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Zheng Zheng

Publications and source records attributed to Zheng Zheng.

At least 19 recordsLinked to original sources
arXiv2026

Lower central dark matter densities in nearby galaxies than predicted by simulations

Baryonic feedback in hydrodynamical simulations is typically invoked to alleviate the core--cusp problem in dwarf galaxies. Yet baryonic processes also induce adiabatic contraction of dark matter, producing overly steep density profiles and excessively high dark matter fractions in the inner regions of massive galaxies. The dark matter distribution of galaxies across a wide stellar-mass range is therefore a critical test for such simulations, but a comprehensive benchmark has remained absent. Here, we consistently measure the dark matter distribution from galaxy centres out to radii of 20--50 kpc for 136 nearby galaxies that together span the local mass--size relation over the stellar mass interval $10^9$--$10^{11.5}\,M_{\odot}$. We identify central regions with lower dark matter densities relative to $Λ$CDM simulation expectations---whose extent grows from about 10 kpc to $>50$ kpc as stellar mass increases from $10^{10} M_{\odot}$ to $10^{11.5} M_{\odot}$. Although their physical origin remains unclear, these low--dark matter regions are clearly indicated by the data. Our results provide an important observational benchmark for future hydrodynamical simulations that explore alternative dark matter models and feedback processes.

astro-ph.GA↗
arXiv2026

Galactic HII regions in LAMOST Medium-Resolution Spectroscopic Survey of Nebulae

Based on LAMOST Medium-Resolution Spectroscopic Survey of Nebulae (MRS-N) data and WISE Galactic HII region catalog, we construct a sample of 280 Galactic HII regions and candidates in the Outer Galaxy (80$^{\circ}$ $\lesssim$ l $\lesssim$ 220$^{\circ}$). Using MRS-N optical spectra, we measure four emission lines (H$α$, [NII]$λ$6584, [SII]$λλ$6717,6731) and use line-ratios to spectroscopically confirm 255 HII regions, including 90 previously "Known" HII regions and 165 newly classified ones. We measure their $T_{\rm e}$, $n_{\rm e}$ and oxygen abundance, and determine distances via associated OB stars and the kinematic method. The sample spans $R_{\rm gal}$ from 8.16 to 15.36 kpc, enabling investigation of radial gradients in physical properties. We find [NII]/H$α$ and [SII]/H$α$ decrease with increasing $R_{\rm gal}$, while [SII]/[NII] remains nearly flat; these trends are quite different from diffuse ionized gas (DIG). We derive the $T_{\rm e}$ gradient of 344.530 $\pm$ 78.083 K kpc$^{-1}$, and the $\log n_{\rm e}$ gradient of -0.143 $\pm$ 0.041 cm$^{-3}$ kpc$^{-1}$. Oxygen abundance shows a steep slope of -0.044 $\pm$ 0.010 dex kpc$^{-1}$ in the inner disk and a shallow slope of -0.016 $\pm$ 0.005 dex kpc$^{-1}$ in the outer disk, with a global slope of -0.014 $\pm$ 0.005 dex kpc$^{-1}$. We also examine the two-dimensional distributions of $T_{\rm e}$, $n_{\rm e}$, and oxygen abundance, and find the gradients vary with azimuth. There is no obvious difference between spiral arm and interarm regions, and no trend appears along individual arms. From [NII]/H$α$-[SII]$λ$6717/H$α$ diagram, HII regions have a S$^+$/S ratio (0.32), lower than DIG (0.43); however, heavy overlap prevents clear separation from this diagram alone.

astro-ph.GA↗
arXiv2026

The disrupted chemical enrichment history of the Milky Way driven by gas accretion

