arXiv subjects

Min Du

Publications and source records attributed to Min Du.

At least 19 recordsLinked to original sources

arXiv2026

Gal3D: Superellipsoid Modeling of Radial 3D Galaxy Structure in IllustrisTNG and EAGLE Simulations

Galaxy morphology and structure are key tracers of galaxy formation and evolution, making accurate measurements of intrinsic three-dimensional (3D) shape essential for linking morphology to galaxy assembly and for comparing numerical simulations. We present Gal3D, a framework that reconstructs smoothed density fields from particle data and quantifies the radial 3D structure of simulated galaxies by fitting superellipsoids to iso-density surfaces. The method recovers axis ratios, orientations, center offsets, and superellipsoid indices ($S_a$, $S_b$, $S_c$), enabling a flexible characterization of diverse galactic structures such as disks, classical bulges, box/peanut bulges, and triaxial components. Applying Gal3D to galaxies in the IllustrisTNG and EAGLE simulations, we find that the radial extent of flattened disk regions increases with stellar mass up to $M_{*,30}\sim10^{11}\,M_\odot$ and then declines sharply, with EAGLE galaxies showing a saturation at $M_{*,30}\sim10^{10.5}\,M_\odot$. The bar-related $ \varepsilon_{ab}\equiv 1-b/a$ strengthens above $M_{*,30}\sim10^{10.5}\,M_\odot$ in both simulations, but remains systematically weaker in EAGLE. In TNG, outer bar regions are commonly associated with elevated $S_a$ and $S_c$, indicating enhanced boxiness and more prominent box/peanut-shaped bulges, whereas such higher-order signatures are weak or absent in EAGLE. At the highest stellar masses, flattened disks become less prominent, while inner prolate or triaxial structures remain common and massive EAGLE galaxies have more prolate or triaxial outer stellar bodies than their TNG counterparts. These results demonstrate that Gal3D provides a practical framework for quantifying intrinsic radial 3D structure and comparing morphology across cosmological simulations.

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

Exceptional Point Superradiant Lasing with Ultranarrow Linewidth

Achieving superradiant lasing with an ultranarrow linewidth is crucial for enhancing atomic clock stability in quantum precision measurement. By employing the exceptional point (EP) property of the system, we demonstrate theoretically superradiant lasing with linewidths in the $\mu$Hz range, sustained at the high-power level. This is achieved by incoherently pumping optical lattice clock transitions with ultracold alkaline-earth strontium-87 atoms in the EP of a $\mathcal{PT}$-symmetric system. Physically, the atomic coherence reaches a maximum in the EP, significantly amplifying the superradiance effect and resulting in superradiant lasing with an ultranarrow linewidth. This linewidth is even three orders of magnitude smaller than that of superradiant lasing in the systems without EP. Our work extends the realm of superradiant lasing by introducing the EP property, and offers promising applications for developing atomic clocks with exceptional stability and accuracy.

quant-ph↗

arXiv2026

PandaPose: 3D Human Pose Lifting from a Single Image via Propagating 2D Pose Prior to 3D Anchor Space

3D human pose lifting from a single RGB image is a challenging task in 3D vision. Existing methods typically establish a direct joint-to-joint mapping from 2D to 3D poses based on 2D features. This formulation suffers from two fundamental limitations: inevitable error propagation from input predicted 2D pose to 3D predictions and inherent difficulties in handling self-occlusion cases. In this paper, we propose PandaPose, a 3D human pose lifting approach via propagating 2D pose prior to 3D anchor space as the unified intermediate representation. Specifically, our 3D anchor space comprises: (1) Joint-wise 3D anchors in the canonical coordinate system, providing accurate and robust priors to mitigate 2D pose estimation inaccuracies. (2) Depth-aware joint-wise feature lifting that hierarchically integrates depth information to resolve self-occlusion ambiguities. (3) The anchor-feature interaction decoder that incorporates 3D anchors with lifted features to generate unified anchor queries encapsulating joint-wise 3D anchor set, visual cues and geometric depth information. The anchor queries are further employed to facilitate anchor-to-joint ensemble prediction. Experiments on three well-established benchmarks (i.e., Human3.6M, MPI-INF-3DHP and 3DPW) demonstrate the superiority of our proposition. The substantial reduction in error by $14.7\%$ compared to SOTA methods on the challenging conditions of Human3.6M and qualitative comparisons further showcase the effectiveness and robustness of our approach.

