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Shiyin Shen

Publications and source records attributed to Shiyin Shen.

At least 19 recordsLinked to original sources
arXiv2026

Widespread Inflows Reveal Baryonic Cycling in Star-forming and Quiescent Galaxies

Cool-gas inflows, required to sustain star formation, have been fundamental in simulations yet remained observationally elusive. Using DESI spectroscopy of ~30,000 galaxies, we identify coherent inflowing gas (~100 km/s) in 20-50% of the sample, yielding a population-level census of gas flows. We uncover a striking inversion: inflows are detected in quiescent galaxies, whereas star-forming systems are dominated by gravitationally bound outflows. At fixed age, galaxies with inflows, outflows, or no/weak flows share similar masses, environments, and structures, indicating that these properties do not differentiate flow states. Instead, gas-flow state is linked to stellar population age and recent evolutionary history, consistent with age-dependent gas flows in two regimes. In some star-forming galaxies, elevated star formation surface densities drive outflows that recycle on ~0.5 Gyr timescales, consistent with a galactic fountain. In quiescent systems, low-level ``drizzling'' inflows persist, consistent with slowly cooling enriched halo gas and weak radio-mode nuclear activity. Broad gas-phase metallicity distributions---and absence of a pristine dilution signature---indicate that detected inflows are predominantly recycled or enriched. Detectability is modulated by dust, ionization, and geometry: in star-forming disks, inflowing gas lies near the disk plane and is obscured or ionized, while outflow hosts exhibit higher dust and metal content. As star formation declines, cold-outflow signatures weaken, and recycled or slowly cooling gas is more readily detected as inflow. Post-starburst galaxies provide snapshots of this transition. Our results resolve the scarcity of observed inflows, provide evidence for widespread gas accretion and recycling in present day galaxies, and establish an observational framework linking gas flows to star formation, chemical evolution, and galaxy structure.

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arXiv2026

Star Formation Evolution in Galaxy Pairs: Constraints from Morphological Disturbances and Recent Star Formation Histories

Galaxy interactions can enhance star formation, but how star formation evolves during galaxy interactions remains poorly constrained by observations. We combine pair separation, morphological disturbance, and recent star formation history to study this evolution. We measure morphological disturbance with the shape asymmetry parameter ($A_{\rm shape}$) using deep images from the DESI Legacy Surveys, and use Galaxy Zoo DESI classifications as an independent test. We infer recent star formation histories by comparing SFR and $\mathrm{EW}(\mathrm{H}α)$, which trace current star formation, with $\mathrm{EW}(\mathrm{H}δ_A)$ and $D_n4000$, which are sensitive to stellar populations formed over longer timescales. At small projected separations, strongly disturbed galaxies show the strongest enhancements in SFR and $\mathrm{EW}(\mathrm{H}α)$, indicating that close encounters trigger strong star formation. At intermediate separations ($d_{\rm p}\sim100\,\mathrm{kpc}$), their current star formation is only moderately enhanced, but their $\mathrm{EW}(\mathrm{H}δ_A)$ enhancement is the strongest. This indicates a larger contribution from intermediate-age stars formed during stronger star formation in the past $\sim0.1$--$1\,\mathrm{Gyr}$. The TNG100 analysis shows that this pattern results from rapid changes in SFR around close passage. SFR rises sharply during the encounter and declines as the galaxies move apart, while tidal disturbances remain visible. As short-lived massive stars disappear and intermediate-age A-type stars begin to dominate the spectrum, the $\mathrm{EW}(\mathrm{H}δ_A)$ enhancement peaks later than the SFR enhancement. Our results provide important observational evidence for the evolution of SFR along the merger sequence.

