Shuai Feng

Blue horizontal-branch (BHB) stars are ideal tracers for mapping the structure of the Galactic stellar halo. However, traditional spectroscopic identification is limited by data quality and sample size, while broadband photometric methods often achieve only moderate completeness and purity. Building upon the color-space BHB identification method of G. Hu et al., we synthesize SkyMapper ( u , v , g , z ) photometry from DESI MWS DR1 spectroscopy and identify 9237 BHB candidates in the ( g − z ) ₀ –( u − v ) ₀ color space using the HDBSCAN clustering algorithm. We then construct a kernel density estimation (KDE) Bayesian probability model with capture–recapture (C–R) prior to assign posterior membership probabilities, achieving a probability-weighted purity of 88.9% and completeness of 94.2%. Applying an escape-velocity cut based on the Galactic gravitational potential, we remove 1461 contaminants with unphysical kinematic parameters, yielding a clean photometric BHB sample S c of 7776 stars (retention rate R _keep = 84.2%). Systematic analysis of the contaminants reveals that they are predominantly faint sources ( g ∼ 20 mag) with very low signal-to-noise ratios (SNRs; median SNR < 5). When the BHB color–luminosity relation is incorrectly applied to these objects, their space velocities are amplified beyond the Galactic escape limit, confirming that the escape-velocity filter essentially acts as a physical detector of low-SNR-driven distance inflation.

Galaxy quenching, the cessation of star formation, can proceed in spatially distinct ways, commonly described as inside-out or outside-in. However, the inferred quenching pattern depends strongly on how quenched or quenching regions are defined observationally. We utilize a sample of ∼10,000 galaxies from the Mapping Nearby Galaxies at Apache Point Observatory DR17 survey to systematically compare four widely used diagnostics of star formation suppression—the specific star formation rate (sSFR), the 4000 Å break ( D _n 4000), poststarburst (PSB), and low-ionization nuclear emission-line region (LI(N)ER) emission—to examine how tracer choice influences the inferred spatial quenching pattern. Using the nonparametric method developed by L. Lin et al., we classify galaxies into inside-out and outside-in quenching modes based on the location on the plane of the fraction of the quenched area ( F _q ) and the concentration of the quenched area ( C _q ). We find that sSFR criterion yields comparable proportions of galaxies classified as inside-out and outside-in, while the D _n 4000 and LI(N)ER diagnostics strongly favor inside-out patterns. Because PSB traces a distinct transitional phase, PSB-selected spaxels occupy a different region of the F _q – C _q plane. Across most diagnostics, the fraction of galaxies classified as inside-out increases with stellar mass, while outside-in patterns are more common in lower-mass systems, especially among satellites. In contrast, the dependence of quenching mode on halo mass is weaker and less consistent across diagnostics. These differences show that the tracers probe complementary stages and timescales of star formation suppression, and together provide a more complete view of spatially resolved quenching.

The magnitude gap between the central and satellite galaxies encodes information about the mass accretion history of a dark matter halo and serves as a useful observational probe for the mass distribution in a halo. In this work, we perform the first weak lensing test of the connections between the magnitude gap and the halo profile. We measure the halo profiles of isolated central galaxies (ICGs) selected primarily from the Sloan Digital Sky Survey Main Galaxy Sample. Halo mass and concentration are inferred by fitting stacked lensing profiles in bins of central luminosity, L _c , and the central-satellite magnitude gap, L _gap . We detect dependence on the magnitude gap in both halo properties. The dependence is the strongest in the ICG luminosity range of 10 ^10.3 < L _c [ h ⁻² L _⊙ ] ≤ 10 ^10.7 , where halos with smaller gaps have higher masses and lower concentrations. When 10 ^10.7 < L _c [ h ⁻² L _⊙ ] ≤ 10 ^11.1 , however, no significant gap dependence is detected. In the range of 10 ^9.9 < L _c [ h ⁻² L _⊙ ] ≤ 10 ^10.3 , a disordering of the gap dependence is marginally observable. We compare the observational results with predictions by two light-cone catalogs built from the Illustris TNG300 and the Millennium simulations. The gap dependence in the two mock samples show overall consistency with observations, but neither matches them in all L _c bins to a quantitative level, and the flip in the gap dependence in the lowest luminosity bin is not reproduced in the mocks. We also compare the significance of the gap dependence on halo mass and concentration and find that our measurement prefers the halo-mass dependence over the concentration.