As the only galaxy enabling temporally-resolved observations from an internal vantage point, the Milky Way as a galaxy offers unique insights into galactic chemical enrichment history, establishment of fundamental scaling relations, and the underlying astrophysical processes. However, this insider perspective also introduces strong selection effects, hindering direct measurement of the Milky Way's global properties and comparison with the broader galaxy population, for the vast majority of which only integrated properties can be measured. {Here we report our measurements of the Milky Way's temporally-resolved galaxy-scale average metallicity using data from the APOGEE survey after correction for the selection function. Our findings unveil a present-day metallicity of the Milky Way close to the Sun, an interrupted integrated age-metallicity relation, and a disturbed evolutionary trajectory in the mass-metallicity diagram, likely caused by dilution and inside-out growth associated with external gas accretion around 7~Gyr ago. Our results highlight the critical role of gas accretion in disrupting the galactic enrichment histories and introducing scatter in mass-metallicity relations.

astro-ph.GA↗
arXiv2026

The FAST HI 21-cm Absorption Blind Survey. III. OH Absorption Search in the 21-cm Absorber Sample and Continued HI Absorption Search

We present the first blind search for OH 18-cm absorption with the Five-hundred-meter Aperture Spherical Telescope (FAST), conducted alongside the HI 21-cm absorption search. Our previous FAST blind HI absorption search identified 34 systems. In this work, we extend the search using 2024 and part of the 2025 CRAFTS and FASHI data (394.4 hr and 1622.1 deg$^{2}$) together with FATHOMER observations, yielding three known and four new HI absorbers, for a total of 41 HI absorption systems. We search for OH absorption in 19 HI absorption systems whose OH redshifted frequencies fall within the FAST band. The known OH absorber towards PKS 1413+135 was re-detected, making our survey the first blind survey to detect OH absorption. No new OH absorbers were identified. We examine the relationship between $N_{\rm{OH}}$ and $N_{\rm{HI}}$, applying survival analysis to account for upper limits. The analysis does not provide statistically significant evidence for either an $N_{\rm{OH}}$-$N_{\rm{HI}}$ correlation or redshift evolution of $N_{\rm{OH}}$/$N_{\rm{HI}}$. Finally, spectral stacking sets 3$σ$ OH column density upper limits of 4.93, 1.64, and 1.72 $T_{\rm{ex}}$/$c_{\rm{f,OH}}\times$10$^{12}$cm$^{-2}$K$^{-1}$ for associated, intervening, and combined samples, corresponding to [\rm{OH}]/[\rm{HI}] ratios of $<$1.66$\times$10$^{-8}$, $<$1.42$\times$10$^{-8}$, and $<$0.90$\times$10$^{-8}$, assuming $T_{\rm{ex}}$=10K for OH and $T_{\rm{s}}$=100K for HI. These results place the strongest constraints to date on the OH content in radio-selected HI absorbers and establish a blind-survey benchmark for future studies of molecular gas in HI-selected systems. They also demonstrate that known HI 21-cm absorbers provide an effective parent sample for systematic OH absorption searches, paving the way for future larger surveys.

astro-ph.GA↗
arXiv2026

High-Fidelity Mural Restoration via a Unified Hybrid Mask-Aware Transformer

Ancient murals are valuable cultural artifacts, but many have suffered severe degradation due to environmental exposure, material aging, and human activity. Restoring these artworks is challenging because it requires both reconstructing large missing structures and preserving authentic, undamaged regions. We present the Hybrid Mask-Aware Transformer (HMAT), a unified framework for high-fidelity mural restoration that addresses both structural completion and authentic-region preservation. HMAT integrates Mask-Aware Dynamic Filtering for robust local texture modeling with a Transformer bottleneck for long-range structural inference, enabling recovery of continuous line patterns and coherent mural structures under irregular damage. To handle diverse degradation morphologies, we introduce a mask-conditional style fusion module that adapts the generative process according to the shape and extent of missing regions. We also propose a fidelity-oriented training objective that combines hole-normalized reconstruction, discriminator feature matching, and high-receptive-field perceptual supervision to improve damaged-region fidelity, texture consistency, and boundary quality. In addition, we analyze a Teacher-Forcing Decoder with hard-gated skip connections as a feature-space boundary-conditioning strategy. Experiments show that HMAT matches or outperforms representative convolutional, transformer-based, and edge-guided inpainting baselines, with especially strong gains in perceptual realism and severe-mask settings. Ablation studies further identify the proposed objective, MADF-based mask-aware encoding, and mask-conditioned synthesis as the main contributors to restoration quality. These results demonstrate that HMAT provides an effective and competitive solution for cultural heritage mural restoration.

