arXiv subjects

Zheng Cai

Publications and source records attributed to Zheng Cai.

At least 37 records · Page 2Linked to original sources

arXiv2026

A Post-starburst Galaxy Undergoing Ram-pressure Stripping at Redshift 3.06

Understanding how galaxies ignite and extinguish their star formation remains a cornerstone question in modern astrophysics. Recent JWST surveys have revealed an overabundance of massive quiescent galaxies in the first billion years of the Universe, challenging current models of galaxy evolution. In the nearby Universe, ram pressure stripping (RPS) is a major environmental mechanism capable of rapidly shutting down star formation, yet direct observation remains scarce at redshift $z\gtrsim1$, and its role at $z>2$ is even poorly constrained by simulations. Here, we utilize JWST and ALMA observations to present direct evidence of RPS in the post-starburst galaxy A2744-JF-z3, residing in a galaxy group at redshift 3.06, the earliest such detection to date. Spectroscopic diagnostics and spectral energy distribution modeling reveal the ongoing removal of cold gas and dust, coincident with the abrupt cessation of star formation. Contrary to hydrodynamical simulations that predict a reduced incidence of RPS at high redshift, our results instead imply that RPS can operate at $z>3$, suggesting a highly stochastic and impulsive stripping within a clumpy, filamentary intra-group and circumgalactic medium. These observations extend environmental quenching well into the epoch of galaxy assembly, highlighting RPS as a previously overlooked decisive pathway to rapid quenching in nascent groups and protoclusters in the early Universe.

astro-ph.GA↗

arXiv2026

(LRDs)$^2$: The Low-ReDshift Little Red Dots Survey. II. DESI DR1 Sample

JWST has revealed a substantial population of "Little Red Dots" (LRDs) at $z>4$, challenging conventional AGN frameworks. However, the low-redshift regime remains largely unexplored. In the second paper of the (LRDs)$^2$ series, we present a systematic selection from DESI DR1 and identify 27 LRDs at $z=0.2-0.9$, yielding a number density lower limit of $7.5 \times 10^{-10}$ cMpc$^{-3}$. We conducted near-IR spectroscopic follow-up observations for 18 of them, revealing their full SED shapes and emission lines. These low-$z$ LRDs share the hallmark properties of their high-$z$ counterparts: compact morphology, V-shaped UV-optical continua, broad Balmer emission with extreme decrements (median H$α$/H$β\sim 16$), frequent Balmer absorption (67%), and blackbody-like optical-to-near-IR continua. All have low metallicity, occupy the same regions in the BPT diagram as high-$z$ LRDs, and have softer ionizing spectra than typical AGNs. The consistency between low-$z$ and high-$z$ LRD properties indicates the same physical processes at work. The correlation between broad-line Balmer luminosity and $L_{5100}$ deviates from that of local type-1 AGNs, limiting the direct application of local BH mass calibrations. Ionized [O III] outflows are ubiquitous (78%). One LRD at $z=0.196$, J1717+3807, shows robust long-term variability in $i$ and WISE bands. The optical-to-NIR continua of LRDs reveal a wide range of temperatures $\sim 2000-4700$ K (peak $0.6-1.5$ $μ$m), with a subset showing cooler and larger envelopes than those at high $z$. Low-$z$ LRDs serve not only as proximate laboratories for probing the nature of LRDs, but also trace the cosmic evolution of this population from the cosmic dawn to the present day.

astro-ph.GA↗

arXiv2026

Revisiting the mass metallicity relation and the fundamental metallicity relation of dwarf galaxies at cosmic noon with NIRISS