cs.CV↗

arXiv2026

Unifying the dynamical classification of early-type galaxies: kinematic deficits in IllustrisTNG versus observations

We conduct a comparative analysis of galaxy kinematics using IllustrisTNG simulations and integral-field spectroscopy (IFS) observations. We identify 2,342 early-type galaxies (ETGs) from the TNG100 simulation and 236 ETGs from the TNG50 simulation, comparing them with observations from MaNGA and ATLAS$^{3D}$. For these systems, we measure key kinematic parameters: the intrinsic spin parameter $\lambda_{R,\mathrm{intr}}$ (measured edge-on), the cylindrical rotational energy fraction $\kappa_{\mathrm{rot}}$, and structural mass ratios including the spheroid mass fraction $f_{\mathrm{spheroid}}$ and stellar halo mass fraction $f_{\mathrm{halo}}$. Our study reveals that standard classifiers--the $\lambda_{R}(R_e)=0.31\sqrt{\varepsilon}$ relation and $\overline{k_5}$ coefficient (higher-order Fourier term of velocity fields)--fail to align with observed kinematic bimodality. We propose revised thresholds: $\lambda_{R,\mathrm{intr}} \sim 0.4$, $\kappa_{\mathrm{rot}} \sim 0.5$, and $f_{\mathrm{spheroid}} \sim 0.6$, which classify galaxies into rotation-dominated (fast rotators) and random motion-dominated (slow rotators). Scaling relations from TNG enable observational estimates of $\kappa_{\mathrm{rot}}$ and $f_{\mathrm{spheroid}}$. The simulations exhibit a bimodality deficit, characterized by a lack of fast rotators and suppressed $\lambda_{R,\mathrm{intr}}$, attributed to excess galaxies with intermediate rotation and high spheroid/stellar halo mass. We introduce a novel method to estimate $f_{\mathrm{halo}}$ from IFS kinematics, though uncertainties remain.

astro-ph.GA↗

arXiv2026

Down-bending Breaks in Galactic Disks Are an Intrinsic Byproduct of Inside-out Growth

The exponential profile has long been hypothesized as the fundamental morphology of galactic disks. The IllustrisTNG simulations reproduce diverse surface-density profiles: Type I (single exponential), Type II (down-bending), and Type III (up-bending), consistent with observed mass-size relations and kinematics. Type II disks dominate the stellar-mass regime $M_\star < 10^{10.6} M_\odot$ with a prevalence of about 40%, exhibiting systematically extended morphologies. Conversely, Type III and Type I galaxies are more compact while following the same mass-size scaling relation. Evolutionary histories show that Type II galaxies experience minimal external perturbations, suggesting that Type II disks represent an intrinsic disk form and challenging conventional single-exponential paradigms. We demonstrate that Type II breaks arise naturally via inside-out growth since $z=1$, governed by synchronized cold-gas accretion and localized peaks in specific star formation rate. This mechanism also produces the characteristic U-shaped age profiles of Type II disks. Stellar dynamical redistribution plays a minor role in their formation.

astro-ph.GA↗

arXiv2025

GR-Dexter Technical Report

Vision-language-action (VLA) models have enabled language-conditioned, long-horizon robot manipulation, but most existing systems are limited to grippers. Scaling VLA policies to bimanual robots with high degree-of-freedom (DoF) dexterous hands remains challenging due to the expanded action space, frequent hand-object occlusions, and the cost of collecting real-robot data. We present GR-Dexter, a holistic hardware-model-data framework for VLA-based generalist manipulation on a bimanual dexterous-hand robot. Our approach combines the design of a compact 21-DoF robotic hand, an intuitive bimanual teleoperation system for real-robot data collection, and a training recipe that leverages teleoperated robot trajectories together with large-scale vision-language and carefully curated cross-embodiment datasets. Across real-world evaluations spanning long-horizon everyday manipulation and generalizable pick-and-place, GR-Dexter achieves strong in-domain performance and improved robustness to unseen objects and unseen instructions. We hope GR-Dexter serves as a practical step toward generalist dexterous-hand robotic manipulation.

