Jiutian-300: High-Res Cosmological Simulation

• Jiutian-300 is a large-scale dark-matter-only cosmological N-body simulation with a 300 h⁻¹Mpc volume and 6144³ particles, offering exceptional mass resolution for subhalo studies.
• It employs dual subhalo pipelines, including SUBFIND and HBT+, to generate robust halo catalogs and merger trees essential for analyzing structure formation.
• Jiutian-300 underpins applications from reionization and 21-cm signal modeling to mock galaxy catalog construction, advancing precision cosmology research.

Searching arXiv for Jiutian-300 and closely related Jiutian simulation papers. Jiutian-300 is a large cosmological $N$-body simulation within the broader Jiutian simulation suite developed for the China Space Survey Telescope (CSST) extragalactic surveys. In the primary-run taxonomy of the suite, it is the $300\,h^{-1}\mathrm{Mpc}$, $6144^3$-particle realization under the fiducial Planck 2018 $\Lambda$CDM cosmology, designed to combine high mass resolution with sufficient volume for halo, subhalo, galaxy-formation, and reionization studies (Han et al., 27 Mar 2025). Across recent work, Jiutian-300 functions both as a standalone dark-matter backbone for structure-formation analyses and as an input to downstream pipelines including merger-tree construction, semi-analytic galaxy modeling, mock light-cone generation, and post-processed radiative-transfer calculations for Epoch of Reionization observables (Tan et al., 5 Nov 2025, Ma et al., 10 Mar 2026).

1. Position within the Jiutian simulation suite

The Jiutian simulations are organized as a hybrid suite with four complementary modules: primary runs, emulator runs, reconstruction runs, and extension runs (Han et al., 27 Mar 2025). Jiutian-300 belongs to the primary runs, whose role is to provide high-resolution, large-volume $N$-body predictions under the fiducial concordance cosmology and to serve as the basis for halo/subhalo catalogs, merger trees, and mock galaxy catalogs.

Within the primary runs, three box sizes are specified: Jiutian-300, Jiutian-1G, and Jiutian-2G, each with $6144^3$ particles (Han et al., 27 Mar 2025). Jiutian-300 is the smallest-volume and highest-mass-resolution member of this trio, with mass resolution up to $1.0 \times 10^7\,h^{-1} M_\odot$ (Han et al., 27 Mar 2025). This places it in a distinct niche relative to Jiutian-1G and Jiutian-2G: it sacrifices survey-scale volume in exchange for improved access to low-mass halo and subhalo structure.

A plausible implication is that Jiutian-300 is the preferred primary run when the scientific priority is substructure fidelity or high-redshift source modeling rather than maximal cosmological volume. That inference is consistent with its use in convergence studies of subhalo populations (Xu, 11 Aug 2025) and in reionization calculations that require resolved low-mass halos (Ma et al., 10 Mar 2026).

2. Numerical specification and cosmological setup

Jiutian-300 is described as a dark matter-only cosmological $N$-body simulation with box size $L = 300\,h^{-1}\mathrm{Mpc}$ and particle number $N_p = 6144^3 = 231{,}928{,}233{,}984$ (Xu, 11 Aug 2025). Its particle mass is given as $300\,h^{-1}\mathrm{Mpc}$0 (Xu, 11 Aug 2025), consistent with the suite-level statement that the primary runs reach mass resolution up to $300\,h^{-1}\mathrm{Mpc}$1 (Han et al., 27 Mar 2025).

The simulation adopts Planck 2018 cosmological parameters,

$300\,h^{-1}\mathrm{Mpc}$2

as reported in reionization and suite-overview work (Ma et al., 10 Mar 2026, Han et al., 27 Mar 2025). It starts at $300\,h^{-1}\mathrm{Mpc}$3, ends at $300\,h^{-1}\mathrm{Mpc}$4, and has 128 snapshot outputs; in the reionization application, 39 snapshots with $300\,h^{-1}\mathrm{Mpc}$5 are used (Ma et al., 10 Mar 2026). The primary runs are also described as having high time-resolution snapshots and on-the-fly particle lightcones (Han et al., 27 Mar 2025).

Two different code attributions appear in the supplied literature. The reionization study specifies Gadget-4 as the simulation code for Jiutian-300 (Ma et al., 10 Mar 2026), whereas the subhalo-convergence study describes Jiutian-300 as run with GADGET-3/4 (Xu, 11 Aug 2025). Since both formulations are present in the source material, the safest characterization is that Jiutian-300 is a GADGET-family dark-matter-only simulation.

3. Halo finding, subhalo tracking, and merger trees

A central feature of the Jiutian primary runs is the use of two independent subhalo and merger-tree pipelines: SubFind+LHaloTrees and HBT+ (Han et al., 27 Mar 2025). For Jiutian-300 specifically, the reionization study reports halo identification with the Friend-of-Friend (FoF) algorithm and subhalo identification with SUBFIND (Ma et al., 10 Mar 2026), while the subhalo-distribution analysis uses HBT+ catalogs (Xu, 11 Aug 2025). This dual-pipeline strategy is an explicit design feature of the broader suite (Han et al., 27 Mar 2025).