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arXiv2026

From DESI to Euclid: A Generative Bridge to Improve Measurements of Galaxy Structure

Ground-based seeing imprints size-dependent biases on galaxy structural parameters, yet the high-resolution space-based imaging needed to improve these measurements currently covers only a small fraction of the sky. We close this gap with a generative model that produces Euclid-like VIS predictions from DESI imaging of Bright Galaxy Survey (BGS) targets. Our predictions remain Fourier-correlated with Euclid VIS images down to 0.37'', compared with 1.41'' and 1.00'' for the DESI $r$- and $z$-band inputs, corresponding to improvements by factors of ${\sim}3.8$ and ${\sim}2.7$, respectively. Although this correlation does not extend down to 0.16'', the characteristic Euclid VIS PSF FWHM, structural measurements from these predictions already show reduced biases relative to the DESI $r$-band structure measurements: the Petrosian radius bias falls to +0.072'' (from -0.845''), independent of galaxy size; the bias in the Sérsic effective radius ($R_{\rm e}$) drops to -0.018'' (from -0.322''); and the Sérsic-index bias to +0.093 (from +0.262). We release these predictions over the Euclid DR1 footprint as the Euclid-like Predictions of BGS (\textbf{E-BGS}), which can be blindly validated once DR1 is public.

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arXiv2026

Towards optimal photometric calibration of digital astronomical plates with deep learning

Photometric calibration of digitized photographic plates is commonly modeled with separable magnitude-, color-, and position-dependent terms, but this separability can break down when image quality varies across the field in a magnitude-dependent way, leaving coupled spatial systematics in the residuals. We introduce a deep-learning calibration framework, the Multi-Feature Fused Network (MFF-Net), which takes instrumental magnitude, color, and pixel coordinates as input and learns a single nonlinear correction that jointly captures their coupled dependencies. Tests on 1{,}200 digitized Chinese plates show that MFF-Net consistently outperforms the MYX25 method (Ma et al. 2025), improving the 5th--95th percentile precision from 0.11--0.26~mag to 0.08--0.18~mag and delivering an approximately factor-of-two gain for bright sources. The learned correction largely removes the magnitude--position coupling seen in post-calibration residual maps, enabling higher-precision plate photometry and more reliable use of large historical plate archives.

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arXiv2026

Radial Distributions of Star Formation and Gas-phase Metallicity in Spiral-Elliptical Galaxy Pairs

Using integral field spectroscopy from SDSS-IV MaNGA, we investigate the radial distributions of star formation rate (SFR) and gas-phase metallicity in spiral galaxies that reside in spiral-elliptical (S+E) pairs. Spirals in S+E pairs show suppressed central star formation and elevated metallicities, whereas spirals in spiral-spiral pairs exhibit centrally enhanced star formation and reduced metallicities. The degree of SFR suppression and metallicity enhancement in S+E pairs depends on the masses of the pair members. Spirals with more massive elliptical companions experience stronger star-formation suppression and larger increases in metallicity, while lower-mass spirals show more pronounced metallicity enhancement. In addition, within S+E systems, galaxies with asymmetric gas velocity fields display enhanced SFR and higher metallicities, whereas those with symmetric velocity fields exhibit clear central suppression. Based on these results, we infer that in S+E pairs, the spiral galaxy experiences suppressed gas accretion once it enters the hot circumgalactic medium of its early-type companion, which leads to the observed decline in star-formation activity. When a close encounter takes place, tidal perturbations can compress the remaining cold gas and trigger enhanced star formation, producing rapid chemical enrichment and the associated increase in metallicity.

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arXiv2026

Inside-Out vs. Outside-In Quenching of MaNGA Galaxies: Dependence on Stellar Mass and Environment

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 approximately 10,000 galaxies from the Mapping Nearby Galaxies at APO (MaNGA) DR17 survey to systematically compare four widely used diagnostics of star formation suppression: specific star formation rate (sSFR), the 4000 Å break (Dn4000), post-starburst (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 non-parametric method developed by Lin et al. (2019), 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 (Fq) and the concentration of quenched area (Cq). We find that the sSFR criterion yields comparable proportions of galaxies classified as inside-out and outside-in, while Dn4000 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 Fq-Cq 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.

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arXiv2026

Enhancing astrometric registration of Chinese historical Astronomical Digital Plates with deep learning

China has systematically collected nighttime astronomical plates since 1900, creating a large historical dataset that has been digitized with optical scanners. For astrometric registration of these digitized plates, sources were first extracted using SExtractor, and then matched astrometrically with Astrometry.net and the Gaia catalog. However, suboptimal early storage conditions and subsequent environmental deterioration have impeded accurate source matching, resulting in processing failures for several thousand digitized plates. In this work, we introduce a Transformer-based classification model that takes cutouts of SExtractor-detected sources as input and leverages multi-scale feature fusion to identify trustworthy stellar sources on the plates. Trained on plates with successful astrometric calibration, our AI-based classifier was then applied to SExtractor detected sources of 1883 digitized plates, enabling us to complete the astrometric registration for 1353 of them. This AI-augmented pipeline streamlines the processing of historical plate archives and enhances their scientific value for long-term time-domain astronomical studies.