cs.RO↗

arXiv2025

Cold Gas Infall onto A Brightest Group Galaxy via A Gas-Rich Minor Merger

Dust and cold gas are not uncommon in nearby early-type galaxies (ETGs), and represent an important aspect of their evolution. However, their origin has been debated for decades. Potential sources include internal processes (e.g., mass loss from evolved stars), external mechanisms (e.g., minor mergers or cooling flows), or a combination of both. Gas-rich minor mergers have long been proposed as an important channel for cold gas fueling in both observations and simulations, but direct evidence of cold gas transportation via gas-rich minor mergers remains elusive, particularly in galaxy groups and clusters where environmental effects are prevalent. In this letter, we present the first unambiguous case of direct cold gas transportation onto a brightest group galaxy (BGG) at $z=0.25$, driven by an ongoing close-separation gas-rich minor merger with a mass ratio of $\sim1:56$. High-resolution JWST imaging reveals a heavily obscured, low-mass satellite that is barely visible at restframe optical wavelengths. Tidal stripping from this satellite deposits gas and dust onto the BGG, forming prominent $\sim$10 kpc dust lanes in situ. Cosmological simulations indicate that such interactions preferentially occur in gas-rich satellites undergoing their first infall in highly eccentric orbits. Our results highlight the pivotal role of gas-rich minor mergers in replenishing cold gas reservoirs and shaping the evolution of central ETGs in galaxy groups.

astro-ph.GA↗

arXiv2025

Dexterous Teleoperation of 20-DoF ByteDexter Hand via Human Motion Retargeting

Replicating human--level dexterity remains a fundamental robotics challenge, requiring integrated solutions from mechatronic design to the control of high degree--of--freedom (DoF) robotic hands. While imitation learning shows promise in transferring human dexterity to robots, the efficacy of trained policies relies on the quality of human demonstration data. We bridge this gap with a hand--arm teleoperation system featuring: (1) a 20--DoF linkage--driven anthropomorphic robotic hand for biomimetic dexterity, and (2) an optimization--based motion retargeting for real--time, high--fidelity reproduction of intricate human hand motions and seamless hand--arm coordination. We validate the system via extensive empirical evaluations, including dexterous in-hand manipulation tasks and a long--horizon task requiring the organization of a cluttered makeup table randomly populated with nine objects. Experimental results demonstrate its intuitive teleoperation interface with real--time control and the ability to generate high--quality demonstration data. Please refer to the accompanying video for further details.

cs.RO↗

arXiv2025

Astra: Toward General-Purpose Mobile Robots via Hierarchical Multimodal Learning

Modern robot navigation systems encounter difficulties in diverse and complex indoor environments. Traditional approaches rely on multiple modules with small models or rule-based systems and thus lack adaptability to new environments. To address this, we developed Astra, a comprehensive dual-model architecture, Astra-Global and Astra-Local, for mobile robot navigation. Astra-Global, a multimodal LLM, processes vision and language inputs to perform self and goal localization using a hybrid topological-semantic graph as the global map, and outperforms traditional visual place recognition methods. Astra-Local, a multitask network, handles local path planning and odometry estimation. Its 4D spatial-temporal encoder, trained through self-supervised learning, generates robust 4D features for downstream tasks. The planning head utilizes flow matching and a novel masked ESDF loss to minimize collision risks for generating local trajectories, and the odometry head integrates multi-sensor inputs via a transformer encoder to predict the relative pose of the robot. Deployed on real in-house mobile robots, Astra achieves high end-to-end mission success rate across diverse indoor environments.