cs.CV↗
arXiv2026

Weak Evolution of Cosmic Atomic Hydrogen over the Past 4.5 Billion Years

The cosmic star formation rate density (CSFRD) has declined sharply toward the present day, but the roles of the atomic and molecular gas reservoirs remain uncertain. We measure the cosmic HI density, $Ω_{\mathrm{HI}}$, over $0<z<0.41$ by combining HI spectra from the Five-hundred-meter Aperture Spherical Telescope with optical spectroscopy from the Dark Energy Spectroscopic Instrument for $\sim2.5$ million galaxies across $\sim12,000\,{\rm deg}^2$. We measure a raw decrease in $Ω_{\mathrm{HI}}$ by a factor of $1.35\pm0.10$ over the past 4.5 Gyr. Even after applying the conservative systematic corrections from our forward model, the inferred decline is only $1.12\pm0.10$ -- still far weaker than the CSFRD decline (a factor of 2.46). The molecular gas density, in contrast, is known to evolve more closely with star formation. At fixed stellar mass, the average HI gas fraction evolves by less than 0.2 dex, showing that the weak evolution is present across the galaxy population. These quantitative differences rule out rapid depletion of galaxy HI as the primary driver of the late-time CSFRD decline, and provide a stringent benchmark for models of gas accretion, phase conversion and star-formation regulation.

astro-ph.GA↗
arXiv2026

Analytical and fitting formulae for solutions to Lyman-alpha radiative transfer equations: the effects of geometry, recoil, and velocity gradients

Lyman-alpha (Ly$α$) radiative transfer (RT) is important in many astrophysical environments and governed by multiple physical processes. In this paper, we provide analytical formulae/procedures for the solutions to Ly$α$ RT equations under three simple geometrical symmetries and investigate the effects of atomic recoil and gas bulk motion. We first study Ly$α$ spectra by solving Ly$α$ RT equations for a static, uniform gas cloud under cylindrical geometry. The solution is verified through Ly$α$ Monte Carlo RT simulations, and compared to those under slab and spherical geometries in literature. Second, to characterise the recoil effect, we empirically modify recoil-free Ly$α$ spectra. The method is motivated by Ly$α$ RT equations with recoil and justified by simulations. Finally, we account for constant velocity gradients in Ly$α$ RT equations and obtain series solutions for Ly$α$ spectra. The solutions demonstrate good agreement to Ly$α$ spectra from simulations for small velocity gradients (i.e. edge velocity $v_{\rm E}$ of a cloud being comparable to the thermal velocity $b$) but become less accurate for large ones. To characterise Ly$α$ spectra under large velocity gradients, we empirically extend the functional form of solutions and constrain them from fitting simulated Ly$α$ spectra. The resulting fitting formulae show significant improvement for large velocity gradients ($v_{\rm E}/b \sim 100$) under large optical depths. The analytical study of Ly$α$ spectra in this work completes the set of solutions under simple geometries, provides physical insights for Ly$α$ RT under recoil and velocity gradient, and develops analytical tools for theoretical studies that require inputs from Ly$α$ RT.

astro-ph.GA↗
arXiv2026

LGMT: Logic-Grounded Metamorphic Testing for Evaluating the Reasoning Reliability of LLMs