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arXiv2026

Beyond Mass and Multiscale Environments: What Shapes Low Surface Brightness Galaxies? Evidence from MaNGA

The origin of low surface brightness (LSB) galaxies remains a key open question in galaxy formation, reflecting the balance internal mechanisms and environmental influence. Using MaNGA integral-field spectroscopy, we investigate whether LSB and high surface brightness (HSB) galaxies of comparable stellar mass ($9 < \log M_\ast < 10$) occupy distinct environments or differ primarily through internal evolution. Our late-type sample comprises 113 central and 29 satellite LSB galaxies, and 374 central and 142 satellite HSB galaxies. We characterize environments on scales from 100 kpc to 10 Mpc, analyzing radial profiles of stellar mass surface density ($Σ_\ast$), star formation activity, and gas-phase metallicity. Central LSB and HSB galaxies inhabit similarly low-density large-scale ($>$200 kpc) environments, but LSB galaxies are more isolated on small scales ($\sim$100 kpc). Even after matching in stellar mass and environment, LSB galaxies show systematically lower $Σ_\ast$, $Σ_{SFR}$, and metallicities, often hosting diffuse, weakly star-forming bulges embedded in extended disks. These results indicate that LSB structure and star formation are not primarily governed by large-scale environment or halo mass. While secondary halo properties such as spin, concentration, or gas accretion history are often invoked, their environmental dependence appears weak. Instead, LSB-HSB differences for centrals likely reflect divergent assembly or interaction histories and internal processes -- such as angular momentum-driven disk evolution or inefficient gas conversion -- largely decoupled from large-scale environment. Nonetheless, environment still influences the observed star formation and chemical differences between central and satellite LSB galaxies.

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arXiv2026

The Universe Favors Primes: A Study in the Primality of Cosmic Structures

The cosmological principle states that the universe is uniform and does not favor any specific position or direction. However, research conducted by \cite{Shen2025} has revealed that the universe demonstrates a notable inclination towards parity-odd states. Furthermore, it remains uncertain whether the universe also favors prime numbers. In this study, we examine the largest available catalogs of galaxy groups to investigate this hypothesis. Specifically, we assess whether the number of galaxies within a galaxy group or cluster is more likely to be a prime number. Our results strongly suggest that the universe does indeed have a preference for prime numbers, with findings exceeding the 4.1 sigma significance threshold. This insight explains why the Primes consistently triumphs over Unicorn. Consequently, it may be necessary to consider revising the cosmological principle in the context of a higher-dimensional feature space. Moreover, our research establishes a connection between the Riemann Zeta function and cosmology pioneeringly, paving the way for the development of Cosmozetaology.

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arXiv2026

SDSS-IV MaNGA: Distinct Structural Growth and Star Formation in Low and High Surface Brightness Disks

We analyze a clean sample of 1,118 late-type, face-on galaxies without AGN contamination from the MaNGA survey. Their photometric structures are quantified via two-component (bulge+disk) decompositions on deep $g$-band images from the DESI Legacy Survey. Using a disk central surface brightness of $μ_{\rm 0,d,cor}$(g) = 22 $\pm$ 0.3 mag arcsec$^{-2}$ (corrected for inclination and cosmic dimming) as the classification threshold, we identify 159 low surface brightness (LSB) galaxies, 388 LSB candidates, and 571 high surface brightness (HSB) galaxies. LSB galaxies are predominantly low-mass ($M_\ast < 3 \times 10^{10}$ M$_\odot$), exhibiting 29\% larger effective radii, 15\% lower star formation rates (SFRs), and 12\% reduced gas-phase metallicities than HSB counterparts at comparable masses. These differences cause systematic offsets from standard scaling relations. Despite comparable gas content, LSB galaxies host older stellar populations, longer gas depletion times, and less efficient star formation. Spatially resolved analyses further reveal that LSB galaxies display centrally suppressed $Σ_{\rm SFR}$, flatter SFR gradients, and rising specific SFR profiles toward their outskirts. Together with steeper negative metallicity gradients, these trends suggest ongoing gas accretion fueling outer-disk star formation. Consistently, the outer regions of LSB galaxies exhibit stronger H$δ_A$ absorption and lower D$_n$4000 indices, indicating fading A-star populations. Moreover, LSB galaxies show lower $Σ_{\ast}$ across all $R/R_e$ and more centrally depleted stellar mass profiles on an absolute radial scale, compared with HSB and large-size star-forming galaxies. Collectively, LSB galaxies represent a distinct population with slow evolution, inefficient star formation, and continued susceptibility to late-time gas accretion and peripheral star formation.