cs.RO↗

arXiv2025

Beyond Morphology: Challenges in Decomposing Massive Stellar Halos in Sombrero-like, Halo-Embedded Disk Galaxies

Sombrero-like galaxies exhibit unique structural properties that challenge traditional photometric decomposition methods. In this study, we investigate their structural differences using both photometric and kinematic approaches to assess the extent to which photometric decomposition may misidentify key components, particularly the stellar halo. We select 270 Sombrero-like galaxies at redshift z=0 from the TNG50 simulation, applying filters to include only those with stellar mass $M_{\ast} > 10^{10}M_{\odot}$ and stellar halo mass fraction $0.3 < f_{\rm halo} < 0.6$. Synthetic images are generated using the GALAXEV population synthesis code, and photometric decomposition is carried out on both face-on and edge-on views using GALFIT. We then compare these results with kinematic decomposition based on the auto-GMM method, focusing on differences in recovered structural parameters such as mass fractions and S'ersic indices.Sombrero-like galaxies typically consist of disks embedded in massive stellar halos and may account for 30-60% of galaxies in TNG50. However, their identification is complicated by structural degeneracies and the presence of disk features (e.g., bars, spirals, star formation) at low or moderate inclinations. In face-on projections, photometric decomposition systematically overestimates disk fractions as stellar halos are almost absent, while edge-on analysis provides only approximate halo fractions. Radial profiles show discrepancies between photometric and kinematic decomposition, particularly in central regions. Additionally, no conclusive link exists between the S'ersic index n and the presence of large stellar halos, challenging the use of n as a merger history proxy. These findings underscore the need for improved decomposition methods to better understand the complex structures of Sombrero-like galaxies.

astro-ph.GA↗

arXiv2025

Unveiling a young thick disk in the Milky Way

The thickness of a galaxy's disk provides a valuable probe of its formation and evolution history. Observations of the Milky Way and local galaxies have revealed an ubiquitous disk structure with two distinctive components: an old thick disk and a relatively young thin disk. The formation of this dual-disk structure and the mechanisms that develop the thickness of the disk are still unclear. Whether the disk thickness inherit from the birth environment or is established through secular dynamical heating after formation is under debate. In this work we identify a relatively young ($\sim$6.6 billion years old) geometric thick disk in the Milky Way, with a scale height of $0.64$ kpc at the Solar Circle. This young thick component exhibits comparable thickness and flaring strength to the canonical old thick disk but is more radially extended and systematically younger. We also identify thin disk components that formed before and after this young thick disk. Detailed analysis of the solar vicinity structure suggests that the young thick disk marks the onset of a new phase of upside-down disk formation. These findings strongly discount the role of secular dynamical heating and support a turbulent, bursty birth environment as the primary mechanism behind thick disk formation. The existence of two thick disk components suggests that the Milky Way has undergone at least two episodes of turbulent and bursty star formation, likely triggered by galaxy mergers.

astro-ph.GA↗

arXiv2025

Probing the Hot Gaseous Halo of the Low-mass Disk Galaxy NGC 7793 with eROSITA and Chandra

Galaxy formation models predict that local galaxies are surrounded by hot X-ray-emitting halos, which are technically difficult to detect due to their extended and low surface brightness nature. Previous X-ray studies have mostly focused on disk galaxies more massive than the Milky Way, with essentially no consensus on the halo X-ray properties at the lower mass end. We utilize the early-released eROSITA and archival Chandra observations to analyze the diffuse X-ray emission of NGC7793, a nearby spiral galaxy with an estimated stellar mass of only $3.2\times 10^9$ $M_{\odot}$. We find evidence for extraplanar hot gas emission from both the radial and vertical soft X-ray intensity profiles, which spreads up to a galactocentric distance of $\sim$ 6 kpc, nearly 30 $\%$ more extended than its stellar disk. Analysis of the eROSITA spectra indicates that the hot gas can be characterized by a temperature of $0.18^{+0.02}_{-0.03}$ keV, with 0.5--2 keV unabsorbed luminosity of $1.3\times 10^{38}$ erg $s^{-1}$. We compare our results with the IllustrisTNG simulations and find overall consistence on the disk scale, whereas excessive emission at large radii is predicted by TNG50. This work provides the latest detection of hot corona around a low-mass galaxy, putting new constrains on state-of-the-art cosmological simulations. We also verify the detectability of hot circumgalactic medium around even low-mass spirals with future high-resolution X-ray spectrometer such as the Hot Universe Baryon Surveyor.

