CoReCon: an open, community-powered collection of Reionization constraints

The number of available constraints on the Universe during and before cosmic reionization is rapidly growing. These are often scattered across inhomogeneous formats, unit systems and sampling strategies. In this paper, I introduce CoReCon, a Python package designed to provide a growing set of constraints on key physical quantities related to the Epoch of Reionization and a platform for the high-redshift research community to collect and store, in an open way, current and forthcoming observational constraints.Comment: Published in the Journal of Open Source Softwar

Dynamic Zoom Simulations: a fast, adaptive algorithm for simulating lightcones

The advent of a new generation of large-scale galaxy surveys is pushing cosmological numerical simulations in an uncharted territory. The simultaneous requirements of high resolution and very large volume pose serious technical challenges, due to their computational and data storage demand. In this paper, we present a novel approach dubbed Dynamic Zoom Simulations -- or DZS -- developed to tackle these issues. Our method is tailored to the production of lightcone outputs from N-body numerical simulations, which allow for a more efficient storage and post-processing compared to standard comoving snapshots, and more directly mimic the format of survey data. In DZS, the resolution of the simulation is dynamically decreased outside the lightcone surface, reducing the computational work load, while simultaneously preserving the accuracy inside the lightcone and the large-scale gravitational field. We show that our approach can achieve virtually identical results to traditional simulations at half of the computational cost for our largest box. We also forecast this speedup to increase up to a factor of 5 for larger and/or higher-resolution simulations. We assess the accuracy of the numerical integration by comparing pairs of identical simulations run with and without DZS. Deviations in the lightcone halo mass function, in the sky-projected lightcone, and in the 3D matter lightcone always remain below 0.1%. In summary, our results indicate that the DZS technique may provide a highly-valuable tool to address the technical challenges that will characterise the next generation of large-scale cosmological simulations.Comment: 17 pages, 13 figures, version accepted for publication in MNRA

Flows around galaxies I -- The dependency of galaxy connectivity on cosmic environments and effects on the star-formation rate

With the aim of bringing substantial insight to the fundamental question of how galaxies acquire their material for star-formation, we present the first comprehensive characterisation of the galaxy connectivity (i.e. the number of small-scale filamentary streams connected to a galaxy) in relation with the cosmic environment, and a statistical exploration of the impact of connectivity on the star-formation rate at z=2. We detect kpc-scale filaments directly connected to galaxies by applying the DisPerSE filament finder to the DM density around 2942 central galaxies ($M_* > 10^{8}$ $\mathrm{M}_\odot / h$) of the TNG50-1 simulation. Our results demonstrate that galaxy connectivity spans a broad range (from 0 to 9), with more than half of the galaxies connected to two or three streams. We examine a variety of factors that could influence the connectivity finding out that it increases with mass, decreases with local density for low mass galaxies, and does not depend on local environment, estimated by the Delaunay tessellation, for high mass galaxies. We further classify galaxies according to their location in different cosmic web environments, and we highlight the influence of the large-scale structure on the number of connected streams. Our results reflect the different strengths of the cosmic tides, which can prevent the formation of coherent streams feeding the galaxies, or even disconnect the galaxy from its local web. Finally, we show that, at fixed local density, the star-formation rate (SFR) of low mass galaxies is up to $5.9\sigma$ enhanced due to connectivity. This SFR boost is even more significant ($6.3\sigma$) for galaxies embedded in cosmic filaments, where the available matter reservoirs are large. A milder impact is found for high mass galaxies, hinting at different relative efficiencies of matter inflow via small-scale streams in galaxies of different masses.Comment: re-submitted version after positive referee report, comments welcom

SPICE: the connection between cosmic reionisation and stellar feedback in the first galaxies

We present SPICE, a new suite of RHD cosmological simulations targeting the epoch of reionisation. The goal of these simulations is to systematically probe a variety of stellar feedback models, including "bursty" and "smooth" forms of supernova energy injection, as well as poorly-explored scenarios such as hypernova explosions and radiation pressure. Subtle differences in the behaviour of supernova feedback drive profound differences in reionisation histories, with burstier forms of feedback causing earlier reionisation. We also find that some global galaxy properties, such as the dust-attenuated luminosity functions and star formation main sequence, remain degenerate between models. Stellar feedback and its strength determine the morphological mix of galaxies emerging by z = 5 and that the reionisation history is inextricably connected to intrinsic properties such as galaxy kinematics and morphology. While star-forming, massive disks are prevalent if supernova feedback is "smooth", "bursty" feedback preferentially generates dispersion-dominated systems. Different modes of feedback produce different strengths of outflows, altering the ISM/CGM in different ways, and in turn strongly affecting the escape of LyC photons. We establish a correlation between galaxy morphology and LyC escape fraction, revealing that dispersion-dominated systems have escape fractions 10-50 times higher than their rotation-dominated counterparts at all redshifts. Dispersion-dominated systems should thus preferentially generate large HII regions as compared to their rotation-dominated counterparts. Since dispersion-dominated systems are more prevalent if stellar feedback is more explosive, reionisation occurs earlier in our simulation with burstier feedback. Statistical samples of post-reionisation galaxy morphologies probed with JWST, ALMA and MUSE can constrain stellar feedback and models of cosmic reionisation