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arXiv2026

Mock Observations for the CSST Mission: Integral Field Spectrograph--GEHONG: A Package for Generating Ideal Datacubes

We developed a Python package GEHONG to mock the three-dimensional spectral data cube under the observation of an ideal telescope for the Integral Field Spectrograph of the Chinese Space Station Telescope (CSST-IFS). 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, AGN spectra, and stellar spectra. That makes GEHONG able to mock various types of targets, including galaxies, AGNs, star clusters, and HII regions.

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arXiv2026

Reduction of bar fraction in paired galaxies in the SDSS

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.

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arXiv2026

Galaxy Light profile neural Networks (GaLNets). II. Bulge-Disc decomposition in optical space-based observations

Bulge-disk (B-D) decomposition is an effective diagnostic to characterize the galaxy morphology and understand its evolution across time. So far, high-quality data have allowed detailed B-D decomposition to redshift below 0.5, with limited excursions over small volumes at higher redshifts. Next-generation large sky space surveys in optical, e.g. from the China Space Station Telescope (CSST), and near-infrared, e.g. from the space EUCLID mission, will produce a gigantic leap in these studies as they will provide deep, high-quality photometric images over more than 15000 deg2 of the sky, including billions of galaxies. Here, we extend the use of the Galaxy Light profile neural Network (GaLNet) to predict 2-Sérsic model parameters, specifically from CSST data. We simulate point-spread function (PSF) convolved galaxies, with realistic B-D parameter distributions, on CSST mock observations to train the new GaLNet and predict the structural parameters (e.g. magnitude, effective radius, Sersic index, axis ratio, etc.) of both bulge and disk components. We find that the GaLNet can achieve very good accuracy for most of the B-D parameters down to an $r$-band magnitude of 23.5 and redshift $\sim$1. The best accuracy is obtained for magnitudes, implying accurate bulge-to-total (B/T) estimates. To further forecast the CSST performances, we also discuss the results of the 1-Sérsic GaLNet and show that CSST half-depth data will allow us to derive accurate 1-component models up to $r\sim$24 and redshift z$\sim$1.7.

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arXiv2026

ELFO: A Python Package for Emission Line Fitting Optimization in Integral Field Spectroscopy Data

Integral field spectroscopy (IFS) provides spatially resolved spectra, enabling detailed studies that address the physical and kinematic properties of the interstellar medium. A critical step in analyzing IFS data is the decomposition of emission lines, where different velocity components are often modeled with Gaussian profiles. However, conventional fitting methods that treat each spectrum independently often yield spatial discontinuities in the fitting results. Here, we present Emission Line Fitting Optimization (ELFO), a Python package for IFS spectral fitting. ELFO uses the results of neighboring spectra to determine multiple initial guesses and selects the result that exhibits spatial smoothness. We tested ELFO on IFS data of two quasars obtained from the Multi-Unit Spectroscopic Explorer, where it successfully corrected anomalous fits, revealed previously unresolved substructures, and made large-scale kinematic structures more evident. With minor modifications, this method can also be easily adapted to other IFS data and different emission lines.

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arXiv2026

Non-Parametric Attenuation Curves in Local Star-Forming Galaxies: Geometry Effect, Dust Evolution, and ISS

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 (ISSs) 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.