In the reionization application, the minimum halo mass resolved is $300\,h^{-1}\mathrm{Mpc}$6, corresponding to 20 particles (Ma et al., 10 Mar 2026). In the HBT+-based analyses across the Jiutian suite, subhalos with more than 20 dark matter particles are treated as resolved objects, and the time-domain tracking of HBT+ is emphasized for its handling of subhalo hierarchy, mergers, and persistent identity (Tan et al., 5 Nov 2025, Han et al., 27 Mar 2025). The mock-catalog work based on Jiutian-1G further notes that HBT+ resolves ambiguities such as central/satellite flip-flopping and fragmentations and tracks orphan galaxies when subhalos are disrupted (Tan et al., 5 Nov 2025). This suggests analogous methodological advantages whenever HBT+ products from Jiutian-300 are employed.

The suite overview highlights one specific scientific result enabled by these tree constructions: the subhalo peak mass functions of different levels are approximately universal (Han et al., 27 Mar 2025). For the level-1 subhalo peak mass function,

$300\,h^{-1}\mathrm{Mpc}$7

with $300\,h^{-1}\mathrm{Mpc}$8, and higher-level peak mass functions can be built through self-convolutions,

$300\,h^{-1}\mathrm{Mpc}$9

The paper states that this universality extends down to subhalo-to-host mass ratios of approximately $6144^3$0 (Han et al., 27 Mar 2025).

4. Role in galaxy-population and mock-catalog construction

Jiutian-300 is part of a simulation environment whose high-level products include mock galaxy catalogs, lensing maps and catalogs, mock images, and emission-line galaxy catalogs (Han et al., 27 Mar 2025). The suite overview states that, on top of the primary runs, four sets of mock galaxy light-cone catalogs are produced from semi-analytical models and subhalo abundance matching, with observational properties including galaxy SED, emission lines, lensing distortions, and mock images (Han et al., 27 Mar 2025).

Although the detailed mock-catalog construction in the supplied material is centered on Jiutian-1G rather than Jiutian-300, the relevant methodology clarifies how Jiutian primary runs are generally used. Merger trees extracted from the simulations are coupled to the GAEA semi-analytical model of galaxy formation, and spectral energy distributions are generated with StarDuster, a neural-network-based stellar population synthesizer trained on radiative-transfer simulations (Tan et al., 5 Nov 2025). Galaxy light-cones up to $6144^3$1 are then generated with BLiC, which interpolates galaxy properties over time using an optimized interpolation scheme (Tan et al., 5 Nov 2025).

In this pipeline, the comoving-distance condition for placing galaxies on the light cone is

$6144^3$2

For the SED modeling, StarDuster uses FSPS with a Chabrier (2003) IMF, includes geometry-aware dust attenuation, and adopts

$6144^3$3

for the dust mass based on cold-gas metal mass (Tan et al., 5 Nov 2025).

The supplied sources do not state that Jiutian-300 itself is the run used for the CSST extragalactic light-cone product described in (Tan et al., 5 Nov 2025); that paper instead identifies Jiutian-1G as the flagship run for balancing resolution and volume. However, because Jiutian-300 is one of the primary runs that supply halo, subhalo, and merger-tree products (Han et al., 27 Mar 2025), a plausible implication is that it serves as a higher-resolution complement for problems where lower-mass structure is especially important.

5. Jiutian-300 in reionization and 21-cm signal modeling

A major scientific use of Jiutian-300 is in modeling the Epoch of Reionization (EoR) and the associated 21-cm signal (Ma et al., 10 Mar 2026). In that workflow, Jiutian-300 supplies the underlying density field and halo catalogs, which are coupled to the semi-analytic model L-Galaxies 2020 to generate galaxy catalogs with star-formation histories, stellar masses, metallicities, and related properties (Ma et al., 10 Mar 2026).

The resulting galaxy catalog is then post-processed with the one-dimensional radiative-transfer code Grizzly, which models the ionization and heating of the intergalactic medium and computes the 21-cm observables (Ma et al., 10 Mar 2026). The dark-matter density field from Jiutian-300 is mapped onto a $6144^3$4 grid with cell width $6144^3$5, and the dark-matter density is used as a proxy for the IGM gas density in each cell (Ma et al., 10 Mar 2026).