We extend the stellar-mass gas-phase metallicity relation (MZR) at $z = 1.1-3.4$ down to the extremely low-mass regime using 183 galaxies with $\log(M_*/M_\odot) = 6.3-10.2$, based on deep JWST/NIRISS slitless spectroscopy from the NGDEEP program. The derived MZR is in excellent agreement with our previous result from 50 galaxies in the GLASS-JWST sample, underscoring the robustness and universality of this relation. Together, these datasets constitute the largest sample of dwarf galaxies yet obtained with NIRISS. The observed MZR slope, $β\simeq0.24\pm0.03$, remains constant across nearly four orders of magnitude in stellar mass. Analytical modeling of the metal-loading factor of outflows ($ζ_\textrm{out}$) indicates that, at $M_*\lesssim10^8M_\odot$, $ζ_\textrm{out}$ becomes progressively less dominant than the gas fraction ($μ_\textrm{gas}$) in regulating the MZR slope. Using this enlarged NIRISS sample, we further test the existence of the fundamental metallicity relation (FMR). We find no robust evidence for an additional SFR dependence beyond the MZR, nor any reduction in metallicity scatter when SFR is included. Examination of systematic uncertainties in \oh, $M_*$ and SFR suggests that the MZR slope ($β\sim0.22$) is robust, and that different assumptions about the strong-line calibrations or star-formation history (SFH) of the galaxies change the slope by less than 1-$σ$. At the current depth of the NIRISS data, evidence for an FMR among high-redshift dwarf galaxies remains inconclusive, highlighting the need for larger samples, and deeper observations.

astro-ph.GA↗

arXiv2026

Early Emergence of Environmental Effects: Accelerated Galaxy Assembly in a z=2.96 Protocluster in the COSMOS Field

The redshift range z=2-4 marks a critical transition in large scale structure formation, where the dynamically unrelaxed progenitors of local massive clusters undergo rapid stellar mass assembly. We report the discovery and physical characterization of a highly significant protocluster, PC J1001+0214, at z=2.96 within the COSMOS field. Leveraging the multi-wavelength COSMOS2025 catalog with exceptional photometric precision in conjunction with JWST/NIRCam wide-field slitless spectroscopy (WFSS) from the COSMOS-3D program, we robustly identify a cosmic overdensity with $δ=2.66$. The structure comprises 131 member galaxies, including 21 spectroscopically confirmed members (identified primarily via He I $\lambda10830$ emission) and 110 high-fidelity photometric members. A comparative analysis against a mass-complete coeval field sample reveals a statistically significant +0.2 dex shift in the stellar mass distribution of protocluster members, signaling accelerated mass assembly in the dense environment by $z\sim3$. While the protocluster population broadly follows the star-forming main sequence, low-to-intermediate mass galaxies ($\log_{10}(M_{*}/M_{\odot})\le9.7$) exhibit a measurable star formation rate (SFR) enhancement of +0.11 to +0.15 dex. Crucially, the quiescent fraction remains extremely low and indistinguishable from the field sample, implying that environmental quenching mechanisms have not yet become dominant. Furthermore, a preliminary size-mass analysis hints at elevated morphological compactness among protocluster members at fixed stellar mass. These results suggest that PC J1001+0214 represents a growth-dominated protocluster phase in which environmental effects are already detectable, primarily through accelerated stellar mass assembly and ongoing growth rather than through strong quenching.

astro-ph.GA↗

arXiv2026

From Large Telescopes to the MUltiplexed Survey Telescope (MUST)

Recent advances in astronomical observations have ushered in an era of remarkable discoveries. We now probe the Universe through multi-messenger signals, image the sky with unprecedented depth and resolution, and investigate individual sources using powerful large-aperture telescopes. Yet, a critical gap persists: the lack of wide-field, highly multiplexed spectroscopic capabilities needed to fully exploit the wealth of imaging data from current and upcoming surveys. In this review, we trace the historical development of large optical telescopes and spectroscopic surveys, assess the capabilities of ongoing and near-future facilities, and motivate the need for next-generation Stage-V spectroscopic experiments. As a representative example, we present the MUltiplexed Survey Telescope (MUST), the first Stage-V spectroscopic facility currently under construction. MUST is a 6.5-meter telescope designed to obtain optical spectra for over 20,000 targets simultaneously within a $\sim$5 deg$^2$ field, using a modular focal plane populated with 6.2-mm pitch fiber-positioning robots. Over an 8-year survey in the 2030s, MUST aims to build the most comprehensive 3D spectroscopic map of the Universe to date, measuring redshifts for over 100 million galaxies and quasars and opening new windows into cosmology, Galactic structure, and time-domain astrophysics.

