We present results of Population III (Pop III) formation in the MEGATRON suite of simulations, which self-consistently follows radiation and non-equilibrium chemistry, and resolves gas at near-pc resolution in a Milky Way-mass progenitor at Cosmic Dawn. While the very first Pop III stars form in haloes with masses well below the atomic cooling limit, the majority of Pop III stars form in more massive systems above the 10 (4) K atomic cooling threshold as a Lyman-Werner (LW) background of 10(-21) erg s(-1) cm(-2) Hz(-1) sr(-1) is rapidly established. We find that the global Pop III star formation rate stabilizes to a value of 10(-3) M circle dot yr(-1) at z = 20 . Among the three processes that quench Pop III star formation in minihaloes, the LW background, gas starvation, and external chemical enrichment, the LW background is most important. A small fraction of haloes undergo multiple episodes of Pop III star formation when the earlier forming stars all directly collapse to black holes. If the haloes become massive enough, they can form up to similar to 100 Pop III stars in a single burst, which may be observable by James Webb Space Telescope with moderate gravitational lensing. Pop III stars form at a wide range of distances from UV-bright galaxies, with only 0 . 06 per cent of Pop III stars forming within the virial radius of galaxies with M-UV< -17. Finally, by tracking Pop III star remnants down to z = 0 , we find that 75-80 per cent reside in the stellar halo of our simulated Milky Way analogue, while the remainder are gravitationally bound to lower mass systems, including satellite haloes.

Jellyfish galaxies provide direct evidence of ram pressure stripping in cluster environments. We investigate the role of magnetic fields in the formation of jellyfish galaxies with a multiphase interstellar medium (ISM) using radiation magnetohydrodynamic simulations. We impose magnetized (magnetohydrodynamic; MHD) and nonmagnetized (hydrodynamic; HD) winds on the gas-rich dwarf galaxies containing the magnetized or nonmagnetized ISM. The MHD winds strip the disk gas more effectively than the HD winds because of the magnetic force acting against the local density gradient, which results in remarkably different ram pressure stripped features. The magnetic fields induced by the MHD winds generate a strong magnetic pressure, which forms smoothed disks and tail gas features. Since the stripped ISM in MHD wind cases travels while being nearly isolated from the intracluster medium (ICM), the stripped ISM mostly forms stars within 20 kpc of the galactic disks. In contrast, nonmagnetized winds facilitate the efficient mixing of the stripped ISM with the ICM, resulting in the formation of abundant warm clouds that cool and collapse in the distant (∼50–100 kpc) tails at times of a few hundred Myr. Consequently, distant tail star formation occurs only in the HD wind runs. Finally, despite the different tail features, the star formation rates in the disk remain similar owing to the interplay between the increased gas stripping and the gas density increase in the disks of the MHD wind runs. These results suggest that the magnetized ICM may have a significant influence on jellyfish galaxies, whereas the magnetized ISM play a minor role.

Dust grains and polycyclic aromatic hydrocarbons (PAHs) actively contribute to the thermodynamics, chemistry, and radiative state of the interstellar medium (ISM), yet most ISM models and galaxy simulations either exclude them altogether or adopt simplified treatments. We present CALIMA, a new module for dust and PAH formation and evolution in radiation-hydrodynamics simulations for RAMSES, designed to self-consistently couple dust physics to radiative transfer and non-equilibrium thermochemistry in a multiphase ISM. The model employs a two-size, two-composition dust framework with log-normal grain populations, explicitly evolving stellar dust injection, turbulence-informed gas-phase accretion, shattering, coagulation, thermal and non-thermal sputtering, and shock destruction, while PAHs are separate components with their own evolution. The evolving dust populations and radiation field determine local, wavelength-dependent opacities, photoelectric heating efficiencies, grain-assisted recombination, dust-gas collisional heating/cooling, and H_2 formation on both grains and PAHs. Updated treatments of thermal sputtering and collisional cooling that include finite grain sizes and modern ion-solid physics reduce sputtering rates at high temperatures and extend the regime where dust significantly cools hot gas. One-zone ISM tests show that dust and PAH evolution modifies classical thermal phase diagrams and C-bearing chemistry, while isolated disc galaxy simulations reveal environment-dependent variations in dust-to-metal ratio, small-to-large grain ratio, PAH fraction, and interstellar radiation field intensity that drive non-trivial structure in infrared emission, UV transparency, and H_2 formation. CALIMA provides a physically motivated framework to interpret dust- and PAH-based observables and to assess dust-mediated feedback in galaxy formation across cosmic time.