The differential 21-cm brightness temperature is given in the study as

$6144^3$6

where $6144^3$7 comes from the Jiutian-300 density field, $6144^3$8 from Grizzly, and $6144^3$9 is assumed equal to the kinetic temperature $\Lambda$0 for $\Lambda$1 (Ma et al., 10 Mar 2026). The 21-cm power spectrum is

$\Lambda$2

The reionization study reports that ionized regions produced by galaxies with star-formation histories derived from L-Galaxies 2020 are slightly larger and warmer than those obtained with a constant star-formation rate, and that, for a fixed stellar mass, galaxies produce smaller ionized regions with increasing stellar-mass-weighted stellar age $\Lambda$3 (Ma et al., 10 Mar 2026). The paper concludes that different models of galactic star-formation history affect the gas heating and ionizing processes during the EoR and consequently the 21-cm global signal and power spectrum (Ma et al., 10 Mar 2026). In this context, Jiutian-300 is not merely a background density realization; it is the spatial framework that fixes the topology of recombination, bubble growth, and heating.

6. Numerical convergence, orphan modeling, and limits of interpretation

Jiutian-300 is also used as a high-resolution benchmark for subhalo abundance and phase-space studies (Xu, 11 Aug 2025). In that analysis, Jiutian-300 is compared with Jiutian-1G, which has the same particle count but lower mass resolution, in order to determine which subhalo statistics are numerically converged and how far orphan-based corrections can extend their reliability.

The main result is that the surviving subhalo peak mass function converges only for subhalos with peak mass $\Lambda$4 above 5000 particles (Xu, 11 Aug 2025). For Jiutian-300, this corresponds to $\Lambda$5 (Xu, 11 Aug 2025). Below that threshold, numerical disruption becomes significant. The study further reports that including orphan subhalos, with survival determined using the merger-timescale model of Jiang et al., accurately recovers the peak-mass function and outperforms other tested models (Xu, 11 Aug 2025).

The merger-timescale model is written as

$\Lambda$6

and the empirically fitted surviving subhalo peak mass function takes a double-Schechter form,

$\Lambda$7

with $\Lambda$8 (Xu, 11 Aug 2025).

Including orphans allows recovery of the real-space spatial and velocity distributions to $\Lambda$9--$N$0 accuracy down to scales of $N$1--$N$2 (Xu, 11 Aug 2025). However, convergence below $N$3 remains difficult, and the paper attributes residual discrepancies partly to cosmic variance and finite-box effects in the smaller Jiutian-300 simulation (Xu, 11 Aug 2025). The study also emphasizes that redshift-space multipoles are more difficult to recover than real-space statistics because poorly resolved close pairs in real space contaminate much larger scales through Fingers-of-God distortions (Xu, 11 Aug 2025). It therefore recommends modified or alternative redshift-space measures that reduce sensitivity to small projected separations.

This evidence is important for interpreting Jiutian-300 outputs. The simulation is high resolution by the standards of large cosmological boxes, but the literature explicitly cautions against uncritical use of its inner-halo subhalo phase space and small-scale redshift-space clustering (Xu, 11 Aug 2025).

7. Scientific significance, accessibility, and nomenclature

Within the Jiutian program, Jiutian-300 occupies the intersection of three methodological priorities: high-resolution dark-matter dynamics, compatibility with multiple subhalo/tree pipelines, and downstream interoperability with semi-analytic and radiative-transfer frameworks (Han et al., 27 Mar 2025, Ma et al., 10 Mar 2026). Its scientific use cases therefore span galaxy-halo connection modeling, subhalo statistics, mock-data generation, and EoR signal prediction.

The suite as a whole provides low-level products such as particle snapshots, particle lightcones, halo/subhalo catalogs, and merger trees, as well as high-level products including multiple mock galaxy catalogs, lensing products, mock images, and constrained-realization datasets (Han et al., 27 Mar 2025). The total data volume is reported as approximately $N$4 PB, and public access is organized through the Jiutian collaboration website, with gradual release of high-level data and contact-based access for full or low-level data (Han et al., 27 Mar 2025).

A possible source of confusion is the term “JiuTian,” which also appears in unrelated work on the JiuTian Intelligent Network Simulation Platform for wireless communications (Zhao et al., 2023) and JiuTian Chuanliu, a large spatiotemporal urban-sensing model (Han et al., 26 Oct 2025). Those systems share the name but are distinct from Jiutian-300. In the cosmological literature, Jiutian-300 specifically denotes the $N$5 primary-run $N$6-body simulation within the Jiutian simulations for CSST extragalactic surveys (Han et al., 27 Mar 2025).

Taken together, the cited works portray Jiutian-300 as a high-resolution cosmological backbone rather than a single-purpose simulation. Its role is defined as much by the derivative pipelines built on top of it as by its raw particle realization: halo and subhalo catalogs, merger trees, semi-analytic galaxies, mock light cones, and post-processed reionization fields all depend on the same underlying density evolution (Han et al., 27 Mar 2025, Ma et al., 10 Mar 2026). This suggests that Jiutian-300 is best understood as infrastructure for a family of precision cosmology and galaxy-evolution workflows, with well-documented strengths in resolution and equally explicit caveats in volume-limited and inner-halo regimes (Xu, 11 Aug 2025).