astro-ph.IM↗

arXiv2026

Nonlinear Ohmic electromagnetic response

We systematically investigate nonlinear Ohmic responses in second-harmonic generation and bilinear magnetoelectric effects within the Matsubara Green's function formalism. The optical nonlinear Ohmic conductivity is shown to consist of a nonlinear Drude-like part and an intrinsic term determined by the fully symmetrized normalized quantum metric dipole. Notably, we predict a previously unrecognized intrinsic Ohmic conductivity arising from band geometry in the bilinear magnetoelectric response, which exhibits transverse behavior similar to its optical counterpart. Using a two-dimensional Dirac model, we demonstrate that this geometrically induced nonlinear Ohmic response is observable in materials with high Fermi velocity and narrow band gaps. Our work provides a systematic quantum field-theoretic framework for describing nonlinear Ohmic transport in condensed matter systems.

cond-mat.mes-hall↗

arXiv2026

MUltiplexed Survey Telescope (MUST) Science White Paper I: Overview of Large-Scale Structure Cosmology in the Era of Stage-V Spectroscopic Surveys

The MUltiplexed Survey Telescope (MUST) is a 6.5-meter telescope under development. Dedicated to highly-multiplexed, wide-field spectroscopic surveys, MUST observes over 20,000 targets simultaneously using 6.2-mm pitch positioning robots within a ~5 deg$^2$ field of view. MUST aims to conduct the first Stage-V spectroscopic survey in the 2030s, mapping the 3D Universe with over 100 million galaxies and quasars, spanning from the nearby Universe to a redshift of z ~ 5.5, corresponding to approximately 1 billion years after the Big Bang. To cover this extensive redshift range, we present an initial conceptual target selection algorithm for different types of galaxies, ranging from local bright galaxies and luminous red galaxies to emission-line galaxies, and high-redshift (2 < z < 5.5) Lyman-break galaxies. Using Fisher forecasts, we demonstrate that MUST can address fundamental questions in cosmology, including the nature of dark energy, tests of gravity theories, and investigations into primordial physics. This is the first paper in the series of science white papers for MUST, with subsequent developments focusing on additional scientific cases such as galaxy and quasar evolution, Milky Way physics, and dynamic phenomena in the time-domain Universe.

astro-ph.CO↗

arXiv2026

Deeper detection limits in astronomical imaging using self-supervised spatiotemporal denoising

The detection limit of astronomical imaging observations is limited by several noise sources. Some of that noise is correlated between neighbouring image pixels and exposures, so in principle could be learned and corrected. We present an astronomical self-supervised transformer-based denoising algorithm (ASTERIS), that integrates spatiotemporal information across multiple exposures. Benchmarking on mock data indicates that ASTERIS improves detection limits by 1.0 magnitude at 90% completeness and purity, while preserving the point spread function and photometric accuracy. Observational validation using data from the James Webb Space Telescope (JWST) and Subaru telescope identifies previously undetectable features, including low-surface-brightness galaxy structures and gravitationally-lensed arcs. Applied to deep JWST images, ASTERIS identifies three times more redshift > 9 galaxy candidates, with rest-frame ultraviolet luminosity 1.0 magnitude fainter, than previous methods.

astro-ph.IM↗

arXiv2026

Constraining the nature of active galactic nuclei through circumgalactic Lya emission at z=2-3