astro-ph.GA↗

arXiv2025

The diverse physical origins of stars in the dynamically hot bulge: CALIFA vs. IllustrisTNG

We compare the internal stellar structures of central galaxies in the TNG50 and TNG100 simulations and field galaxies in the CALIFA survey. The luminosity fractions of the dynamically cold, warm, and hot components in both TNG50 and TNG100 galaxies exhibit general consistency with those observed in CALIFA galaxies. For example, they all exhibit a minimum luminosity fraction of the dynamically hot component in galaxies with intermediate stellar masses, and the morphology of each orbital component in the TNG50 and TNG100 galaxies closely resembles that found in the CALIFA galaxies. We therefore use the simulations to quantify the physical origins of the different components, focusing on the dynamically hot component in TNG50. We identify three primary regimes and thus physical processes: (1) in low mass galaxies that have not experienced major mergers, stars are born with a wide range of circularity distributions and have remained relatively unchanged until the present day. Consequently, hot stars in such galaxies at redshift 0 are predominantly born hot. (2) In higher mass galaxies lacking major mergers, most stars are initially born cold but are subsequently heated through secular evolution. (3) In galaxies across the entire mass range, mergers, if they occurred, significantly increased the hot orbital fraction. As a result, the dynamically hot bulge within $R_e$ of present-day galaxies does not indicate their past merger histories; instead, the hot stars in the outer regions are mostly heated or accreted by mergers, thus indicating galaxy merger history. The massive galaxies are initially born with cold, rotationally supported structures, consistent with recent observations from the James Webb Space Telescope (JWST) regarding high-redshift galaxies.

astro-ph.GA↗

arXiv2024

IllustrisTNG Insights: Factors Affecting the Presence of Bars in Disk Galaxies

Bars are important in the secular evolution of galaxies. This study is aimed at exploring the reasons why some galaxies have bars at redshift $z=0$ while others do not. We use ellipse fitting to measure the properties and evolution of bars in the IllustrisTNG cosmological simulation. By using the K-S two-sample test and tracing their evolutionary changes, we analyze the parameter differences between barred and unbarred galaxies. The properties of galaxies with short bars are also studied. When tracing all disk galaxies at $z=0$ back to $z=1$, all of them show similar bar features at $z=1$. The fraction of bars increases in barred and short-bar galaxies but decreases in unbarred galaxies during $z=1-0$. In the case of disk galaxies with stellar mass log$(M_*/M_\odot)> 10.8$, nurture (mainly mergers) plays the most important role in suppressing or destroying bars. Bars are more likely to endure in galaxies that experience fewer mergers, which can be quantified by smaller stellar halos and ex-situ mass fractions. Approximately 60\% of the unbarred galaxies in the local Universe once had a bar. In contrast, the lack of responsiveness to bar instabilities (a larger Toomre-Q parameter) due to a less compact nature plays an important role in generating unbarred disk galaxies with stellar mass log$(M_*/M_\odot)<10.8$. Moreover, short bars generally form at a similar time to normal bars, during which they either grow mildly or contract significantly. The fact that IllustrisTNG simulations produce too many galaxies with short bars indicates that the dynamical properties of the central regions in IllustrisTNG galaxies are less affected by external factors, such as mergers and gas inflows.

astro-ph.GA↗

arXiv2024

Two Channels of Metal-Rich Compact Stellar System Formation: Starbursts under High Ram Pressure versus Tidal Stripping