Bridging the Gap between Cosmic Dawn and Reionization favors Faint Galaxies-dominated Models

It has been claimed that traditional models struggle to explain the tentative detection of the 21\,cm absorption trough centered at $z\sim17$ measured by the EDGES collaboration. On the other hand, it has been shown that the EDGES results are consistent with an extrapolation of a declining UV luminosity density, following a simple power-law of deep Hubble Space Telescope observations of $4 < z < 9$ galaxies. We here explore the conditions by which the EDGES detection is consistent with current reionization and post-reionization observations, including the neutral hydrogen fraction at $z\sim6$--$8$, Thomson scattering optical depth, and ionizing emissivity at $z\sim5$. By coupling a physically motivated source model derived from radiative transfer hydrodynamic simulations of reionization to a Markov Chain Monte Carlo sampler, we find that it is entirely possible to reconcile the high-redshift (cosmic dawn) and low-redshift (reionization) existing constraints. In particular, we find that high contribution from low-mass halos along with high photon escape fractions are required to simultaneously reproduce cosmic dawn and reionization constraints. Our analysis further confirms that low-mass galaxies produce a flatter emissivity evolution, which leads to an earlier onset of reionization with gradual and longer duration, resulting in a higher optical depth. While our faint-galaxies dominated models successfully reproduce the measured globally averaged quantities over the first one billion years, they underestimate the late redshift-instantaneous measurements in efficiently star-forming and massive systems. We show that our (simple) physically-motivated semi-analytical prescription produces consistent results with the (sophisticated) state-of-the-art \thesan radiation-magneto-hydrodynamic simulation of reionization.Comment: 14 pages, 6 figures. Accepted for publication in ApJ. Comments are welcom

THESAN-HR: How does reionization impact early galaxy evolution?

Early galaxies were the radiation source for reionization, with the photoheating feedback from the reionization process expected to reduce the efficiency of star formation in low mass haloes. Hence, to fully understand reionization and galaxy formation, we must study their impact on each other. The THESAN project has so far aimed to study the impact of galaxy formation physics on reionization, but here we present the new THESAN simulations with a factor 50 higher resolution ($m_{\rm b} \approx 10^4$~M$_\odot$) that aim to self-consistently study the back-reaction of reionization on galaxies. By resolving haloes with virial temperatures $T_{\rm vir} < 10^4$~K, we are able to demonstrate that simplistic, spatially-uniform, reionization models are not sufficient to study early galaxy evolution. Comparing the self-consistent THESAN model (employing fully coupled radiation hydrodynamics) to a uniform UV background, we are able to show that galaxies in THESAN are predicted to be larger in physical extent (by a factor $\sim 2$), less metal enriched (by $\sim 0.2$~dex), and less abundant (by a factor $\sim 10$ at $M_{\rm 1500}~=~-10$) by $z=5$. We show that differences in star formation and enrichment patterns lead to significantly different predictions for star formation in low mass haloes, low-metallicity star formation, and even the occupation fraction of haloes. We posit that cosmological galaxy formation simulations aiming to study early galaxy formation $z \gtrsim 3$ must employ a spatially inhomogeneous UV background to accurately reproduce galaxy properties.Comment: Accepted for publication in MNRA

The THESAN project: Lyman-alpha emitter luminosity function calibration

The observability of Lyman-alpha emitting galaxies (LAEs) during the Epoch of Reionization can provide a sensitive probe of the evolving neutral hydrogen gas distribution, thus setting valuable constraints to distinguish different reionization models. In this study, we utilize the new THESAN suite of large-volume (95.5 cMpc) cosmological radiation-hydrodynamic simulations to directly model the Ly$\alpha$ emission from individual galaxies and the subsequent transmission through the intergalactic medium. THESAN combines the AREPO-RT radiation-hydrodynamic solver with the IllustrisTNG galaxy formation model and includes high- and medium-resolution simulations designed to investigate the impacts of halo-mass-dependent escape fractions, alternative dark matter models, and numerical convergence. We find important differences in the Ly$\alpha$ transmission based on reionization history, bubble morphology, frequency offset from line centre, and galaxy brightness. For a given global neutral fraction, Ly$\alpha$ transmission reduces when low mass haloes dominate reionization over high mass haloes. Furthermore, the variation across sightlines for a single galaxy is greater than the variation across all galaxies. This collectively affects the visibility of LAEs, directly impacting observed Ly$\alpha$ luminosity functions (LFs). We employ Gaussian Process Regression using SWIFTEmulator to rapidly constrain an empirical model for dust escape fractions and emergent spectral line profiles to match observed LFs. We find that dust strongly impacts the Ly$\alpha$ transmission and covering fractions of $M_{UV} 10^{11} {\rm M}_{\odot}$ haloes, such that the dominant mode of removing Ly$\alpha$ photons in non-LAEs changes from low IGM transmission to high dust absorption around $z \sim 7$.Comment: 20 pages, 18 figures, MNRAS, in press. Please visit www.thesan-project.com for more detail