Large Language Models (LLMs) achieve strong performance on logical reasoning benchmarks, yet their reliability remains uncertain. Existing evaluations rely on static benchmarks, which fail to assess robustness under logically equivalent transformations and often overestimate reasoning capability. We propose LGMT (Logic-Grounded Metamorphic Testing), an oracle-free framework that leverages first-order logic (FOL) to evaluate LLM reasoning. By deriving metamorphic relations from formal logical equivalences, LGMT constructs semantically invariant test cases and detects reasoning defects through cross-case consistency checking. Experiments on six state-of-the-art LLMs show that LGMT exposes substantial hidden defects missed by traditional reference-based evaluations. We further find that models are particularly sensitive to symbol-level and conclusion-level variations, and that advanced prompting such as Few-shot CoT only partially mitigates these issues. These results suggest that LLM evaluation should move beyond isolated correctness toward robustness under logical invariance. LGMT provides a principled and scalable approach for diagnosing reasoning failures.

cs.AI↗
arXiv2026

Failure-Based Testing for Deep Reinforcement Learning Agents

Deep Reinforcement Learning (DRL) agents have been widely adopted across diverse domains to address challenging decision-making problems, such as autonomous driving and robotic control. Given that many of these applications are safety- and security-critical, rigorous testing of DRL agents is indispensable. Existing testing methods are typically guided by reward signals to detect failures. However, for well-trained agents, whose performance approaches optimal levels in standard operating conditions, reward signals remain generally high, making current methods ineffective at uncovering critical failures. To address these challenges, we propose a novel failure-based method that leverages task-induced failure insights to enhance failure detection capability while reducing the number of tests required. Since DRL agents are inherently designed with human-defined tasks, they provide valuable cues about task difficulty. Intuitively, a DRL agent is more likely to fail when confronted with a more difficult task; therefore, PRT prioritizes these tasks. Building on this foundation, we propose Prior Random Testing, a black-box failure-based testing method that enables targeted prioritization while preserving the diversity of generated test cases. Guided by task-induced failure insights, PRT prioritizes failure-prone regions of the input domain, thereby facilitating efficient failure detection. PRT is evaluated on four widely used benchmarks and compared with different state-of-the-art methods including fuzzing, search-based and generative-based methods. PRT ranks among the top performers in terms of both the cost of finding the first failure and the diversity of test cases. Notably, compared to random testing, PRT achieves better diversity and reduces the testing cost by over 50%.

cs.SE↗
arXiv2026

Measurements of quasar proximity zones with the Ly$α$ forest of DESI Y1 quasars

The intergalactic medium (IGM) around quasars is shaped by their dense environments and by their excess ionizing radiation, forming a "quasar proximity zone" whose size and anisotropy depend on the quasar's halo mass, luminosity, age, and radiation geometry. Using over 10,000 quasar pairs from the Dark Energy Spectroscopic Instrument (DESI) Year 1 data, with projected comoving separations $r_{\perp} < 2\,h^{-1}{\rm Mpc}$, we investigate how the proximity zone of foreground quasars at $z\sim2{\rm-}3.5$ affects Lyman-alpha absorption in their background quasars. The large DESI sample enables unprecedented precision in measuring this "transverse proximity" effect, allowing a detailed investigation of the signal's dependence on the projected separation of quasar pairs and the luminosity of the foreground quasar. We find that enhanced gas clustering near quasars dominates over their ionizing effect, leading to stronger absorption on neighboring sightlines. Under the assumption that quasar ionizing luminosity is isotropic and steady, we infer the IGM overdensity profile in the vicinity of quasars, finding overdensities as high as $Δ\sim 10$ at comoving distance $\sim 1\,h^{-1}{\rm Mpc}$ from the most luminous systems. Surprisingly, however, we find no significant dependence of the proximity profile on the luminosity of the foreground quasar. This lack of luminosity dependence could reflect a cancellation between higher ionizing flux and higher gas overdensity, or it could indicate that quasar emission is highly time variable or anisotropic, so that the observed luminosity does not trace the ionizing flux on nearby sightlines.

astro-ph.GA↗
arXiv2026

A Spatially Resolved HI Survey of Seyfert Galaxies: the Role of AGN Feedback in Shaping Atomic Gas Reservoirs