Now detected out to redshifts of $z\sim 14.5$, the rest-frame ultraviolet and optical spectra of galaxies encode numerous physical properties of the interstellar medium (ISM). Accurately extracting these properties from spectra remains a key challenge that numerical simulations are uniquely suited to address. We present a study of the observed ISM of galaxies in MEGATRON: a suite of cosmological radiation hydrodynamics simulations coupled to on-the-fly non-equilibrium thermochemistry, with multiple prescriptions for star formation/feedback and parsec-scale resolution; capable of directly predicting spectroscopic properties of early galaxies. We find that irrespective of feedback physics used, the ISM of high-redshift galaxies is denser, less metal enriched, and subject to higher ionization parameters and radiation fields compared to similar mass galaxies in the local Universe -- in agreement with interpretations of JWST observations. Using common observational techniques to infer bulk galaxy properties, we find that ISM gas density controls the slope of the mass-metallicity relation. Similarly, at the densities reached in some high-redshift galaxies, O32 becomes a density tracer rather than one of ionization parameter. This motivates the use of other line ratios like C43 and N43 to infer the ionization state of the gas. Finally, various feedback models populate different regions of strong-line diagnostic diagrams as the line ratios are sensitive to the feedback-modulated density-temperature structure of the ISM. Therefore, observed strong-line diagnostics can provide a strong constraint on the underlying physics of star formation and feedback in the high-redshift Universe.

The peculiar velocity field of the local Universe provides direct insights into its matter distribution and the underlying theory of gravity, and is essential in cosmological analyses for modelling deviations from the Hubble flow. Numerous methods have been developed to reconstruct the density and velocity fields at z less than or similar to 0.05, typically constrained by redshift-space galaxy positions or by direct distance tracers such as the Tully-Fisher relation, the Fundamental Plane, or Type Ia supernovae. We introduce a validation framework to evaluate the accuracy of these reconstructions against catalogues of direct distance tracers. Our framework assesses the goodness-of-fit of each reconstruction using Bayesian evidence, residual redshift discrepancies, velocity scaling, and the need for external bulk flows. Applying this framework to a suite of reconstructions - including those derived from the Bayesian Origin Reconstruction from Galaxies (BORG) algorithm and from linear theory - we find that the non-linear BORG reconstruction consistently outperforms others. We highlight the utility of such a comparative approach for supernova or gravitational wave cosmological studies, where selecting an optimal peculiar velocity model is essential. Additionally, we present calibrated bulk flow curves predicted by the reconstructions and perform a density-velocity cross-correlation using a linear theory reconstruction to constrain the growth factor, yielding S-8 = 0.793 +/- 0.035. The result is in good agreement with both weak lensing and Planck, but is in strong disagreement with some peculiar velocity studies.

We study the stellar mass-iron metallicity relation of dwarf galaxies in the new high-resolution MEGATRON cosmological radiation-hydrodynamics simulations. These simulations model galaxy formation up to z≈8 in a region that will collapse into a Milky-Way-like galaxy at z=0, while self-consistently tracking Population III and II (Pop. III, Pop. II) star formation, feedback and chemical enrichment. MEGATRON dwarf galaxies are in excellent agreement with the observed stellar mass-metallicity relation at z=0, including an over-abundance of dwarfs along a flat plateau in metallicity (⟨ [Fe/H] ⟩≈ -2.5) at low stellar masses (M_⋆≤ 10^5 M_⊙). We tie this feature to the chemical enrichment of dwarf galaxies by Pop. III pair-instability supernova (PISN) explosions. The strong Lyman-Werner background (LW) from the protogalaxy ensures that PISNe occur in haloes massive enough (≈ 10^7 M_⊙) to retain their ejecta. We also predict a tail of ≈ 20% of iron-deficient (⟨ [Fe/H] ⟩≤ - 3) dwarf galaxies. We show that both plateau and tail (i) are robust to large variations in Pop. II feedback assumptions, and (ii) survive in bound satellites surrounding the central galaxy at z=0.

