TNG300-1 Simulation Overview

• TNG300-1 simulation is a large-volume, high-resolution hydrodynamical model covering a 302.6 Mpc³ box with detailed galaxy formation physics.
• It quantifies star formation rate enhancements from galaxy interactions and mass assembly trends influenced by feedback and environment.
• The simulation probes cosmic web gas phases, void statistics, spin alignments, and intracluster light, offering robust comparisons with observations.

The TNG300-1 simulation is a large-volume, high-resolution cosmological hydrodynamical computation from the IllustrisTNG project. Encompassing a periodic box of (302.6 Mpc)$^3$ with baryonic resolution elements of $\sim1.1 \times 10^7\,M_\odot$, TNG300-1 serves as a statistically powerful platform for investigating galaxy population statistics, baryonic structure formation, cosmic web gas phases, cluster dynamics, and environmental effects. Its scale enables the resolution of both rare, high-mass structures (including massive galaxy clusters and superclusters) and the systematic study of all major baryonic and dark matter components over cosmological time.

1. Fundamental Simulation Characteristics and Physics

TNG300-1 evolves $2 \times 2500^3$ particles (dark matter and baryons) in a comoving cube of 302.6 Mpc per side, employing the AREPO moving-mesh code. Its adopted cosmological parameters [$\Omega_m = 0.3089$, $\Omega_\Lambda = 0.6911$, $\Omega_b = 0.0486$, $h = 0.6774$, $\sigma_8 = 0.8159$, $n_s = 0.9667$] reflect Planck results (Montenegro-Taborda et al., 2023). Baryonic and dark matter mass elements are evolved alongside robust galaxy formation physics: metal-dependent cooling, star formation, kinetic and thermal supermassive black hole (SMBH) feedback, galactic winds, and chemical enrichment (Montenegro-Taborda et al., 2023, Galárraga-Espinosa et al., 2020). Stellar and black hole particles are tracked, mergers are resolved, and feedback is injected according to subgrid prescriptions validated in TNG100-1, but executed at lower spatial (and mass) resolution, trading detail for statistical power.

2. Galaxy Interactions and Star Formation Triggering

A central result from TNG300-1 is the quantification of specific star formation rate (sSFR) enhancement in massive galaxies $(M_*\!>\!10^{10}\,M_\odot)$ as a function of proximity to companions (Patton et al., 2020, Brown et al., 2023). Using matched control samples and robust pair selection ($0.1<\mu<10$), the enhancement ratio

$$Q(\mathrm{sSFR}) = \frac{\langle \mathrm{sSFR}_{\mathrm{hosts}} \rangle}{\langle \mathrm{sSFR}_{\mathrm{controls}} \rangle}$$

is statistically significant ($Q>1$ at $2\sigma$) out to 280 kpc (3D) and 260 kpc (projected); at the crowding limit ($r\sim17.4$ kpc), $Q\approx1.72\pm0.02$. Interactions with star-forming companions produce pronounced sSFR boosts reaching $Q\approx2.27\pm0.06$ ($\sim\!2\times$ enhancement), while passive companions can induce mild suppression ($Q\approx0.88$) at intermediate separations (Brown et al., 2023). Notably, these effects persist out to 300–350 kpc, indicating that both direct and indirect gravitationally induced gas inflows operate efficiently in the hierarchical assembly regime.

Comparisons to TNG100-1 (higher resolution) show somewhat stronger enhancements, while EAGLE and Illustris-1 exhibit amplitudes nearly half as large, emphasizing the role of feedback modeling and resolution (Patton et al., 2020). Redshift evolution is moderate—enhancements slightly weaken as $z$ increases, in accord with the declining cosmic star formation density.

3. Stellar Mass Assembly and Role of Feedback

Analysis of TNG300-1 central galaxies ($M_* \gtrsim 10^{9.5}\,M_\odot$, $M_{\rm halo}\!>\!10^{12}\,M_\odot$) reveals that both “downsizing” and halo mass dependence are robustly reproduced: higher $M_*$ galaxies (at fixed $M_{\rm halo}$) have older mass-weighted assembly times; at fixed $M_*$, higher halo mass systems are somewhat younger, likely due to prolonged gas accretion (Jackson et al., 2020). Growth epochs (e.g., lookback times $t_{10}$, $t_{50}$, $t_{90}$) span $10$–$2$ Gyr, capturing the bulk and 90% assembly phases.