We present a comprehensive analysis of circumgalactic Lya nebulae around 59 unobscured and 26 obscured quasars at z=2-3, observed with the Keck Cosmic Web Imager (KCWI), to constrain the nature of active galactic nuclei (AGN) at cosmic noon. We find that Lya nebulae around unobscured quasars are significantly less symmetric having a symmetry parameter of a_w=0.2-0.6 and more spatially extended having a scale length of r_h=10.7+/-0.5 kpc than those around obscured quasars (a_w=0.6-0.8; r_h=6.6-7.7 kpc).Unobscured quasars also exhibit steeply declining velocity dispersion profiles with the slope of -4.3+/-0.4 km s^-1 kpc^-1, indicative of large-scale outflows, whereas obscured quasars display flat profiles (-0.2+/-0.7 and -0.6+/-0.4 km s^-1 kpc^-1). The degree of quasar obscuration appears to be intrinsically linked to nebular asymmetry and extent, a relationship that could be in tension with the standard orientation-based AGN unified model, as it expects unobscured-quasar nebulae to be more symmetric and compact. These results naturally fit the evolutionary scenario, where AGN feedback drives a transition from an obscured to an unobscured phase-progressively redistributing gas to larger radii, introducing anisotropy, and driving turbulence. Taken together, our findings favor the evolutionary scenario over the purely orientation-based unified model for quasars at cosmic noon.

astro-ph.GA↗

arXiv2026

Kernel-Smith: A Unified Recipe for Evolutionary Kernel Optimization

We present Kernel-Smith, a framework for high-performance GPU kernel and operator generation that combines a stable evaluation-driven evolutionary agent with an evolution-oriented post-training recipe. On the agent side, Kernel-Smith maintains a population of executable candidates and iteratively improves them using an archive of top-performing and diverse programs together with structured execution feedback on compilation, correctness, and speedup. To make this search reliable, we build backend-specific evaluation services for Triton on NVIDIA GPUs and Maca on MetaX GPUs. On the training side, we convert long-horizon evolution trajectories into step-centric supervision and reinforcement learning signals by retaining correctness-preserving, high-gain revisions, so that the model is optimized as a strong local improver inside the evolutionary loop rather than as a one-shot generator. Under a unified evolutionary protocol, Kernel-Smith-235B-RL achieves state-of-the-art overall performance on KernelBench with Nvidia Triton backend, attaining the best average speedup ratio and outperforming frontier proprietary models including Gemini-3.0-pro and Claude-4.6-opus. We further validate the framework on the MetaX MACA backend, where our Kernel-Smith-MACA-30B surpasses large-scale counterparts such as DeepSeek-V3.2-think and Qwen3-235B-2507-think, highlighting potential for seamless adaptation across heterogeneous platforms. Beyond benchmark results, the same workflow produces upstream contributions to production systems including SGLang and LMDeploy, demonstrating that LLM-driven kernel optimization can transfer from controlled evaluation to practical deployment.

cs.CL↗

arXiv2026

Pre-Virialized Assembly at Cosmic Dawn: The Dynamics and Extreme Ionization of Compact Group CGG-z7 at $z\sim7.04$

We report the discovery of CGG-z7, the most compact galaxy group at $z\gtrsim7$ identified to the north of the GOODS-North field, observed by the JWST POPPIES program. The system consists of at least six members within a projected size of $7.8\times5.7$ kpc$^2$, four of which are spectroscopically confirmed via [O III] and H$β$ emission. The group exhibits a low line-of-sight velocity dispersion ($\approx93.7$ km s$^{-1}$) relative to its substantial stellar mass ($M_* \approx 10^{9.8} M_{\odot}$), yielding a stellar-to-dynamical mass ratio of $M_*/M_{\mathrm{vir}} \approx 0.15$. This ratio, exceeding typical values for virialized halos by a factor of $3$, indicates that the system is highly likely not in dynamical equilibrium. Instead, we interpret CGG-z7 as a pre-virialized structure, likely a major merger caught near apocenter -- capturing the rapid, chaotic formation of a massive "Red Nugget". Spectroscopic analysis reveals extreme ionization conditions and low metallicity across the group. In particular, the central galaxy reaches an extraordinarily high [O III]/H$β$ ratio of $\sim18$, which is likely indicative of an obscured AGN. CGG-z7 thus serves as a unique laboratory for the physics of pre-virialized galaxy assembly, bridging the gap between turbulent high-$z$ assembly and the quiescent galaxies seen at cosmic noon.