We investigate the bar fraction in galaxy pairs from the SDSS to assess how galaxy interactions affect bar structures. Compared to isolated galaxies, close pairs exhibit a significantly reduced bar fraction at projected separations within 25 kpc. This reduction is driven almost entirely by systems showing clear merger or disturbance signatures, indicating that tidal interactions suppress bars. The decline is dominated by a decrease in weak bars, while the fraction of strong bars remains largely unchanged. Bar suppression is primarily associated with major mergers and is strongest in massive host galaxies. A weaker but statistically significant suppression is detected in minor mergers only for massive galaxies with small bulges. In contrast, no significant dependence of bar suppression on the relative orientation between pair members is found. These findings provide observational evidence that tidal perturbations in major mergers play a key role in regulating bar evolution.

We developed a Python package GEHONG to mock the three-dimensional spectral datacube under the observation of an ideal telescope for the Integral Field Spectrograph of the Chinese Space Station Survey Telescope. This package can generate one-dimensional spectra corresponding to local physical properties at specific positions according to a series of two-dimensional distributions of physical parameters of target sources. In this way, it can produce a spatially resolved spectral cube of the target source. Two-dimensional distributions of physical parameters, including surface brightness, stellar population, and line-of-sight velocity, can be modeled using the parametric model or based on real observational data and numerical simulation data. For the generation of one-dimensional spectra, we have considered four types of spectra, including the stellar continuum spectra, ionized gas emission lines, Active Galactic Nucleus (AGN) spectra, and stellar spectra. That makes GEHONG able to mock various types of targets, including galaxies, AGNs, star clusters, and H II regions.

The Multi-Channel Imager (MCI), one of the instruments aboard the Chinese Space Station Survey Telescope, is designed to simultaneously observe the sky in three filters, covering wavelengths from near-ultraviolet to near-infrared. With its large field of view ( 7 . ′ ⁡ 5 × 7 . ′ ⁡ 5 ), MCI is particularly well-suited for observing galaxy clusters, providing a powerful tool for investigating galaxy evolution, dark matter and dark energy through gravitational lensing. Here we present a comprehensive simulation framework of a strong lensing cluster as observed by MCI, aiming to fully exploit its capabilities in capturing lensing features. The framework simulates a strong lensing cluster from the CosmoDC2 catalog, calculating the gravitational potential and performing ray-tracing to derive the true positions, shapes and light distribution of galaxies within the cluster field. Additionally, the simulation incorporates intra-cluster light (ICL) and spectral energy distributions (SEDs), enabling further strong lensing analyses, such as ICL separation from galaxy light and mass reconstruction combining strong and weak lensing measurements. This framework provides a critical benchmark for testing the MCI data pipeline and maximizing its potential in galaxy cluster research.

The Chinese Space Station Survey Telescope (CSST), a two-meter aperture astronomical space telescope under China’s manned space program, is equipped with multiple back-end scientific instruments. As an astronomical precision measurement module of the CSST, the Multi-Channel Imager (MCI) can cover a wide wavelength range from ultraviolet to near-infrared with three-color simultaneous high-precision photometry and imaging, which meets the scientific requirements for various fields. The diverse scientific objectives of MCI require not only a robust spaceborne platform, advanced optical systems, and observing facilities but also comprehensive software support for scientific operations and research. To this end, it is essential to develop realistic observational simulation software to thoroughly evaluate the MCI data stream and provide calibration tools for future scientific investigations. The MCI instrument simulation software will serve as a foundation for the development of the MCI data processing pipeline and will facilitate improvements in both hardware and software, as well as in the observational operation strategy, in alignment with the mission’s scientific goals. In conclusion, we present a comprehensive overview of the MCI instrument simulation and some corresponding performances of the MCI data processing pipeline.