Supermassive black holes are prevalent at the centers of massive galaxies, and their masses scale with galaxy properties, increasing evidence suggesting that these trends continue to low stellar masses. Seeds are needed for supermassive black holes, especially at the highest redshifts explored by the James Webb Space Telescope. We study the hierarchical merging of galaxies via cosmological merger trees and argue that the seeds of supermassive black holes formed in nuclear star clusters via stellar black hole mergers at early epochs. Observable tracers include intermediate-mass black holes, nuclear star clusters, and early gas accretion in host dwarf galaxies, along with a potentially detectable stochastic gravitational-wave background, ejection of intermediate and supermassive black holes, and consequences of a significant population of early tidal disruption events and extreme mass ratio inspirals.

JWST observations are providing unprecedented constraints on the history of reionization owing to the ability to detect faint galaxies at z >> 6. Modelling this history requires understanding both the ionizing photon production rate (xi ion) and the fraction of those photons that escape into the intergalactic medium (f(esc)). Observational estimates of these quantities generally rely on spectroscopy for which large samples with well-defined selection functions remain limited. To overcome this challenge, we present and release a novel implicit likelihood inference pipeline, PHOTONIOn, trained on mock photometry to predict the escaped ionizing luminosity of individual galaxies ((N) over dot(ion)) based on photometric magnitudes and redshifts. We show that PHOTONIOn is able to reliably infer (N) over dotion from photometry. This is in contrast to traditional spectral energy distribution-fitting approaches which rely on f(esc) prescriptions that often overpredict (N) over dot(ion) for Lyman Continuum (LyC)-dim galaxies, even when given access to spectroscopic data. We have deployed PHOTONIOn on a sample of 4559 high-redshift galaxies from the JWST Advanced Deep Extragalactic Survey (JADES), finding gentle redshift evolutions of log10((N) over dot(ion))=(0.08 +/- 0.01)z+(51.60 +/- 0.06) and log(10)(f(esc)xi(ion))=(0.07 +/- 0.01)z+(24.12 +/- 0.07). Late-time values for the ionizing photon production rate density are consistent with both theoretical models and observations. Finally, we measure the evolution of the intergalactic medium ionized fraction to find that observed populations of star-forming galaxies are capable of driving reionization in this field to completion by z similar to 5.3 without the need for active galactic nucleus or other exotic sources, consistent with other studies of the same field. The 20 per cent of UV-brightest galaxies (M-UV<-18.5) reionize roughly 35 per cent of the survey volume, demonstrating that UV faint LyC emitters are crucial for reionization

Star formation is a key process that governs the baryon cycle within galaxies, however, the question of how it controls their growth remains elusive due to modeling uncertainties. To understand the impact of star formation models on galaxy evolution, we performed cosmological zoom-in radiation-hydrodynamic simulations of a dwarf dark matter halo, with a virial mass of M-vir similar to 10(9) M-circle dot at z = 6. We compared two different star formation models: a multi-freefall model combined with a local gravo-thermo-turbulent condition and a more self-consistent model based on a sink particle algorithm, where gas accretion and star formation are directly controlled by the gas kinematics. As the first study in this series, we used cosmological zoom-in simulations with different spatial resolutions and found that star formation is more bursty in the runs with the sink algorithm, generating stronger outflows than in the runs with the gravo-thermo-turbulent model. The main reason for the increased burstiness is that the gas accretion rates on the sinks are high enough to form stars on very short timescales, leading to more clustered star formation. As a result, the star-forming clumps are disrupted more quickly in the sink run due to more coherent radiation and supernova feedback. The difference in burstiness between the two star formation models becomes even more pronounced when the supernova explosion energy is artificially increased. Our results suggest that improving the modeling of star formation on small, sub-molecular cloud scales can significantly impact the global properties of simulated galaxies.