Active galactic nucleus (AGN) feedback is a key ingredient in galaxy evolution, yet its impact on the cold atomic gas reservoir -- the neutral hydrogen (HI) phase -- remains poorly constrained. We present the most extensive spatially resolved HI 21-cm survey of Seyfert AGN hosts to date, based on observations with the Giant Metrewave Radio Telescope (GMRT). Our high-resolution HI maps of eight Seyfert galaxies reveal detailed kinematics and surface density distributions of their atomic gas disks. We find that AGN-host galaxies exhibit a slightly shallower HI mass-size relation than the canonical relation or the SIMBA simulation predictions; however, the measured slope remains consistent with the canonical value within $2σ$ uncertainties. This result suggests that AGN feedback does not significantly disrupt the global extent or large-scale structure of atomic gas reservoirs. To investigate the internal HI kinematics in greater detail, we perform a 3D kinematic forward modeling of the HI disk in UGC 4503. Our analysis reveals an elevated intrinsic velocity dispersion of $σ= 14.9^{+6.1}_{-3.8}$ km/s and a reduced level of rotational support, with $V/σ= 14.28_{-4.17}^{+4.97}$, compared to large-sample star-forming spirals. These kinematic signatures, together with localized residuals in the velocity field, indicate that AGN-driven outflows or jets may inject or indirectly affect the turbulence in the atomic gas disk, potentially regulating the cold gas reservoir. Future GMRT observations, combined with optical integral-field spectroscopy from MaNGA, will enable quantitative constraints on the role of AGN feedback in regulating star formation efficiency across a larger and more representative galaxy sample.

astro-ph.GA↗
arXiv2026

Bidirectional Empowerment of Metamorphic Testing and Large Language Models: A Systematic Survey

Large language models (LLMs) have introduced substantial challenges to software quality assurance due to their generative, probabilistic, and open-ended nature, which intensifies the oracle problem and limits the applicability of traditional testing methods. Metamorphic testing (MT), which checks necessary relations among multiple related executions rather than relying on exact expected outputs, has emerged as a promising approach for testing LLMs and other oracle-deficient systems. At the same time, the strong semantic understanding, reasoning, and code generation capabilities of LLMs create new opportunities to automate the traditionally labor-intensive phases of MT. This survey systematically reviews 93 primary studies and characterizes this reciprocal relationship as the bidirectional empowerment of MT and LLMs. We propose a taxonomy spanning two complementary directions: MT for LLMs, which uses MT to verify, validate, assess, and understand LLMs and LLM-based systems across issues such as hallucination, fairness, robustness, code reliability, retrieval-augmented generation, dialogue, and autonomous agents; and LLMs for MT, which leverages LLMs to support metamorphic relation discovery, input transformation and synthesis, executable test implementation, and agentic closed-loop testing. By synthesizing these developments, this survey provides a structured foundation for understanding the evolving synergy between MT and LLMs and highlights future directions for building more rigorous, scalable, and trustworthy AI quality assurance methodologies.

cs.SE↗
arXiv2026

PCREQ: Automated Inference of Compatible Requirements for Python Third-party Library Upgrades

Python third-party libraries (TPLs) are essential in modern software development, but upgrades often cause compatibility issues, leading to system failures. These issues fall into two categories: version compatibility issues (VCIs) and code compatibility issues (CCIs). Existing tools mainly detect dependency conflicts but overlook code-level incompatibilities, with no solution fully automating the inference of compatible versions for both VCIs and CCIs. To fill this gap, we propose PCREQ, the first approach to automatically infer compatible requirements by combining version and code compatibility analysis. PCREQ integrates six modules: knowledge acquisition, version compatibility assessment, invoked APIs and modules extraction, code compatibility assessment, version change, and missing TPL completion. PCREQ collects candidate versions, checks for conflicts, identifies API usage, evaluates code compatibility, and iteratively adjusts versions to generate a compatible requirements.txt with a detailed repair report. To evaluate PCREQ, we construct REQBench, a real-world benchmark with 2,095 upgrade scenarios derived from 34 real-world scientific/ML Python projects. Results show PCREQ achieves a 94.03% inference success rate, outperforming PyEGo (37.02%), ReadPyE (37.16%), and LLM-based approaches (GPT-4o, DeepSeek V3/R1) by 18--22%. PCREQ processes each scenario from REQBench in 60.79 s on average, demonstrating practical efficiency. PCREQ reduces manual effort in troubleshooting upgrades, advancing Python dependency maintenance automation.

