to the wide range of luminosities and black hole masses involved, and the high computational costs of capturing the hydrodynamic response of gas and evolving radiation fields on-the-fly. In this study, we present a new suite of simulations based on the IllustrisTNG galaxy formation framework, enhanced with on-the-fly radiative transfer, to examine AGN at high redshift (z > 5) in a protocluster environment extracted from the MillenniumTNG simulation. We focus on the co-evolution of black holes and their host galaxies, as well as the radiative impact on surrounding intergalactic gas. The model predicts that black holes form in overdense regions and lie below the local black hole-stellar mass relation, with stellar mass assembly preceding significant black hole accretion. Ionizing photons are primarily produced by stars, which shape the morphology of ionized regions and drive reionization. Given the restrictive black hole growth in the original IllustrisTNG model, we reduce the radiative efficiency from 0.2 to 0.1, resulting in higher accretion rates for massive black holes, more bursty growth, and earlier AGN-driven quenching. However, the resulting AGN remain significantly fainter than observed high-redshift quasars. As such, to incorporate this missing population, we introduce a quasar boosted model, in which we artificially boost the AGN luminosity. This results in strong effects on the surrounding gas, most notably a proximity effect, and large contributions to He ionization.

Star formation in galaxies is inherently complex, involving the interplay of physical processes over a hierarchy of spatial scales. In this work, we investigate the connection between global (galaxy-scale) and local (cloud-scale) star formation efficiencies (SFEs) at high redshifts (z greater than or similar to 3), using the state-of-the-art cosmological zoom-in simulation suite THESAN-ZOOM. We find that the galaxy-scale average SFE, ((gal)(ff) ) , scales with M-halo(1/3) (1 + z)(1 / 2) similar to V-vir, consistent with expectations from feedback-regulated models. On cloud scales, we identify giant molecular clouds (GMCs) in a broad sample of high-redshift starbursts spanning a wide range of halo masses and redshifts. Star formation in these systems is predominantly hosted by filamentary GMCs embedded in a dense and highly turbulent interstellar medium (ISM). GMCs exhibit remarkably universal properties, including mass function, size, turbulence, and surface density, regardless of the environment in which they are identified. The global gas depletion time (and the Kennicutt-Schmidt relation) is determined by the GMC mass fraction in the ISM, while the cloud-scale SFE shows little variation. In particular, we find a nearly constant gas surface density of E-GMC approximate to 70 M-circle dot pc(-2) across different host galaxies. Nevertheless, we identify two regimes where phases with high SFE can arise. First, stars may form efficiently in the shock fronts generated by feedback from a preceding starburst. Secondly, the increasing background dark matter surface density with redshift may contribute to the gravitational potential of clouds at z greater than or similar to 8 and confine them in high-SFE phases over extended periods.

Characterizing the evolution of the star-forming main sequence (SFMS) at high redshift is crucial to contextualize the observed extreme properties of galaxies in the early Universe. We present an analysis of the SFMS and its scatter in the THESAN-ZOOM simulations, where we find a redshift evolution of the SFMS normalization scaling as $\propto (1+z)^{2.64\pm0.03}$, significantly stronger than is typically inferred from observations. We can reproduce the flatter observed evolution by filtering out weakly star-forming galaxies, implying that current observational fits are biased due to a missing population of lulling galaxies or overestimated star-formation rates. We also explore star-formation variability using the scatter of galaxies around the SFMS ($\sigma_{\mathrm{MS}}$). At the population level, the scatter around the SFMS increases with cosmic time, driven by the increased importance of long-term environmental effects in regulating star formation at later times. To study short-term star-formation variability, or ''burstiness'', we isolate the scatter on timescales shorter than 50 Myr. The short-term scatter is larger at higher redshift, indicating that star formation is indeed more bursty in the early Universe. We identify two starburst modes: (i) externally driven, where rapid large-scale inflows trigger and fuel prolonged, extreme star formation episodes, and (ii) internally driven, where cyclical ejection and re-accretion of the interstellar medium in low-mass galaxies drive bursts, even under relatively steady large-scale inflow. Both modes occur at all redshifts, but the increased burstiness of galaxies at higher redshift is due to the increasing prevalence of the more extreme external mode of star formation.

Self-interacting dark matter (SIDM) has the potential to significantly influence galaxy formation in comparison to the cold, collisionless dark matter paradigm (CDM), resulting in observable effects. This study aims to elucidate this influence and to demonstrate that the stellar mass Tully-Fisher relation imposes robust constraints on the parameter space of velocity-dependent SIDM models. We present a new set of cosmological hydrodynamical simulations that include the SIDM scheme from the TangoSIDM project and the SWIFT-EAGLE galaxy formation model. Two cosmological simulations suites were generated: one (Reference model) which yields good agreement with the observed $z=0$ galaxy stellar mass function, galaxy mass-size relation, and stellar-to-halo mass relation; and another (WeakStellarFB model) in which the stellar feedback is less efficient, particularly for Milky Way-like systems. Both galaxy formation models were simulated under four dark matter cosmologies: CDM, SIDM with two different velocity-dependent cross sections, and SIDM with a constant cross section. While SIDM does not modify global galaxy properties such as stellar masses and star formation rates, it does make the galaxies more extended. In Milky Way-like galaxies, where baryons dominate the central gravitational potential, SIDM thermalises, causing dark matter to accumulate in the central regions. This accumulation results in density profiles that are steeper than those produced in CDM from adiabatic contraction. The enhanced dark matter density in the central regions of galaxies causes a deviation in the slope of the Tully-Fisher relation, which significantly diverges from the observational data. In contrast, the Tully-Fisher relation derived from CDM models aligns well with observations.