TNG300-1 exhibits discrepancies at intermediate $M_* \sim 10^{11}\,M_\odot$, overpredicting assembly times by $\sim$2–3 Gyr relative to SDSS. This deviation tracks regions with excess quenched fractions, attributed to the kinetic AGN feedback mechanism, which triggers strong, early quenching in galaxies near the $M_* \sim 10^{10.5}\,M_\odot$/$M_{\rm halo} \sim 10^{12.5}\,M_\odot$ transition (Jackson et al., 2020). Thus, TNG300-1 validates general mass assembly trends but exposes the sensitivity of stellar buildup timescales to feedback models and their critical mass thresholds.

4. Cosmic Web, Filament Gas Phases, and Void Statistics

Full cosmological coverage enables the TNG300-1 simulation to dissect gas-phase structure in cosmic filaments (Galárraga-Espinosa et al., 2020) and voids (Rodríguez-Medrano et al., 2023, Curtis et al., 2024, Curtis et al., 22 Apr 2025). Filaments at $z=0$ are dominated by warm–hot intergalactic medium (WHIM; $T=10^5{-}10^7$ K), comprising $\gtrsim80\%$ of baryons at $r\sim1$ Mpc from the spine. Pressure and temperature radial profiles are nearly isothermal out to $r\sim1.5$ Mpc with $T_{\rm core}=4$–$13 \times 10^5$ K, $P_{\rm core}=4$–$12 \times 10^{-7}$ keV/cm$^3$—values orders of magnitude below cluster centers. The Sunyaev–Zel'dovich signal from filament cores lies in $y\sim0.5$–$4.1 \times10^{-8}$, compatible with Planck and related observations (Galárraga-Espinosa et al., 2020).

Void studies find that void regions are more depleted in luminous galaxies (density contrast $\Delta\sim-0.77$) than in dark matter ($\Delta\sim-0.64$) (Curtis et al., 2024, Curtis et al., 22 Apr 2025). Radial profiles are nearly inverse-top-hat, with “void-in-cloud” and “void-in-void” distinctions reflecting the embedding cosmic environment. Importantly, a linear relationship between galaxy and dark matter underdensity is present inside voids, with the slope matching the cosmological galaxy bias. Over time, dark matter profiles in voids become progressively more underdense in the core and more overdense at the ridge, whereas galaxy profiles saturate with fully evacuated centers already at high redshift (Curtis et al., 22 Apr 2025).

Void galaxies display higher sSFR ($\sim$20% above field values), are younger, less massive, bluer, metal-poorer, and smaller than non-void counterparts (Rodríguez-Medrano et al., 2023, Curtis et al., 2024). This environmental dependence, including the prevalence of delayed, late-time mergers and high accreted stellar mass fractions in low-mass void satellites, challenges the notion that void galaxies are strictly isolated and passively evolving.

5. Galaxy Spin Alignment and Large-Scale Structure

Statistical analysis of TNG300-1 demonstrates strong perpendicular alignment of galaxy group spins with their nearest filament axes, predominantly affecting more massive groups and those located closer to filaments (Wang et al., 28 Aug 2025). The spin–filament misalignment angle averages $\sim\!59^\circ$, exceeding the expectation for random orientation ($\sim\!57.3^\circ$). This perpendicular alignment is robust to changes in group richness, member selection threshold, and redshift. By contrast, using galaxy members instead of dark matter particles to trace group spins introduces a systematic $\sim\!38^\circ$ bias in the measured orientation, independent of tracer selection—highlighting an intrinsic limitation when comparing theoretical predictions and observations.

Galaxy spin alignment around voids follows a distinct regime: high-mass, high-spin, low-velocity galaxies near the void shell ($0.9$–$1.4\,R_{\rm void}$) show strong ($>9\sigma$) perpendicular alignment to the void–center direction (Dávila-Kurbán et al., 2022). This signal is insensitive to local density but highly sensitive to void-centric radial velocity, and may complicate interpretations of weak lensing in future large-scale surveys.

6. Intracluster Light, BCG Assembly, and Cluster Structure

TNG300-1’s volume enables systematic study of clusters and their diffuse components. The brightest cluster galaxies (BCGs) assemble most of their mass ex situ—about 70% in the BCG proper (within 30 kpc), 80% in BCG+ICL (intracluster light), and 90% in the diffuse ICL (Montenegro-Taborda et al., 2023). Ex situ (accreted) stars dominate BCGs at all radii in massive clusters, with major merger remnants deposited in the center and tidally stripped material populating the outskirts. BCGs typically undergo $\sim$2–3 major mergers since $z=1$–2, with half of the $z=0$ stellar mass having formed by $z\sim3$ but only assembled to the final BCG by $z\sim0.8$–$0.5$. The resulting cluster stellar profiles show good overall agreement with observations in mass and SFR, though certain photometric properties (e.g., more extended BCG+ICL radii and brighter surface brightness profiles by $0.4$–$1$ mag/arcsec$^2$) deviate, potentially reflecting over-efficient tidal disruption or limits of feedback implementation (Montenegro-Taborda et al., 2 Jul 2025).