astro-ph.GA↗

arXiv2026

Molecular Clouds Resolved at the Onset of Cosmic Noon

We present the discovery of seven molecular clouds in the radio galaxy B2 0902+34 at redshift z=3.4. These clouds are detected as CO(0-1) absorption features against the bright radio continuum, and spectrally resolved using the Karl G. Jansky Very Large Array (VLA). The velocity dispersion of the individual absorption components ranges from 3-7 km/s, which is similar to values observed for molecular clouds in the Milky Way and nearby galaxies, and imply cloud radii of R~10$^{1-2}$ pc. The absorbing clouds are found in a region of high obscuration inside a 30 kpc wide stellar nebula, as revealed by rest-frame near-ultraviolet imaging performed with the Hubble Space Telescope (HST). The fact that we spectrally resolve molecular clouds at the onset of Cosmic Noon opens prospects for studying cloud chemistry and physics that drive the formation of stars in the Early Universe.

astro-ph.GA↗

arXiv2026

The Cosmic Owl: Twin Active Collisional Ring Galaxies with Starburst Merging Front at $z=1.14$

Galaxy mergers play a critical role in driving galaxy evolution, especially by transforming galaxy morphology, redistributing gas around galaxies, triggering active galactic nuclei (AGN), and stimulating star formation. We present the Cosmic Owl, a galaxy merger at $z=1.14$, identified in the COSMOS field. Deep imaging and spectroscopy from JWST, ALMA, and VLA reveal a complex system of twin collisional ring galaxies, exhibiting nearly identical morphologies. The grism spectra from the JWST COSMOS-3D program confirm that both galaxies host an AGN. A bipolar radio jet from one AGN extends to strike the merging front. In addition, we detect a starburst at the merging front, characterized by luminous extended nebular line emission and a massive cold gas reservoir. This starburst is likely triggered by interstellar shocks induced by galaxy collision and the AGN jet. The twin ring structure of the Cosmic Owl requires further numerical simulations to clarify the precise conditions that lead to the formation of this rare morphology. This system exemplifies how shock-induced star formation, driven by galaxy collision or AGN jet, can act as a crucial mechanism for triggering intense starbursts in the early Universe.

astro-ph.GA↗

arXiv2026

MAMMOTH-LyC: Investigating the Role of Galaxy Mergers in a Strong Lyman Continuum Leaker at $z=2.39$

The MAMMOTH-LyC survey is a cycle 30 Hubble Space Telescope (HST) medium program obtaining 18-orbit-deep WFC3/UVIS F225W imaging in two massive galaxy protocluster fields at $z\sim2.2$. We introduce this survey by reporting the discovery of J1244-LyC1, a strong Lyman continuum (LyC) leaker at $z = 2.39$, exhibiting clear merger signatures. J1244-LyC1 has a highly significant ($10σ$) LyC detection, corresponding to an absolute escape fraction of $f_{\mathrm{esc}} \! =\!36\%\pm4\%$ ($1σ$). The LyC emission is spatially resolved into multiple peaks that coincide with the system's disturbed morphology, confirming genuine multi-site LyC leakage. With a stellar mass of $10^{10.2}{M_\odot}$, J1244-LyC1 is both the first confirmed high-redshift LyC-leaking merger and the most massive LyC emitter known to date. We interpret J1244-LyC1 as a merger-driven starburst system in which tidal interactions have disrupted the interstellar medium, creating multiple low-column-density pathways that facilitate LyC escape. This discovery provides the first direct evidence of spatially resolved LyC escape in a merging system, offering new insight into the potential role of major mergers in driving the cosmic reionization.