We explore the evolution of galaxy sizes at high redshift (3 < z < 13) using the high-resolution THESAN-ZOOM radiation-hydrodynamics simulations, focusing on the mass range of 10(6) M-circle dot < M-* < 10(10 )M(circle dot). Our analysis reveals that galaxy size growth is tightly coupled to bursty star formation. Galaxies above the star-forming main sequence tend to form stars in a central starburst, which decreases their radial size. These galaxies quench inside-out, causing spatially extended star formation and increasing their radial size, leading to oscillatory behaviour around the size-mass relation. Notably, we find a positive intrinsic size-mass relation at high redshift, consistent with observations but in tension with large-volume simulations. We attribute this discrepancy to the bursty star formation captured by our multiphase interstellar medium framework, but missing from simulations using the effective equation-of-state approach with hydrodynamically decoupled feedback. We also find that the normalization of the size-mass relation follows a double power law as a function of redshift, with a break at z approximate to 6, because the majority of galaxies at z > 6 show rising star-formation histories, and therefore are in a compaction phase. We demonstrate that H alpha emission is systematically extended relative to the UV continuum by a median factor of 1.7, consistent with recent James Webb Space Telescope studies. However, in contrast to previous interpretations that link extended H alpha sizes to inside-out growth, we find that Lyman-continuum (LyC) emission is spatially disconnected from H alpha. Instead, a simple Stromgren sphere argument reproduces observed trends, suggesting that extreme LyC production during central starbursts is the primary driver of extended nebular emission.

We introduce the THESAN-ZOOM project, a comprehensive suite of high-resolution zoom-in simulations of $14$ high-redshift ($z>3$) galaxies selected from the THESAN simulation volume. This sample encompasses a diverse range of halo masses, with $M_\mathrm{halo} \approx 10^8 - 10^{13}~\mathrm{M}_\odot$ at $z=3$. At the highest-resolution, the simulations achieve a baryonic mass of $142~\mathrm{M}_\odot$ and a gravitational softening length of $17~\mathrm{cpc}$. We employ a state-of-the-art multi-phase interstellar medium (ISM) model that self-consistently includes stellar feedback, radiation fields, dust physics, and low-temperature cooling through a non-equilibrium thermochemical network. Our unique framework incorporates the impact of patchy reionization by adopting the large-scale radiation field topology from the parent THESAN simulation box rather than assuming a spatially uniform UV background. In total, THESAN-ZOOM comprises $60$ simulations, including both fiducial runs and complementary variations designed to investigate the impact of numerical and physical parameters on galaxy properties. The fiducial simulation set reproduces a wealth of high-redshift observational data such as the stellar-to-halo-mass relation, the star-forming main sequence, the Kennicutt-Schmidt relation, and the mass-metallicity relation. While our simulations slightly overestimate the abundance of low-mass and low-luminosity galaxies they agree well with observed stellar and UV luminosity functions at the higher mass end. Moreover, the star-formation rate density closely matches the observational estimates from $z=3-14$. These results indicate that the simulations effectively reproduce many of the essential characteristics of high-redshift galaxies, providing a realistic framework to interpret the exciting new observations from JWST.

We investigate the impact of ionizing external ultraviolet (UV) radiation on low-mass haloes (M-halo less than or similar to 10(10) M-circle dot) at high redshift ( z >= 3) using 1140 M-circle dot baryonic resolution zoom-in simulations of seven THESAN-ZOOM regions. We compare three simulation sets that differ in the treatment of external UV radiation: one employing a uniform UV background initiated at z = 10 . 6 in addition to radiation transport for local sources, another with the background starting at z = 5 . 5, and the default configuration using the large-scale radiation from the parent THESAN-1 simulation as a boundary condition. The multiphase interstellar medium (ISM) model, combined with its high mass resolution, allows us to resolve all star-forming haloes and capture the back-reaction of ionizing radiation on galaxy properties during the epoch of reionization. When present, external UV radiation efficiently unbinds gas in haloes with masses below 10(9) M-circle dot and suppresses subsequent star formation. As a result, in simulations with early reionization, minihaloes fail to form stars from pristine gas, leading to reduced metal enrichment of gas later accreted by more massive haloes. Consequently, haloes with masses below 10(10) M-circle dot at all simulated epochs ( z > 3) exhibit lower metallicities and altered metallicity distributions. The more accurate and realistic shielding from external UV radiation, achieved through self-consistent radiative transfer, permits the existence of a cold but low-density gas phase down to z = 3. These findings highlight the importance of capturing a patchy reionization in high-resolution simulations targeting high-redshift galaxy formation. We conclude that at minimum, semi-numerical models that incorporate spatially inhomogeneous reionization and a non-uniform metallicity floor are necessary to accurately emulate metal enrichment in minihaloes.

Baryonic feedback is a leading contaminant in studying dark matter and cosmology using cosmic shear. This has meant omitting much of the data during cosmological inference, or forward-modeling the spatial distribution of gas around dark matter halos using analytical or hydrodynamical models for baryonic feedback, which introduces nuisance parameters and model dependence. We propose a novel method of “baryon nulling” using cross-correlations between shear maps and fast radio burst (FRB) dispersion measures. By directly subtracting the dark matter–dispersion measure cross-correlation, the sensitivity of our nulled power spectra to feedback effects can be significantly reduced without any explicit feedback modeling. Using the FLAMINGO suite of hydrodynamic simulations, whose power spectra span a wide yet realistic range of feedback variations, we demonstrate that our method reduces sensitivity to feedback modeling at k ≈ 1 Mpc^-1 by about an order of magnitude. This points toward a strong synergy between the next generation of sensitive FRB surveys such as CHORD and the DSA-2000, and cosmic shear surveys such as Rubin, Euclid, and Roman.