Hong Guo

We used 50 Sobol-sampled VariableTNG (VTNG) simulations, varying eight subgrid parameters at a fixed cosmology and initial conditions, to determine which baryonic processes regulate galaxies and black holes at z = 6 and z = 8. We compared the simulations with recent high-redshift measurements of the stellar mass function (SMF), star-forming main sequence, stellar and gas-phase mass–metallicity relations, stellar mass–size relation, and black-hole host and accretion properties. The simulations reproduced several broad trends in these observables, although differences remain for the gas-phase metallicity, galaxy size, and the most extreme black-hole populations. Given the substantial uncertainties in both the physical modelling and the observational inference of high-redshift galaxy properties, we regard these differences as diagnostic tensions rather than definitive model failures. Random-forest analyses reveal a clear hierarchy in parameter sensitivity. The abundance of low-mass galaxies is primarily regulated by stellar feedback, particularly the supernova temperature T _SN and thermal wind fraction τ _w , whereas the sensitivity of the scatter in the star-forming main sequence is weaker and redshift dependent. The high-accretion tail of black-hole growth depends on black-hole seeding and feedback parameters, but also on T _SN , suggesting that stellar feedback indirectly regulates rapid black-hole growth through its impact on the available gas supply. For an independent VTNG-sized volume, the estimated field-to-field scatter in the integrated SMF abundance exceeds the parameter-driven scatter by factors of approximately 2.3 and 1.6 at z = 6 and z = 8, respectively. This volume-dependent scatter limits the detectability of the subgrid response in individual small fields, but it does not alter the intrinsic response isolated by the fixed-initial-condition experiment. Our controlled experiment identifies stellar feedback as a common physical link between early low-mass galaxy formation and rapid black-hole growth.

Context . Cosmic filaments represent the environments in which most galaxies form and evolve. However, the spatial distribution of filaments and the link between galaxy properties and their positions relative to filaments remains unclear, particularly at high redshifts. Aims . In this work, using the deep-field catalog COSMOS-Web Data Release 1, we construct a filament catalog spanning 0.5 < z < 3.5 that can be directly applied to studies of galaxy evolution and the galaxy–large-scale-structure connection at the peak epoch of galaxy and black hole formation. Methods . We developed a new procedure based on the DisPerSE method that fully incorporates the probability distribution functions (PDFs) of galaxy photometric redshifts by generating multiple realizations for each tomographic 2D slice. We then stacked these realizations to construct “filament probability maps” ( w _fil maps), from which filaments were subsequently extracted. The filament extraction parameters were optimized using mock catalogs generated from TNG simulations by minimizing the discrepancies between 3D and projected 2D filaments. Results . Applying this procedure to the COSMOS-Web data, we detected 12 523 filaments (comprising 136 210 segments) across 0.5 < z < 3.5 and released a filament catalog, a companion segment catalog, and filament probability maps for each slice. Validation against astrophysical properties shows a strong agreement between the extracted filaments and those in the simulations, supporting the robustness of the filament extraction. Conclusions . These data products provide a robust foundation for investigating galaxy–environment coevolution at cosmic noon and beyond.

We present an untargeted survey of 21 cm H i absorption systems based on the second data release of the FAST All Sky H I survey (FASHI DR2), covering approximately 19,500 deg ² at z ≲ 0.09. A total of 132 H i absorbers are identified, including approximately 60 new discoveries, forming one of the largest homogeneous samples of low-redshift H i absorbers assembled to date. The sample extends to continuum flux densities as low as 2.6 mJy, substantially below the limits of previous flux-limited surveys. The absorber population is dominated by narrow systems ( W ₅₀ < 100 km s ⁻¹ ), while broad absorbers ( W ₅₀ > 200 km s ⁻¹ ) account for 13.6% of the sample. Most absorbers are optically thin, with a median optical depth of τ _HI ≈ 0.14. The velocity-offset distribution is broadly symmetric about the systemic velocities of the host galaxies. The associated absorbers are preferentially found in massive, actively star-forming galaxies. We find tentative evidence for a weak anticorrelation between H i column density and stellar mass, although the relation exhibits substantial scatter. These results provide the first statistical characterization of the low-redshift H i absorber population based on the FASHI DR2 sample and establish a valuable benchmark for future H i absorption surveys with next-generation radio facilities.

Because groups are directly associated with halos, they allow for considerably simpler theoretical modeling than approaches based on individual galaxies. We therefore propose to use voids identified in galaxy group catalogs, referred to as group-voids, to investigate the cosmic large-scale structure (LSS). Using the reference mock galaxy redshift survey designed for the Chinese Space-station Survey Telescope, we build two galaxy group catalogs representing ideal and realistic scenarios, derived from galaxy samples with 100% and roughly 30% spectroscopic redshift completeness, respectively. We then identify voids in these two mock group catalogs, as well as in the underlying halo catalog, and measure two void statistics, the void size function and the void density profile, within five redshift intervals spanning z = 0–1.0. We compare the statistics obtained from two kinds of voids: those defined by galaxy groups (group-voids) and those defined by dark matter halos (halo-voids). In the void-finding process, we adopt the brightest central galaxy as the group center to improve the accuracy of the inferred void centers. Our analysis shows that void statistics derived from group-voids with spectroscopic redshift completeness of at least 40% can faithfully reproduce the corresponding statistics from halo-voids. Even when the redshift completeness of galaxies falls to as low as 30%, we can still reliably describe group-voids via halo-voids by incorporating a redshift error term. This indicates that group-voids are a promising tool for probing LSS and offer a valuable complement to standard void studies, which is especially advantageous for emulator-based methods.