astro-ph.GA↗

arXiv2026

Can AI Dream of Unseen Galaxies? Conditional Diffusion Model for Galaxy Morphology Augmentation

Observational astronomy relies on visual feature identification to detect critical astrophysical phenomena. While machine learning (ML) increasingly automates this process, models often struggle with generalization in large-scale surveys due to the limited representativeness of labeled datasets, whether from simulations or human annotation, a challenge pronounced for rare yet scientifically valuable objects. To address this, we propose a conditional diffusion model to synthesize realistic galaxy images for augmenting ML training data (hereafter GalaxySD). Leveraging the Galaxy Zoo 2 dataset which contains visual feature, galaxy image pairs from volunteer annotation, we demonstrate that GalaxySD generates diverse, high-fidelity galaxy images that closely adhere to the specified morphological feature conditions. Moreover, this model enables generative extrapolation to project well-annotated data into unseen domains and advancing rare object detection. Integrating synthesized images into ML pipelines improves performance in standard morphology classification, boosting completeness and purity by up to 30% across key metrics. For rare object detection, using early-type galaxies with prominent dust lane features (~0.1% in GZ2 dataset) as a test case, our approach doubled the number of detected instances, from 352 to 872, compared to previous studies based on visual inspection. This study highlights the power of generative models to bridge gaps between scarce labeled data and the vast, uncharted parameter space of observational astronomy and sheds insight for future astrophysical foundation model developments. Our project homepage is available at https://galaxysd-webpage.streamlit.app/.

astro-ph.GA↗

arXiv2025

The Luminosity Function and Clustering of H$α$ Emitting Galaxies at $z\approx4-6$ from a Complete NIRCam Grism Redshift Survey

We study the luminosity function (LF) and clustering properties of 888 H$α$ emitters (HAEs) at $3.75 < z < 6$ in the GOODS-N field. The sample, built from JWST CONGRESS and FRESCO NIRCam grism surveys using a novel redshift assignment algorithm, spans $\sim$62 arcmin$^2$ and reaches $L_{\rm Hα} \sim 10^{41.2} {\rm erg s^{-1}}$. We identify two prominent filamentary protoclusters at $z \approx 4.41$ and $z \approx 5.19$, hosting 98 and 144 HAEs, respectively. The observed H$α$ LFs show similar shallow faint-end slopes for both protocluster and field galaxies at $z=3.75-5$, and for the protocluster at $z=5-6$ ($α\approx 1.2$ to $-1.3$). In contrast, the field LF at $z=5-6$ is much steeper ($α=-1.87_{-0.23}^{+0.30}$), suggesting that protocluster galaxies at $z > 5$ are more evolved, resembling those at $z=3.75-5$. The observed star formation rate density from H$α$, integrated down to 0.45 ${\rm M_\odot yr^{-1}}$, is $0.050^{+0.002}_{-0.003}$ and $0.046^{+0.006}_{-0.004} M_\odot {\rm yr}^{-1} {\rm Mpc}^{-3}$ at $z=3.75-5$ and $z=5-6$, with protoclusters contributing $\sim$25% and 55%, respectively. This implies that a large fraction of star formation at $z > 4$ occurs in protoclusters. We conduct the first star-formation-rate-limited 3D clustering analysis at $z > 4$. We find the filamentary protocluster geometry flattens the power-law shape of the HAE auto-correlation functions, with slopes much shallower than typically assumed. The auto-correlation function of field HAEs have correlation lengths of $r_0 = 4.61^{+1.00}_{-0.68} h^{-1}{\rm Mpc}$ at $z \approx 4-5$ and $r_0 = 6.23^{+1.68}_{-1.13} h^{-1}{\rm Mpc}$ at $z=5-6$. Comparing the observed correlation functions with the UniverseMachine simulation, we infer the dark matter (sub-)halo masses of HAEs to be $\log (M_h/M_\odot)=11.0-11.2$ at $z\approx 4-6$, with a scatter of 0.4 dex.