Quantitative comparison of intracluster light (ICL) in TNG300-1 with wide-field imaging finds median ICL fractions $f_{\rm ICL}\sim0.3$–$0.35$, consistent across multiple SB/morphological definitions. Systematic offsets in size and luminosity are observed, but the relative ICL/BCG partition agrees when identical analysis pipelines are used (Montenegro-Taborda et al., 2 Jul 2025).

The spatial morphology of the BCG+ICL trace the projected dark matter distribution with high fidelity, as quantified by the Weighted Overlap Coefficient ($\mathrm{WOC}\gtrsim0.85$), especially in dynamically relaxed clusters. This “light traces mass” relation is robust for BCG+ICL and gas, but not for member galaxies, which serve as better mass tracers only at larger cluster-centric radii or in richer clusters (Yoo et al., 19 Jun 2025). Clusters forming earlier (higher assembly redshift) and with larger BCG-to-second-brightest magnitude gaps show the greatest BCG+ICL–DM spatial coincidence.

7. Limitations, Model Dependencies, and Future Directions

TNG300-1 exhibits subtle but important mismatches with observations and higher-resolution simulations. For instance, kinetic AGN feedback leads to prematurely old assembly times for intermediate-mass galaxies (Jackson et al., 2020), and satellite disruption appears overly efficient (overextending BCG+ICL light profiles and altering satellite abundances) (Alonso et al., 2022, Montenegro-Taborda et al., 2 Jul 2025). Large-scale environmental effects, such as “two-halo conformity” and backsplash phenomena, are robust and more pronounced than in some semi-analytic models, largely due to a significant fraction of low-mass centrals that were previously satellites (so-called “former satellites”) and which dominate the environmental imprint on the quenched population close to massive halos (Palma et al., 2024).

The vast TNG300-1 cosmological volume empowers statistically rigorous studies of rare objects (massive clusters, voids, superclusters) and ensemble-level environmental processes, but its finite (albeit high) resolution results in lower central densities, stronger satellite disruption, and potentially altered accretion/stripping histories compared to TNG100-1 or TNG-Cluster.

The simulation’s design—including physical subgrid modeling, feedback threshold choices, and cosmological parameters—directly affects key observable predictions (e.g., the AGN–stellar mass relation, ICL profiles, void statistics). These dependencies are evident when contrasting to observations and when comparing to targeted high-resolution cluster “zoom-ins” (Nelson et al., 2023, Lee et al., 2023) or alternative hydrodynamical runs.

Table: Key Measurable Properties in TNG300-1 (Selected Results)

Observable/Statistic	Value / Trend (TNG300-1)	Context / Comments
$Q(\mathrm{sSFR})$ at 17 kpc	$1.72\pm0.02$ (all pairs)	sSFR enhancement ratio (Patton et al., 2020)
$Q(\mathrm{sSFR})$ (SFG pairs)	$2.27\pm0.06$	Star-forming companions (Brown et al., 2023)
$Q(\mathrm{sSFR})$ (Passive)	$0.88\pm0.01$ @ 200 kpc	Suppression; passive companions (Brown et al., 2023)
Ex situ fraction (BCG)	$\sim70\%$	Within 30 kpc (Montenegro-Taborda et al., 2023)
$\Delta(\mathrm{void~center})$	$-0.77\pm0.04$ (galaxies), $-0.64\pm0.02$ (DM)	$z=0$; mass–light decoupling (Curtis et al., 2024)
Spin–Filament Angle	$\langle\theta\rangle\approx59.07^\circ$	Robust perpendicular trend (Wang et al., 28 Aug 2025)
ICL Fraction, $f_{\rm ICL}$	$\sim0.3$ (median)	All methods, agrees with obs. (Montenegro-Taborda et al., 2 Jul 2025)

Summary

TNG300-1 is a foundational resource for precision studies of galaxy populations, star formation triggering, structure assembly, cosmic web gas and voids, and cluster morphology at the $\gtrsim$Mpc scale. It provides strong constraints on the interplay between galactic processes and cosmic environment, yielding results that are broadly concordant with observations but exposing the critical dependence on feedback physics, subgrid models, and resolution. The simulation’s statistical power, multi-component outputs, and broad spatial coverage ensure its ongoing utility in both theory and the interpretation of upcoming spectroscopic and imaging surveys.