TNG-Cluster & TNG300 Simulation Overview

• TNG-Cluster and TNG300 are advanced cosmological simulations using the AREPO code to model galaxy formation and cluster physics with high-resolution MHD techniques.
• They capture a wide range of scales from sub-L* galaxies to massive galaxy clusters, enabling detailed studies of feedback processes and the dynamics of the intracluster medium.
• The simulations provide robust comparisons with observations, offering insights into stellar mass functions, AGN feedback mechanisms, and X-ray properties of clusters.

The TNG-Cluster and TNG300 simulations are large-volume, high-resolution cosmological magnetohydrodynamical (MHD) simulations within the IllustrisTNG (“The Next Generation”) project. Designed to probe galaxy formation, large-scale structure, and intracluster medium physics, TNG-Cluster and TNG300 systematically extend the dynamic range, environmental sampling, and statistical power of modern cosmological simulations. These simulations have become foundational resources for theoretical and interpretive studies of galaxy clusters, cosmological baryons, and cosmic structure formation in the $\Lambda$CDM paradigm.

1. Simulation Overview and Scientific Objectives

TNG300 and TNG-Cluster share the objective of providing comprehensive, cosmological-volume realizations with sufficient mass and spatial resolution to resolve both large-scale structure and the internal evolution of massive halos, including galaxy clusters. TNG300 models a $(300\,\mathrm{Mpc})^3$ volume, yielding a statistically representative cosmic sample, while TNG-Cluster targets zoom-in realizations of particularly massive cluster halos within much larger parent boxes.

The scientific aims of both simulations include:

• Characterization of galaxy population statistics across environments
• Exploration of feedback processes (AGN, supernova) in high-mass halos
• Study of cluster assembly histories and ICM thermodynamics
• Examination of cosmic web topology and baryonic phases

2. Simulation Methodologies

Both suites employ the AREPO code, a moving-mesh finite-volume MHD solver, with gravity treated via a TreePM algorithm. The simulations implement a comprehensive physical model calibrated on smaller volume tests, incorporating:

• Radiative gas cooling and heating (primordial and metal-line, photoionization background)
• Star formation and ISM subgrid multiphase modeling
• Stellar evolution with chemical enrichment (nine individual elements tracked)
• Kinetic and thermal supernova feedback
• Dual-mode AGN feedback: thermal “quasar” and kinetic “radio” modes
• Magnetohydrodynamics with divergence control via Powell scheme
• Self-consistent cosmic magnetic field seeding and amplification

Resolution parameters are chosen to resolve sub-$L^*$ galaxies ($m_\mathrm{baryon}\sim10^{6-7}\,M_\odot$) while enabling simulation of large rare halos (clusters of $M_{200c} \gtrsim 10^{14-15}\,M_\odot$).

3. TNG300: Cosmological Volume Simulation

TNG300 models a uniform cube of $302.6\,\mathrm{Mpc}$ on a side, with $2\times2500^3$ resolution elements, achieving a dark matter particle mass of $m_\mathrm{DM}=5.9\times10^7\,M_\odot$ and an average baryonic cell mass of $1.1\times10^7\,M_\odot$. The gravitational softening length is $\epsilon=1.0\,\mathrm{kpc}$. The simulation adopts Planck cosmology parameters: $h=0.6774$, $\Omega_m=0.3089$, $\Omega_\Lambda=0.6911$, $\Omega_b=0.0486$, $\sigma_8=0.8159$, $n_s=0.9667$.

TNG300’s volume and resolution enable statistical studies of:

• Galaxy clusters (hundreds of $M_{200c}>10^{14}\,M_\odot$ halos)
• Cosmic variance in population and environmental trends
• Galaxy group and filamentary environment properties

4. TNG-Cluster: Zoom-in Cluster Simulations

TNG-Cluster uses multi-resolution zoom-in techniques to resimulate individual galaxy clusters identified in extremely large ($\gtrsim(1\,\mathrm{Gpc})^3$) dark-matter-only boxes. The high-resolution region contains the cluster and its immediate environment, preserving the correct tidal field. These zoom-ins reach similar or even finer baryonic mass and spatial resolutions as TNG300, while focusing computational resources on the formation and evolution of the ICM, BCGs, satellite galaxy populations, and intracluster stars.

This targeted approach allows:

• Detailed modeling of hydrostatic equilibrium, core entropy, and temperature profiles
• Analysis of AGN feedback-induced cavities, shocks, and turbulence
• High-fidelity comparisons to X-ray, SZ, and lensing observations
• Study of rare events such as cluster mergers and sloshing

5. Physical Results and Contributions

Both TNG300 and TNG-Cluster robustly reproduce a wide set of observed properties, including:

• Galaxy stellar mass functions and quenched fractions as a function of redshift and environment
• Mass–temperature and mass–X-ray luminosity relations for clusters
• ICM metallicity distributions and spatial gradients
• AGN feedback self-regulation and multiphase gas structure in massive halos
• Distribution and morphology of intracluster light (ICL) and stellar halos

TNG300 has enabled searches for environmental dependence in galaxy morphology and kinematics, while TNG-Cluster provides insight into baryonic processes at cluster scale, such as entropy cores, cooling flows, and AGN feedback modes.

6. Data Access, Community Use, and Limitations

Public data releases for both TNG300 and TNG-Cluster include full snapshots, halo catalogs with merger trees, emission mock outputs across multiple wavelengths, and derived statistics. The accessible database structure facilitates cross-comparison with observational surveys and detailed follow-up analyses.

Recognized limitations include:

• Absence of radiative transfer and non-ideal MHD effects
• Feedback model calibration primarily on galaxy-scale observables, with some tension in reproducing cluster core thermodynamics
• Resolution limits for the lowest-mass satellite galaxies and cold dense ISM phases
• Finite cosmic volume for TNG300 in rare object statistics; limited sample size for extreme clusters in TNG-Cluster

This suggests ongoing need for even larger-volume and higher-resolution runs to further probe the rarest objects and subtle baryonic phenomena.

7. Connections to Related Work and Future Directions

TNG300 and TNG-Cluster are successors to the original Illustris and contemporaneous with EAGLE, SIMBA, Magneticum, and other multi-physics cosmological suites. Current development trends, inspired by these results, include:

• Refinement of AGN feedback models, particularly kinetic/radio-mode implementations
• Inclusion of cosmic rays, dust physics, and multifluid ISM treatments
• Scaling up to $(1\,\mathrm{Gpc})^3$ full-physics simulations (“IllustrisTNG-1000” scale)
• Enhanced multi-wavelength synthetic survey pipelines
• Improved modeling of baryon–dark matter interplay on cluster and cosmic-web scales

A plausible implication is that joint exploitation of both large uniform volumes and focused zoom-ins, as exemplified by TNG300 and TNG-Cluster, will remain critical to bridging scales and confronting the full diversity of extragalactic astrophysical phenomena with theoretical predictions.