astro-ph.GA↗

arXiv2025

The Large-scale Environments of Low-luminosity AGNs at $3.9 < z < 6$ and Implications for Their Host Dark Matter Halos from a Complete NIRCam Grism Redshift Survey

We study the large-scale environments and clustering properties of 28 low-luminosity AGNs at $z=3.9-6$ in the GOODS-N field. Our sample, identified from the JWST NIRCam Imaging and WFSS data in CONGRESS and FRESCO surveys with either broad H$α$ emission lines or V-shape continua, are compared to 782 H$α$ emitters (HAEs) selected from the same data. These AGNs are located in diverse large-scale environments and do not preferentially reside in denser environments compared to HAEs. Their overdensity field, $δ$, averaged over (15 $h^{-1}$cMpc)$^3$, ranges from $-0.56$ to 10.56, and shows no clear correlation with broad-line luminosity, black hole (BH) masses, or the AGN fraction. It suggests that $> 10$ cMpc structures do not significantly influence BH growth. We measure the two-point cross-correlation function of AGNs with HAEs, finding a comparable amplitude to that of the HAE auto-correlation. This indicates similar bias parameters and host dark matter halo masses for AGNs and HAEs. The correlation length of field AGNs is 4.26 $h^{-1}$cMpc, and 7.66 $h^{-1}$cMpc at $3.9 < z < 5$ and $5 < z < 6$, respectively. We infer a median host dark matter halo mass of $\log (M_h/M_\odot)\approx 11.0-11.2$ and host stellar masses of $\log (M_\star/M_\odot) \approx 8.4-8.6$ by comparing with the UniverseMachine simulation. Our clustering analysis suggests that low-luminosity AGNs at high redshift reside in normal star-forming galaxies with overmassive BHs. They represent an intrinsically distinct population from luminous quasars and could be a common phase in galaxy evolution.

astro-ph.GA↗

arXiv2025

The Discovery of Little Red Dots in the Local Universe: Signatures of Cool Gas Envelopes

JWST observations have revealed a population of high-redshift "little red dots" (LRDs) that challenge conventional AGN models. We report the discovery of three local LRDs at $z = 0.1$-$0.2$, initially selected from the SDSS database, with follow-up optical/near-IR spectroscopy and photometry. They exhibit properties fully consistent with those of high-redshift LRDs, including broad hydrogen and helium emission lines, compact morphologies, V-shaped UV-optical SED, declining near-IR continua, and no significant variability. Two sources were targeted but not detected in X-rays with statistical significance. All three sources show blue-shifted He I absorption, while two exhibit H$α$ and Na D absorption lines. We detect full Balmer and Paschen line series in all three objects, along with abundant narrow [Fe II] emission in two. The emission line analyses suggest narrow lines originate from AGN-powered, metal-poor regions with minimal dust; broad lines come from inner regions with exceptionally high density or atypical dust properties; and [Fe II] emission arises from dense gas between broad and narrow-line regions. One of our objects, J1025+1402 (nicknamed $The~Egg$), shows extremely high equivalent width Na D, K I, and Ca II triplet absorption lines, along with other potential low-ionization absorption features, suggesting the presence of a cool ($\sim$5000 K), metal-enriched gas envelope. The optical/near-IR continua of these LRDs are also consistent with theoretical models featuring an atmosphere around black holes. The WISE-detected IR emission is consistent with weak dust emission of $T \sim 10^2-10^3$ K. We propose a conceptual model consisting of a largely thermalized cool-gas envelope surrounding the central black hole and an extended emission line region with high-density outflowing gas to explain the observed properties of these local LRDs.

astro-ph.GA↗