Most galaxies follow well-defined scaling relations of metallicity and stellar mass; however, some outliers at the low mass end of the observed galaxy population exhibit unusually high metallicity for their mass. Understanding how these objects get to be so metal-rich is vital for understanding the role of feedback in galaxy formation. Using the TNG50 simulation, we explore the origins of this phenomenon. We identify 227 metal-rich, compact stellar systems (CSSs) that deviate significantly from this scaling relation. These CSSs are satellites located in the vicinity of massive host galaxies, with stellar masses ranging from $10^{8} M_{\odot}$ to $10^{10}\ M_{\odot}$ (including six systems that are close analogs of the M31-M32 system). Contrary to the previously assumed scenario that such objects are predominantly products of tidal stripping, our results suggest a more prevalent role for ram pressure in their formation. Indeed, 76% (173) of these CSSs are formed through a burst of star formation occurring around the time of the first pericentric passage, typically at redshifts $z\lesssim1$, aided by strong ram pressure and tidal forces. The high ram pressure, resulting from the CSSs' rapid motion near the halo center, facilitates metal enrichment, producing high-metallicity CSSs by confining the metal-rich gas from bursty star formation, which leads to distinct stellar populations characterized by enhanced metallicity as well as high $\alpha$-abundance. Only the remaining 24% (54) of metal-rich CSSs are generated through the tidal stripping of massive progenitors. Our results further indicate that M32 is more likely to have formed through intense star formation events rather than through gradual, tidal stripping, thereby providing crucial insights into the nature of low mass, compact galaxy formation.

astro-ph.GA↗

arXiv2024

FACTS About Building Retrieval Augmented Generation-based Chatbots

Enterprise chatbots, powered by generative AI, are emerging as key applications to enhance employee productivity. Retrieval Augmented Generation (RAG), Large Language Models (LLMs), and orchestration frameworks like Langchain and Llamaindex are crucial for building these chatbots. However, creating effective enterprise chatbots is challenging and requires meticulous RAG pipeline engineering. This includes fine-tuning embeddings and LLMs, extracting documents from vector databases, rephrasing queries, reranking results, designing prompts, honoring document access controls, providing concise responses, including references, safeguarding personal information, and building orchestration agents. We present a framework for building RAG-based chatbots based on our experience with three NVIDIA chatbots: for IT/HR benefits, financial earnings, and general content. Our contributions are three-fold: introducing the FACTS framework (Freshness, Architectures, Cost, Testing, Security), presenting fifteen RAG pipeline control points, and providing empirical results on accuracy-latency tradeoffs between large and small LLMs. To the best of our knowledge, this is the first paper of its kind that provides a holistic view of the factors as well as solutions for building secure enterprise-grade chatbots."

cs.LG↗

arXiv2024

The evolutionary pathways of disk galaxies with different sizes

From the IllustrisTNG-50 simulation, a sample of 836 central disk galaxies with tiny stellar halos is chosen to study the inherent evolution of galaxies driven by nature. These galaxies are classified as compact, normal, or extended by referencing their locations on the mass-size ($M_\star-R_{\rm 1/2}$) diagram. This research demonstrates the distinctive evolutionary pathways of galaxies with different sizes in IllustrisTNG simulations, primarily driven by nature. It is confirmed that disk galaxies inherit the angular momentum of their parent dark matter halos. More compact galaxies form earlier within halos possessing lower specific angular momentum through heightened star formation during the early phase at redshifts above 2. During the later phase, the size of extended galaxies experiences more pronounced growth by accreting gas with high angular momentum. Additionally, we reveal that many key characteristics of galaxies are linked to their mass and size: (1) compact galaxies tend to exhibit higher metal content, proportional to the potential well $\frac{M_\star}{R_{\rm 1/2}}$, (2) compact galaxies host more massive bulges and black holes, and higher central concentration. Furthermore, our analysis indicates that galaxies of all types continue to actively engage in star formation, with no evident signs of quenching attributed to their varying sizes and angular momenta.

astro-ph.GA↗