cs.SE↗
arXiv2026

Simultaneous Detection of High-Dimensional Entanglement for Two Unknown Quantum States

The state overlap, quantified via $\tr[ρσ]$, is a metric widely used to assess the closeness between two quantum states $ρ$ and $σ$. Although global state overlap alone does not directly capture entanglement properties, we uncover that incorporating local state overlaps provide profound insights into the entanglement characteristics of quantum states. To be precise, the ratio of global to local state overlaps provides a lower bound on the Schmidt number, which is usually used for quantifying high-dimensional entanglement. Unlike conventional methods for detecting entanglement, the approach here can simultaneously reveal entanglement information for two unknown quantum states. Moreover, state overlap can be efficiently determined through local randomized measurement methods, which ensures the experimental feasibility of our approach. In a special case, our criterion reduces to an entanglement criterion that is more powerful than the two criteria used most in experiment--the purity criterion and the fidelity-based criterion and also outperform the $p_3$-PPT method in specific instances. Our findings highlight a promising direction for advancements in entanglement detection experiments.

quant-ph↗
arXiv2026

A jet-gas interaction beyond the host galaxy: detection of a neutral hydrogen outflow at cosmic noon

We present upgraded Giant Metrewave Radio Telescope (uGMRT) observations of 0731+438, an \mbox{FR II} radio galaxy at a redshift of 2.429 with two lobes separated by 82 kpc. A blueshifted, faint and broad \mbox{H{\sc i}} 21 cm absorption line with velocity full width at half maximum (FWHM) $\sim 600\,\rm km\,s^{-1}$ is detected against the southern radio lobe that is 47 kpc from radio core, indicating a neutral hydrogen outflow associated with jet-gas interaction beyond the host galaxy. The outflow has a mass outflow rate of $\sim\,0.4T_{\rm s}Ω\rm\, M_\odot\,{\rm yr}^{-1}$, which could increase to $\sim\,4.0T_{\rm s}Ω\rm\,M_\odot\,{\rm yr}^{-1}$, corresponding to an energy outflow rate of $2.4T_{\rm s}Ω\times10^{40}$ -- $1.5T_{\rm s}Ω\times10^{41}\,\rm erg\,s^{-1}$, where $T_{\rm s}$ is the spin temperature and $Ω$ is the solid angle of the outflow. Previous optical observations identified an extended emission line region aligned with the radio axis, ionized by the central Active Galactic Nucleus (AGN). Within this region, a warm and ionized outflow with a mass outflow rate of $\sim\,50\rm\, M_\odot\,{\rm yr}^{-1}$ and an energy outflow rate of $\sim1.7\times10^{43}\,\rm erg\,s^{-1}$ was detected. We propose that both the extended emission line region and the optical outflow are results of synergistic effect between jet and AGN radiation. The AGN likely exerts negative feedback on the host galaxy, as evidenced by the gas expulsion by the jet and the high velocity dispersion of ionized gas observed optically. So far, detections of jet-driven neutral hydrogen outflows remain rare. The high redshift, large outflow radii, substantial mass outflow rate and energy outflow rate of the neutral hydrogen outflow in 0731+438 expand the known parameter space of such outflows.

astro-ph.GA↗
arXiv2026

Beyond Benchmarks of IUGC: Rethinking Requirements of Deep Learning Methods for Intrapartum Ultrasound Biometry from Fetal Ultrasound Videos