We use the cosmological hydrodynamical simulation NewHorizon to study the effects of the baryonic component on the inner mass profile of dark matter haloes of isolated galaxies (10(6)

We present three cosmological radiation-hydrodynamic zoom simulations of the progenitor of a Milky Way-mass galaxy from the MEGATRON suite. The simulations combine on-the-fly radiative transfer with a detailed non-equilibrium thermochemical network (81 ions and molecules), resolving the cold and warm gas in the circumgalactic medium (CGM) on spatial scales down to 20 pc and on average 200 pc at cosmic noon. Comparing our full non-equilibrium calculation with local radiation to traditional post-processed photoionization equilibrium (PIE) models assuming a uniform UV background (UVB), we find that non-equilibrium physics and local radiation fields fundamentally impact the thermochemistry of the CGM. Recombination lags and local radiation anisotropy shift ions away from their PIE+UVB values and modify covering fractions (for example, HI damped Lyα absorbers differ by up to 40

The vast amount of energy released by active galactic nuclei (AGN) is increasingly recognized as a key driver of evolution not only in massive galaxies and clusters, but also in low-mass dwarf galaxies. Despite this, their role in the early stages of galaxy formation and in self-regulating the rapid growth of the first and abundant supermassive black holes (SMBHs) remains poorly understood. Through new high-resolution zoom-in cosmological simulations, we follow the co-evolution of 10^5 M_⊙ black hole seeds with their host galaxy. The simulated suite progressively spans physics ranging from no AGN feedback and Eddington-limited thermal feedback, to more complex setups including non-Eddington-limited thermal, kinetic and radiative feedback. Across all our models, we find that black hole seeds efficiently reach masses of ∼10^7 M_⊙ by z=8. Although they exhibit notably different mass growth histories, these latter seem unimpeded by the presence of AGN feedback. The simulation including radiative feedback is the most distinct, with super-Eddington episodes driving fast and mass-loaded gas outflows (exceeding 2500 km s^-1) up to ∼50 kpc, along with minor stellar mass suppression in the host galaxy. Our measurements are in broad agreement with moderate luminosity quasars recently observed by JWST, producing overmassive black holes, dynamical masses of ∼10^9.5 M_⊙, and high, though short-lived, Eddington fraction accretion rates. These results advocate for a scenario where AGN feedback allows for rapid SMBH growth during the reionisation era, while driving winds that extend deep into the intergalactic medium - shaping host galaxies as well as more distant surroundings.

Cosmic ray (CR) feedback has been proposed as a powerful mechanism for driving warm gas outflows in galaxies. We use cosmological magnetohydrodynamic simulations to investigate the impact of CR feedback on neutral hydrogen (H i ) in a 10 ^11 M _⊙ dark matter halo at 2 < z < 4. To this end, we postprocess the simulations with ionizing radiative transfer and perform Monte Carlo Lyman- α (Ly α ) transfer calculations. CR feedback reduces H i column densities around young stars, thereby allowing more Ly α photons to escape and consequently offering a better match to the Ly α luminosities of observed Ly α emitters. Although galaxies with CR-driven outflows have more extended H i in the circumgalactic medium, two Ly α line properties sensitive to optical depth and gas kinematic—the location of the red peak relative to the Ly α line center in velocity space ( v _red ) and relative strength of the blue-to-red peaks ( B / R )—cannot distinguish between the CR-driven and non-CR simulations. This is because Ly α photons propagate preferentially along low H i density channels created by the ionizing radiation, thereby limiting the scattering with volume-filling H i . In contrast, the observed low flux ratios between the valley and peak and the surface brightness profiles are better reproduced in the model with CR-driven outflows because the Ly α photons interact more before escaping, rather than being destroyed by dust as is the case in the non-CR simulation. We discuss the potential cause of the paucity of sightlines in simulations that exhibit prominent red peaks and large v _red , which may require the presence of more volume-filling H i .

We present the MEGATRON suite of cosmological radiation hydrodynamics simulations following the formation of Milky Way-mass galaxies from the earliest cosmic epochs when Population III stars form to Cosmic Noon. The suite represents the first set of cosmological simulations that couples a vast non-equilibrium thermochemistry network of primordial species, metals, and molecules to multifrequency, on-the-fly radiation transport, allowing us to directly predict the spectral properties of early galaxies. By initializing the simulations at zero metallicity, resolving haloes well below the atomic cooling threshold, reaching parsec-scale resolution, and modeling a Milky Way-mass environment, we aim to address four key science themes: 1) Star formation at cosmic dawn, 2) Galaxy formation and the interstellar medium in the epoch of reionization, 3) The circumgalactic medium towards cosmic noon, and 4) Reionization in a local volume environment and near-field cosmology. In this introductory work, we present an overview of the physical characteristics of high-redshift MEGATRON galaxies and their environment at $z>8$. We present a library of $>175,000$ simulated galaxy spectra and demonstrate how the diversity of galaxy spectra seen by JWST is naturally reproduced in the context of a $Λ$CDM cosmology. This project represents a step towards making more direct comparisons between simulations and observations and will enable future work to both optimize methods for inferring galaxy properties from observations and to elucidate the physics that governs galaxy formation in the early Universe.