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arXiv2025

Antarctic TianMu Staring Observation Project I: Overview and Implementation of the Prototype Telescope

Wide-field rapid sky surveys serve as critical observational methods for time-domain astronomical research. The Antarctic region, with several months of continuous dark nights annually, is an ideal site for time-domain astronomical observations. The Antarctic TianMu Staring Observation Project aims to deploy a fleet of small telescopes, adopting an array observation model to conduct time-domain optical observations in Antarctica, featuring wide-sky coverage, high-cadence sampling, long-period staring, and simultaneous multi-band measurements. Considering the severe challenges optical telescopes face in Antarctica, including extremely low temperatures, unattended operation, and limited power supply and network transmission, we have designed and developed the Antarctic TianMu prototype telescope based on drift-scan charge-coupled device technology. In October 2022, our prototype (with an aperture of 18 cm), named AT-Proto was transported to Zhongshan Station in Antarctica aboard China's 39th Antarctic Research Expedition. It has since operated stably and reliably in the frigid environment for over two years, demonstrating the significant advantages of this technology in polar astronomical observations. The experimental observation results of AT-Proto provide a solid foundation for the subsequent construction of a time-domain astronomy observation array in Antarctica.

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arXiv2025

Antarctic TianMu Staring Observation Project II: Data reduction and preliminary results

The Antarctic TianMu Staring Observation Program is a time-domain optical sky survey project carried out in Antarctica, capable of large sky coverage, high-cadence sampling, and long-period staring. It utilizes the exceptional observing conditions in Antarctica to conduct high-cadence time-domain sky surveys. At present, we have successfully developed an 18-cm aperture Antarctic TianMu prototype, which has been deployed at Zhongshan Station in Antarctica for two consecutive years of trouble-free observations, during which more than 300,000 original images were obtained. This paper systematically outlines the commissioning data of the prototype telescope in 2023, the primary data processing pipeline, and the preliminary data products. The core pipeline encompasses four key stages: Data preprocessing, instrumental effect correction, astrometric solution, and full-field stellar photometry. Here, we release the 2023 data products, which specifically include reduced image data and a photometric catalog, for which, preliminary analyses demonstrate robust performance. Using Gaia Data Release 3 as a reference catalog, the astrometric precision, quantified by the root mean square of positional errors, is determined to be better than approximately 2 arcseconds, validating the observational capabilities of the system. For a 30-second exposure, the detection limit in the G-band is achieved at 15.00~mag, with a detection threshold of 1.5~$σ$. The photometric errors are below 0.1~mag for the majority of stars brighter than 14.00~mag. Furthermore, it improves significantly, reaching better than 0.01~mag for most stars brighter than 11.00~mag and 12.00~mag when employing the adaptive aperture photometry and point spread function photometry methods, respectively.

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arXiv2025

The Velocity Map Asymmetry of Ionized Gas in MaNGA II. Correlation between Velocity Map Morphology, Star Formation, and Metallicity in Regular Disk Galaxies

The morphology of ionized gas velocity maps provides a direct probe of the internal gas kinematics of galaxies. Using integral field spectroscopy from SDSS-IV MaNGA, we analyze a sample of 528 low-inclination, regular disk galaxies to investigate the correlations between velocity map morphology, star formation rate, and gas-phase metallicity. We quantify velocity map morphology using harmonic expansion and adopt two complementary diagnostics: the global kinematic asymmetry, which traces non-axisymmetric perturbations, and the first-order term ratio, which captures axisymmetric radial motions. We find that galaxies with higher kinematic asymmetry are more likely to deviate from the scaling relations, typically lying either above or below the star formation main sequence and systematically below the mass-metallicity relation. In contrast, the first-order term ratio shows only a correlation with gas-phase metallicity in the low-mass range and no significant dependence on star formation rate. Moreover, galaxies below the mass-metallicity relation generally exhibit higher HI gas fractions. These results suggest that external gas accretion is the primary driver of the observed phenomena: inflowing metal-poor gas increases velocity map asymmetry in disk galaxies, dilutes the metallicity, and triggers enhanced star formation. Feedback-driven outflows, bar- and spiral-driven inflows, and galaxy mergers may also contribute, but likely play a secondary role.

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