The Chinese Space Station Survey Telescope (CSST) is a next-generation Stage-IV facility renowned for its wide field of view, high image quality, and multi-band observational capabilities. Among the five instruments onboard the CSST, the Integral Field Spectrograph (IFS) offers the unique ability to simultaneously capture spatial and spectral information across a field of view of no less than 6″ × 6″. Key advantages of the IFS include a high spatial resolution of 0 . ″ 2 and a broad spectral coverage from 350 to 1000 nm, making it an ideal instrument for studying physical processes in the vicinity of supermassive black holes within galaxies. To more accurately assess the technical and scientific performance of the CSST-IFS, it is essential to develop a simulation tool that incorporates realistic effects from all optical components. Such a simulation will form an integral part of the CSST-IFS data and pipeline system, enabling the development of the data reduction pipeline well ahead of actual observations. This paper presents an end-to-end simulation workflow for the CSST-IFS, incorporating a wide range of instrumental effects that may influence its spectral and imaging performance. The simulation accounts for optical diffraction effects introduced by all components, such as image slicers and slit array, as well as sub-pixel effects from gratings. It also includes various detector noises, frame-shifting effects, and charge-transfer inefficiency. Real observational conditions-such as target Doppler shift, cosmic rays, and other in-orbit operational effects-are also considered. We describe the technical implementation of the simulation and present results that quantitatively characterize key instrument parameters.

This study probes the inside-out and outside-in quenching status of galaxies to understand the internal and external quenching sources responsible and their roles in galaxy evolution. We utilize data from the MaNGA survey and MaNGIA, a mock MaNGA sample derived from the high-resolution TNG50 simulation, comparing their spatially resolved galaxy properties to address this knowledge gap. Our analysis begins with an assessment of the integrated and spatially resolved star-forming main sequence, finding good agreement between the two datasets. We also observe excellent consistency in radial profiles of stellar mass surface density. Using the surface density of the specific star formation rate (Σ _sSFR ) to identify quenched regions, we investigate inside-out and outside-in quenching modes across different stellar masses and environments via three classification methods. We find broad consistency between MaNGA and MaNGIA for high-mass galaxies, where inside-out quenching dominates regardless of environment. However, for lower-mass galaxies, we find discrepancies in the dominant quenching mode in middle halo mass environments. The environmental dependence of inside-out quenching in both MaNGA and MaNGIA aligns with an internal quenching scenario, such as feedback from active galactic nuclei or morphology quenching. In contrast, MaNGA reveals a weaker environmental dependence for outside-in quenching, suggesting a roughly even contribution of multiple physical processes, whereas MaNGIA indicates a stronger environmental role, with group environments likely playing a significant part.

We introduce a non-parametric approach, the Stellar Population Synthesis with Equivalent Widths (SEW) method, to reconstruct spectrally-resolved attenuation curves for 169 568 star-forming galaxies from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7). Composite attenuation curves, stacked by stellar mass and inclination, reveal systematic trends: a higher stellar mass correlates with steeper slopes (lower $R_V$), while edge-on galaxies exhibit flatter curves due to geometric saturation effects. This flattening occurs because, as optical depth increases along the line of sight, the observed light becomes increasingly dominated by emission from the outer, less obscured layers of the galaxy. Using a simplified radiative transfer treatment based on a uniform dust-star mixture, we find the inclination-dependent slope variations are consistent with geometric effects, whereas the mass-dependent slope steepening indicates evolution in intrinsic dust properties, suggesting feedback-driven grain fragmentation in massive galaxies. Additionally, intermediate-scale structures are tentatively identified in the attenuation curves at approximately 4870, 6370, and 7690 Å. These results illustrate how the interplay among dust-star geometry, grain size evolution, and the galactic environment shapes attenuation curves.