Recent observations by James Webb Space Telescope reveal an unexpectedly abundant population of rapidly growing supermassive black holes (SMBHs) in the early Universe, underscoring the need for improved models for their origin and growth. Employing new full radiative transfer hydrodynamical simulations of galaxy formation, we investigate the local and intergalactic feedback of SMBH progenitors for the Population III.1 (Pop III.1) scenario, i.e. efficient formation of supermassive stars from pristine, undisturbed dark matter minihaloes. Our cosmological simulations capture the R-type expansion phase of these Pop III.1 stars, with their H-ionizing photon luminosities of 10(53)s(-1) generating H II regions that extend deep into the intergalactic medium, reaching comoving radii of r(H II ) 1cMpc. We vary both the Pop III.1 ionization flux and cosmological formation environments, finding the former regulates their final r(H II), whereas the latter is more important in setting their formation redshift. We use the results from our radiation-hydrodynamics simulations to estimate the cosmic number density of SMBHs,nSMBH, expected from Pop III.1 progenitors. We find n(SMBH)similar to 10(-1)cMpc(-3), consistent with the results inferred from recent observations of the local and high-redshift universe. Overall, this establishes Pop III.1 progenitors as viable candidates for the formation of the first SMBH, and emphasizes the importance of exploring heavy mass seed scenarios.

Despite the vast amount of energy released by active galactic nuclei (AGNs), their role in early galaxy formation and in regulating the growth of supermassive black holes (SMBHs) remains poorly understood. Through new high-resolution zoom-in cosmological simulations, we follow the co-evolution of 10(5) M-circle dot black hole seeds with their host dwarf galaxy. We model ionizing feedback from a Pop III.1 progenitor, applicable to a wide range of internally or externally irradiated SMBH formation scenarios. The simulated suite progressively spans physics ranging from no AGN feedback to more complex setups including thermal, kinetic, and radiative feedback-explored for both low and enhanced AGN power. Across all our models, we find that black hole seeds efficiently reach masses of similar to 10(7) M-circle dot within a similar to 10(10) M-circle dot halo by z= 8. Although they exhibit notably different mass growth histories, these latter seem unimpeded by the presence of AGN feedback. The simulation including radiative feedback is the most distinct, with super-Eddington episodes driving fast and mass-loaded gas outflows (exceeding 2500 kms(1)) up to similar to 50 kpc, along with minor stellar mass suppression in the host galaxy. Our measurements are in broad agreement with moderate luminosity quasars recently observed by James Webb Space Telescope, producing overmassive black holes (SMBH-to-galaxy mass ratios 0.011), dynamical masses of similar to 10(9.5) M-circle dot, stellar masses of similar to 10(8.5) M-circle dot, and high, though short-lived, Eddington. fraction accretion rates. These results advocate for a scenario where AGN feedback allows for rapid SMBH growth during the reionization era, while driving winds that extend deep into the intergalactic medium-shaping host galaxies as well as more distant surroundings.

We introduce a new concept - termed 'planarity' - which aims to quantify planar structure in galaxy satellite systems without recourse to the number or thickness of planes. We use positions and velocities from the Gaia EDR3 to measure planarity in Milky Way (MW) satellites and the extent to which planes within the MW system are kinematically supported. We show that the position vectors of the MW satellites exhibit strong planarity but the velocity vectors do not, and that kinematic coherence cannot, therefore, be confirmed from current observational data. We then apply our methodology to NewHorizon, a high-resolution cosmological simulation, to compare satellite planarity in MW-like galaxies in a Lambda cold dark matter ($\rm {\Lambda CDM}$)-based model to that in the MW satellite data. We demonstrate that kinematically supported planes are common in the simulation and that the observed planarity of MW satellites is not in tension with the standard $\rm {\Lambda CDM}$ paradigm.

