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

Enrico Garaldi, Rahul Kannan+14 more|arXiv (Cornell University)|Sep 12, 2023

Astronomy and Astrophysical ResearchPhysics and Astronomy3 citations

TL;DR

The thesan project releases a comprehensive suite of radiation-hydrodynamic simulations spanning z ≥ 5.5, combining the arepo-rt radiation transport code with the IllustrisTNG galaxy formation model and dust physics to model the Epoch of Reionization. It provides high-resolution, publicly accessible data products—including high-cadence Cartesian outputs and post-processed catalogs—demonstrating strong agreement with recent James Webb Space Telescope observations of high-redshift galaxies, including key scaling relations like the main sequence and mass–metallicity relation.

ABSTRACT

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.

Motivation & Objective

• To address the lack of publicly available, high-fidelity cosmological simulations that simultaneously model galaxy formation and cosmic reionization during the first billion years of cosmic history.
• To overcome the technical and computational barriers limiting broad community access to state-of-the-art radiation-hydrodynamic simulations of the high-redshift Universe.
• To provide a comprehensive, publicly accessible dataset that enables direct comparison between theoretical predictions and upcoming multi-wavelength observations from JWST, Roman Space Telescope, and other next-generation facilities.
• To support the scientific community with rich, well-documented data products—including high-time-cadence outputs and post-processed catalogs—optimized for analysis with widely used tools.
• To establish a foundation for ongoing, community-driven research by enabling future expansions in volume, resolution, and physical modeling, including zoom-in and reionization-history-resolved simulations.

Proposed method

• The project employs the arepo-rt code to self-consistently simulate radiation transport in a cosmological volume, capturing the inhomogeneous ionizing radiation field from early sources.
• It integrates the well-validated IllustrisTNG galaxy formation model, including feedback from stars and black holes, and includes cosmic dust physics to improve realism.
• The simulations are run across 16 distinct configurations varying in volume (from 100 to 1000 Mpc/h), resolution (up to 20 pc), and physical subgrid models, enabling systematic study of physical uncertainties.
• High-cadence Cartesian outputs are generated to track the time evolution of key physical quantities at fine temporal resolution, enabling detailed temporal analysis of reionization processes.
• A wide array of post-processing products—including group catalogs, star formation histories, and synthetic photometry—are produced and made publicly available via the project’s website.
• The data are integrated with widely used scientific software (e.g., Python-based tools like numpy, matplotlib, and custom analysis packages) to lower the barrier to entry for researchers of all expertise levels.

Experimental results

Research questions

• RQ1 How well do radiation-hydrodynamic simulations including full radiation transport reproduce observed properties of high-redshift galaxies at z ≥ 6?
• RQ2 What is the impact of varying physical models—such as feedback prescriptions, resolution, and volume—on the predicted properties of galaxies during the Epoch of Reionization?
• RQ3 To what extent can the simulated galaxy population match key observational scaling relations such as the main sequence of star formation, the mass–metallicity relation, and the UV slope–stellar mass relation?
• RQ4 How does the fraction of dust-obscured star formation vary with galaxy mass at z ≥ 6, and what does this imply for observational selection effects in early-universe surveys?
• RQ5 What are the effects of local reionization history and environmental overdensity on the structural and star formation properties of individual galaxies in high-redshift simulations?

Key findings

• The thesan simulations successfully reproduce key observational scaling relations at z ≥ 6, including the galaxy main sequence, the mass–metallicity relation, and the UV slope–stellar mass relation, demonstrating strong consistency with recent JWST data.
• The simulations predict a non-negligible fraction of dust-obscured star formation, with the fraction increasing with galaxy stellar mass, suggesting that dust extinction may significantly affect observed UV luminosities at high redshift.
• The high-cadence Cartesian outputs reveal detailed, time-resolved evolution of ionization fronts and star formation, enabling the study of reionization as a dynamic, patchy process rather than a global transition.
• The simulations show that the reionization process is highly sensitive to local physics, including feedback and radiation transport, with significant variations in ionization structure and galaxy properties across different simulation variants.
• The project’s data release includes 16 distinct simulation runs with varying volumes, resolutions, and physical models, enabling systematic exploration of uncertainties in early galaxy formation physics.
• The integration of thesan data into standard analysis tools and the availability of comprehensive documentation significantly lower the barrier to entry for researchers without high-performance computing expertise.