A substantial proportion (45\%) of maternal deaths, neonatal deaths, and stillbirths occur during the intrapartum phase, with a particularly high burden in low- and middle-income countries. Intrapartum biometry plays a critical role in monitoring labor progression; however, the routine use of ultrasound in resource-limited settings is hindered by a shortage of trained sonographers. To address this challenge, the Intrapartum Ultrasound Grand Challenge (IUGC), co-hosted with MICCAI 2024, was launched. The IUGC introduces a clinically oriented multi-task automatic measurement framework that integrates standard plane classification, fetal head-pubic symphysis segmentation, and biometry, enabling algorithms to exploit complementary task information for more accurate estimation. Furthermore, the challenge releases the largest multi-center intrapartum ultrasound video dataset to date, comprising 774 videos (68,106 frames) collected from three hospitals, providing a robust foundation for model training and evaluation. In this study, we present a comprehensive overview of the challenge design, review the submissions from eight participating teams, and analyze their methods from five perspectives: preprocessing, data augmentation, learning strategy, model architecture, and post-processing. In addition, we perform a systematic analysis of the benchmark results to identify key bottlenecks, explore potential solutions, and highlight open challenges for future research. Although encouraging performance has been achieved, our findings indicate that the field remains at an early stage, and further in-depth investigation is required before large-scale clinical deployment. All benchmark solutions and the complete dataset have been publicly released to facilitate reproducible research and promote continued advances in automatic intrapartum ultrasound biometry.

cs.CV↗
arXiv2026

Thermoelastic surface acoustic waves in low-loss silicon nitride integrated circuits

Acousto-optic modulation in photonic integrated circuits harness the applications that include signal processing, quantum photonics and microwave photonics. However, silicon nitride ($\rm{Si_3N_4}$), as a main-stream low-loss scalable photonic platform, suffers from the lack of piezoelectric effect and therefore the hybrid co-integration with other materials is always required for acousto-optic modulation. Here, we employed thermoelastic surface acoustic waves (SAW) in a 8 dB/m propagation loss $\rm{Si_3N_4}$ integrated circuits without adding extra materials. A phase modulation efficiency enhancement of 13.6 dB is realized with a multi-pass configuration. Furthermore, a single-sideband intermodal scattering with a suppression ratio of 8 dB is measured and an intensity modulation is observed by incorporating the phase modulation into a ring resonator spectral. This thermoelastic SAW technique, as an initial step of acousto-optic modulation in low-loss $\rm{Si_3N_4}$ platform, is promising for integrated microwave photonics and programmable photonics applications.

physics.optics↗
arXiv2026

Insights into the Physical Nature of Polar Ring Galaxies from H I Observations

Polar ring galaxies (PRGs) host an outer ring of gas and stars oriented nearly perpendicular to the main stellar body. They represent extreme examples of misaligned systems and provide valuable insight into galaxy interactions, gas accretion, and peculiar gas dynamics. We compile a complete sample of kinematically confirmed PRGs and collect their H I measurements. Combining literature data with new observations from FAST, we detect H I emission in 22 sources, identify one potential H I absorption feature, and find four non-detections among 40 confirmed PRGs. Compared to galaxies in the ALFALFA and xGASS surveys, PRGs predominantly occupy the green valley or quenched regimes but exhibit higher gas fractions than typical early-type galaxies, suggesting gas accretion. The H I profile asymmetry and shape for PRGs are not consistent with that of the ALFALFA sample with p<0.05. We examine their Tully-Fisher relation (TFR) and baryonic TFR (bTFR), linking the systems' rotation velocities to their masses. The extreme outliers in TFRs for the control sample tend to display single-peaked H I profiles. PRGs do not follow a tight TFR or bTFR if the H I resides primarily in the host galaxy. But the scatter decreases significantly if we assume the gas is mainly distributed in the polar ring. Spatially resolved H I observations are essential to disentangle the gas distribution and kinematics in PRGs, which are key to understanding their formation mechanisms.

astro-ph.GA↗