The scaling relations between the gas content and star formation rate of galaxies provide useful insights into the processes governing their formation and evolution. We investigated the emergence and the physical drivers of the global Kennicutt–Schmidt (KS) relation at 0.25 ≤ z ≤ 4 in the cosmological hydrodynamic simulation N EW H ORIZON , capturing the evolution of a few hundred galaxies with a resolution down to 34 pc. The details of this relation vary strongly with the stellar mass of galaxies and the redshift. A power-law relation Σ SFR ∝ Σ gas a with a ≈ 1.4, like that found empirically, emerges at z ≈ 2 − 3 for the more massive half of the galaxy population. However, no such convergence is found in the lower-mass galaxies, for which the relation gets shallower with decreasing redshift. At galactic scales, the star formation activity correlates with the level of turbulence of the interstellar medium, quantified by the Mach number, rather than with the gas fraction (neutral or molecular), confirming the conclusions found in previous works. With decreasing redshift, the number of outliers with short depletion times diminishes, reducing the scatter of the KS relation, while the overall population of galaxies shifts toward low densities. Our results, from parsec-scale star formation models calibrated with local Universe physics, demonstrate that the cosmological evolution of the environmental (e.g., mergers) and internal conditions (e.g., gas fractions) conspire to shape the KS relation. This is an illustration of how the interplay of global and local processes leaves a detectable imprint on galactic-scale observables and scaling relations.

The structure of magnetic fields in galaxies remains poorly constrained, despite the importance of magnetism in the evolution of galaxies. Radio synchrotron and far-infrared (FIR) polarization and polarimetric observations are the best methods to measure galactic scale properties of magnetic fields in galaxies beyond the Milky Way. We use synthetic polarimetric observations of a simulated galaxy to identify and quantify the regions, scales, and interstellar medium (ISM) phases probed at FIR and radio wavelengths. Our studied suite of magnetohydrodynamical cosmological zoom-in simulations features high-resolutions (10 pc full-cell size) and multiple magnetization models. Our synthetic observations have a striking resemblance to those of observed galaxies. We find that the total and polarized radio emission extends to approximately double the altitude above the galactic disk (half-intensity disk thickness of h _I radio ∼ h _PI radio = 0.23 ± 0.03 kpc) relative to the total FIR and polarized emission that are concentrated in the disk midplane ( h _I FIR ∼ h _PI FIR = 0.11 ± 0.01 kpc). Radio emission traces magnetic fields at scales of ≳300 pc, whereas FIR emission probes magnetic fields at the smallest scales of our simulations. These scales are comparable to our spatial resolution and well below the spatial resolution (<300 pc) of existing FIR polarimetric measurements. Finally, we confirm that synchrotron emission traces a combination of the warm neutral and cold neutral gas phases, whereas FIR emission follows the densest gas in the cold neutral phase in the simulation. These results are independent of the ISM magnetic field strength. The complementarity we measure between radio and FIR wavelengths motivates future multiwavelength polarimetric observations to advance our knowledge of extragalactic magnetism.

Astrophysical black holes (BHs) have two fundamental properties: mass and spin. While the mass-evolution of BHs has been extensively studied, much less work has been done on predicting the distribution of BH spins. In this paper, we present the spin evolution for a sample of intermediate-mass and massive BHs from the NewHorizon simulation, which evolved BH spin across cosmic time in a full cosmological context through gas accretion, BH-BH mergers and BH feedback including jet spindown. As BHs grow, their spin evolution alternates between being dominated by gas accretion and BH mergers. Massive BHs are generally highly spinning. Accounting for the spin energy extracted through the Blandford-Znajek mechanism increases the scatter in BH spins, especially in the mass range 10(5)-10(7)M(circle dot), where BHs had previously been predicted to be almost universally maximally spinning. We find no evidence for spin-down through efficient chaotic accretion. As a result of their high spin values, massive BHs have an average radiative efficiency of approximate to 0.19. As BHs spend much of their time at low redshift with a radiatively inefficient thick disc, BHs in our sample remain hard to observe. Different observational methods probe different sub-populations of BHs, significantly influencing the observed distribution of spins. Generally, X-ray-based methods and higher luminosity cuts increase the average observed BH spin. When taking BH spin evolution into account, BHs inject, on average, between three times (in quasar mode) and eight times (in radio mode) as much feedback energy into their host galaxy as previously assumed.