The THESAN project: connecting ionized bubble sizes to their local environments during the Epoch of Reionization

An important characteristic of cosmic reionization is the growth of ionized gas bubbles surrounding early luminous objects. Understanding the connections between the formation and coalescence of these bubbles and their originating astrophysical sources is equally critical. We present results from a study of bubble sizes using the state-of-the-art THESAN radiation-hydrodynamics simulation suite, which self-consistently models radiation transport and realistic galaxy formation. We employ the mean-free path method, and track the evolution of the effective ionized bubble size at each point ($R_{\rm eff}$) throughout the Epoch of Reionization. We show there is a slow growth period for regions ionized early, but a rapid flash ionization process for regions ionized later as they immediately enter a large, pre-existing bubble. We also find that bright sources are preferentially in larger bubbles, and find consistency with recent observational constraints at $z \gtrsim 9$, but tension with idealized Lyman-alpha damping-wing models at $z \approx 7$ when the size distribution is complex. We find that high overdensity regions have larger characteristic bubble sizes, but the correlation decreases as reionization progresses, likely due to the runaway formation of large percolated bubbles. Finally, we compare the redshift at which a region transitions from neutral to ionized ($z_{\rm reion}$) with the time it takes to reach a given bubble size and conclude that $z_{\rm reion}$ is a reasonable local probe of small-scale bubble size statistics ($R_\text{eff} \lesssim 1$ cMpc). However, for larger bubbles, the correspondence between $z_{\rm reion}$ and size statistics weakens due to the time delay between the onset of reionization and the expansion of a large bubble, particularly at high redshifts.Comment: 14 pages, 15 figures. Comments welcome. Please visit https://www.thesan-project.com for more detail

The MillenniumTNG Project: The galaxy population at z≥8z\geq 8

The early release science results from $\textit{JWST}$ have yielded an unexpected abundance of high-redshift luminous galaxies that seems to be in tension with current theories of galaxy formation. However, it is currently difficult to draw definitive conclusions form these results as the sources have not yet been spectroscopically confirmed. It is in any case important to establish baseline predictions from current state-of-the-art galaxy formation models that can be compared and contrasted with these new measurements. In this work, we use the new large-volume ($L_\mathrm{box}\sim 740 \, \mathrm{cMpc}$) hydrodynamic simulation of the MillenniumTNG project, suitably scaled to match results from higher resolution - smaller volume simulations, to make predictions for the high-redshift ($z\gtrsim8$) galaxy population and compare them to recent $\textit{JWST}$ observations. We show that the simulated galaxy population is broadly consistent with observations until $z\sim10$. From $z\approx10-12$, the observations indicate a preference for a galaxy population that is largely dust-free, but is still consistent with the simulations. Beyond $z\gtrsim12$, however, our simulation results underpredict the abundance of luminous galaxies and their star-formation rates by almost an order of magnitude. This indicates either an incomplete understanding of the new $\textit{JWST}$ data or a need for more sophisticated galaxy formation models that account for additional physical processes such as Population~III stars, variable stellar initial mass functions, or even deviations from the standard $\Lambda$CDM model. We emphasise that any new process invoked to explain this tension should only significantly influence the galaxy population beyond $z\gtrsim10$, while leaving the successful galaxy formation predictions of the fiducial model intact below this redshift.Comment: Accepted for publication in MNRAS -- Part of the initial set of papers introducing the MillenniumTNG project. Visit www.mtng-project.org for more detail

The thesan project: public data release of radiation-hydrodynamic simulations matching reionization-era JWST observations

Cosmological simulations serve as invaluable tools for understanding the Universe. However, the technical complexity and substantial computational resources required to generate such simulations often limit their accessibility within the broader research community. Notable exceptions exist, but most are not suited for simultaneously studying the physics of galaxy formation and cosmic reionization during the first billion years of cosmic history. This is especially relevant now that a fleet of advanced observatories (e.g. James Webb Space Telescope, Nancy Grace Roman Space Telescope, SPHEREx, ELT, SKA) will soon provide an holistic picture of this defining epoch. To bridge this gap, we publicly release all simulation outputs and post-processing products generated within the THESAN simulation project at https://thesan-project.com. This project focuses on the $z \geq 5.5$ Universe, combining a radiation-hydrodynamics solver (AREPO-RT), a well-tested galaxy formation model (IllustrisTNG) and cosmic dust physics to provide a comprehensive view of the Epoch of Reionization. The THESAN suite includes 16 distinct simulations, each varying in volume, resolution, and underlying physical models. This paper outlines the unique features of these new simulations, the production and detailed format of the wide range of derived data products, and the process for data retrieval. Finally, as a case study, we compare our simulation data with a number of recent observations from the James Webb Space Telescope, affirming the accuracy and applicability of THESAN. The examples also serve as prototypes for how to utilise the released dataset to perform comparisons between predictions and observations.Comment: Data and documentation at https://www.thesan-project.com, comments and requests welcome, paper submitted to MNRA