The Hundred-deg ² H I Deep (HD ² ) survey carried out with the Five-hundred-meter Aperture Spherical Telescope is planned to map a contiguous region within the DESI DR1 footprint, achieving an effective integration time of 20 minutes for each pointing and a uniform detection sensitivity of 0.28 mJy beam ⁻¹ at 4.8 km s ⁻¹ resolution. We present early results from the pilot HD ² survey: a 10 deg ² field overlapping with the Hyper Suprime-Cam Subaru Strategic Program and the DESI early data release SV3, observed with an integration time of 7.3 minutes beam ⁻¹ and an rms of 0.45 mJy beam ⁻¹ at 4.8 km s ⁻¹ resolution. We identify 339 H I sources at z < 0.09, corresponding to ∼34 detections per deg ² , nearly 6 times higher than the detection rate of the wide-field surveys. Optical counterparts are primarily identified using DESI redshifts, yielding a matching rate and correctness exceeding 90% for galaxies with r < 19.5 mag, a substantial improvement over the Sloan Digital Sky Survey. Under the constraint of r < 17.8 mag and 0.01 < z < 0.05, nearly 50% of galaxies in the DESI Bright Galaxy Survey samples have H I detections in this pilot survey. The optical properties of these H I -detected galaxies span nearly the entire parameter range of the DESI sample. The gas fraction scaling relations versus stellar mass, stellar mass surface density, near-UV (NUV) − r , and specific star formation rate are consistent with previous surveys, e.g., ALFALFA, DINGO, and xGASS. These results justify the feasibility of the full HD ² survey, which will build a high-completeness H I census over a contiguous area to probe the cold gas scaling relations of galaxies over different scales.

The slitless spectroscopic method employed by missions such as Euclid and the Chinese Space-station Survey Telescope (CSST) faces a fundamental challenge: spectroscopic redshifts derived from their data are susceptible to emission-line misidentification due to the limited spectral resolution and signal-to-noise ratio. This effect systematically introduces interloper galaxies into the sample. Conventional strict selection not only struggles to secure high redshift purity but also drastically reduces completeness by discarding valuable data. To overcome this limitation, we develop an XGBoost classifier that leverages photometric properties and spectroscopic diagnostics to construct a high-purity redshift catalog while maximizing completeness. We validate this method on a simulated sample with spectra generated by the CSST emulator for slitless spectroscopy. Of the ∼62 million galaxies that obtain valid redshifts (parent sample), approximately 43% achieve accurate measurements, defined as ∣Δ z ∣ ≤ 0.002(1 + z ). From this parent sample, the XGBoost classifier selects galaxies with a selection efficiency of 42.3% on the test set and 42.2% when deployed on the entire parent sample. Crucially, among the retained galaxies, 96.6% (parent sample: 96.5%) achieve accurate measurements, while the outlier fraction (∣Δ z ∣ > 0.01(1 + z )) is constrained to 0.13% (0.11%). We verified that simplified configurations that exclude either spectroscopic diagnostics (except the measured redshift) or photometric data yield significantly higher outlier fractions, increasing by factors of approximately 3.5 and 6.3, respectively, with the latter case also introducing notable catastrophic interloper contamination. This framework effectively resolves the purity-completeness trade-off, enabling robust large-scale cosmological studies with CSST and similar surveys.

The China Space Station Telescope (CSST) will simultaneously conduct wide-field multiband photometric imaging and spectroscopic slitless surveys, poised to significantly advance cosmology and galaxy evolution research. Meeting CSST’s cosmological goals requires precise redshifts ( σ _NMAD ≲ 0.002–0.005) from its low-resolution ( R ∼ 200) and potentially blended slitless spectra. We present BayeSED3, extended for Bayesian full spectrum analysis, incorporating detailed nebular emission modeling (via CLOUDY) and a robust Bayesian treatment of the model scaling factor, enhancing reliability over optimization techniques for low signal-to-noise ratio (SNR) spectra. Validated on realistic mock data generated with the CSST Emulator for Slitless Spectroscopy (CESS; median SNR of 1.65, instrumental and self-blending effects included), our method achieves excellent redshift precision with three-band (GU+GV+GI) spectroscopy, exceeding requirements: σ _NMAD = 0.0008 (∼80% success rate) for star-forming galaxies and σ _NMAD = 0.0015 (∼50% success rate) for quiescent galaxies. Stellar mass ( M _* ; σ _NMAD ≈ 0.015 dex for star-forming galaxies, ≈0.016 dex for quiescent galaxies) and star formation rate ( σ _NMAD ≈ 0.05 dex for star-forming galaxies, especially at SNR > 1) can also be reliably recovered. While spectral self-blending increases scatter ( σ _NMAD ) by ≳30%, combining spectroscopy with CSST’s seven-band photometry crucially improves accuracy, especially for quiescent galaxies and in data-limited scenarios. Combining photometry with single-band spectroscopy leads to reasonable redshift estimation. While GU+photometry shows limited performance, GI+photometry yields success rates of >60% (for star-forming galaxies) and >40% (for quiescent galaxies) with σ _NMAD ≲ 0.002, and GV+photometry achieves success rates of >35% (for star-forming galaxies) and ∼40% (for quiescent galaxies) at similar precision. Our comprehensive Bayesian framework thus provides a robust tool for precise galaxy characterization, enhancing scientific returns from CSST’s unique dataset despite inherent slitless spectroscopy challenges.