arXiv subjects

Zheng Cai

Publications and source records attributed to Zheng Cai.

At least 19 recordsLinked to original sources

arXiv2026

AEON-z5: A Candidate AGN-driven Outflow Enriching the Circumgalactic Medium at $z\simeq5.23$

The dispersal of chemically enriched gas from galaxies into their surroundings is a key process in galaxy evolution, yet direct observational evidence at z>5 remains scarce. We present AEON-z5, a galaxy at z~5.23 in the COSMOS field comprising a compact continuum-emitting core surrounded by an extended, line-dominated ionized nebula. JWST/NIRCam imaging shows that H$\alpha$+[N II] and H$\beta$+[O III] emission extends to projected radii of >4 kpc - 2-2.5 times the typical effective radius at the host stellar mass - reaching the outer ISM and the inner CGM. F444W grism data reveal a highly asymmetric H$\alpha$+[N II] profile, which we interpret as a bipolar outflow and decompose into three kinematic components. The dominant component has a flux-weighted velocity offset of ~+489 km/s and FWHM~630 km/s, with a wing reaching $v_{84}$~792 km/s. A tentative detached feature at $\Delta v_{LOS}$~2800 km/s, detected at 1.5$\sigma$ in the 1D spectrum (2.4$\sigma$ in the 2D fit), may trace an outflow clump. These kinematics are most coherently explained by an AGN in the core. For the extended nebula, we derive a velocity curve shifting redward with radius, reaching 200-400 km/s at $r_p$~1.3-2.5 kpc - a trend that may reflect an accelerating outflow, corotating gas, or recycled inflow viewed in projection. Crucially, the measured [N II]/H$\alpha$ ratios imply near-solar N2-based abundances (0.7-1.0 $Z_\odot$), remaining >0.37 $Z_\odot$ after allowing for AGN excitation and calibration systematics. The combination of large extent, enrichment, and extreme kinematics identifies AEON-z5 as a candidate snapshot of feedback-driven metal transport, offering a direct view of how early AGN activity may redistribute chemically processed gas into the CGM within the first ~1.1 billion years.

astro-ph.GA↗

arXiv2026

Imaging Stars at the Quantum Compatibility Limit

Imaging astrophysical sources with a multi-station interferometer is intrinsically a multiparameter quantum-estimation problem. {Using tools from multiparameter quantum metrology,} we show that time-resolved repetitive or adaptive measurements in an $N$-station array suffer a fundamental array-level incompatibility among visibility estimators. Collective measurements, {which coherently process the received starlight across multiple time bins in a single joint readout}, remove the array-size penalty up to an order-unity factor, yielding an asymptotic $O(\sqrt{N})$ enhancement for the {directional-averaged} SNR of visibility measurement. We then propose a memory-assisted interferometric architecture designed to implement collective readout through coherent storage and joint quantum processing. Imaging simulations and Fisher-information analyses demonstrate that collective measurements improve image reconstruction in near-term arrays and enhance the resolving power of future long-baseline architectures, with pronounced benefits for representative AGN targets such as NGC~4151 and 3C~273. These results highlight collective measurement as a promising building block for future quantum-assisted interferometric arrays for stellar imaging.

quant-ph↗

arXiv2026

Indirect evidence of the $2175\,\mathring{\mathrm{A}}$ extinction bump within the dusty torus of SDSS J141945.50+524648.0

We present a multi-wavelength study of the quasar SDSS J141945.50$+$524648.0 ($z=1.1599$), a member of the newly identified population of quasar-associated $2175\,\mathring{\mathrm{A}}$ dust absorbers. Utilizing JWST/NIRCam observations from the SAPPHIRES survey and archival data, we analyze the prominent $2175\,\mathring{\mathrm{A}}$ extinction bump detected in this object. The bump parameters are highly consistent with the Milky Way extinction curve, implying similar dust properties. Spectral analysis reveals a $\mathrm{Mg\,II}$ absorption doublet near the systemic velocity. Joint fitting of the $\mathrm{Mg\,II}$ and $\mathrm{Fe\,II}$ absorption lines favors a partial-covering model, yielding $C_{f,\rm BEL}=0.11^{+0.12}_{-0.07}$. Together with the small velocity offset ($\Delta v\approx96~{\rm km\,s^{-1}}$), these results favor an intrinsic absorber rather than an intervening system. Infrared SED modeling and double-peaked $\mathrm{Pa\,\alpha}$ emission indicate consistent orientations of the dusty torus ($\theta\approx60^{+7}_{-8}$ deg) and accretion disk ($i=63.7^{+10.9}_{-7.8}$ deg), suggesting a rim-penetrating line of sight through the torus. This configuration naturally explains the infrared emission, continuum extinction, and associated $2175\,\mathring{\mathrm{A}}$ bump, although a contribution from the host-galaxy ISM cannot be excluded. If associated with the torus, the carbonaceous carriers of the $2175\,\mathring{\mathrm{A}}$ feature may survive the intense AGN radiation field through localized shielding in optically thick dusty clumps. These results highlight the role of viewing geometry and dust distribution in regulating dust survival in quasar environments.

astro-ph.GA↗

arXiv2026

Inflow-driven galaxy evolution - I. Revealing the physics of the fundamental metallicity relation

We present a unified physical framework for the fundamental metallicity relation (FMR), based on the mass-continuity equations. The FMR is not merely the anti-correlation between star formation rate (SFR) and gas metallicity ($Z_{\rm g}$) at fixed stellar mass ($M_\star$); it is a redshift-invariant surface in the $(M_\star,{\rm SFR},Z_{\rm g})$ space. We construct a minimal cosmological gas flow model, calibrated to reproduce the mass-metallicity relation, star-forming main sequence, and stellar-to-halo mass relation at $z=0-3$, and show that the FMR emerges as a prediction of the calibrated physics. Through controlled experiments that progressively simplify the model, we reveal that in a universe where both the star formation efficiency ($\epsilon$) and mass-loading factor ($\eta$) are constants, the FMR reduces to a universal scaling between $Z_{\rm g}$ and $M_\star/$SFR, whose shape traces the transition from inflow-driven regime to equilibrium. The specific parameterisation of the observed FMR is not a fundamental symmetry but a contingent consequence of how $\epsilon$ and $\eta$ depend on stellar mass and redshift. We show that the gaseous FMR (gFMR), defined in the $(M_\star,M_{\rm g},Z_{\rm g})$ space, is more fundamental than the standard FMR: in the inflow-driven limit, $Z_{\rm g}$ is proportional to $M_\star/M_{\rm g}$, and the approach to equilibrium is governed by $M_\star/M_{\rm g}$ and $\eta$ alone. We derive an analytic solution for an idealised version of the model that provides closed-form expressions relating $Z_{\rm g}$, $M_{\rm g}/M_\star$, and $\eta$, and show this framework accurately reproduces the cosmological gas flow model. By establishing the physical origin of the FMR and its connection to the more fundamental gFMR, we provide the theoretical foundation to turn metallicity scaling relations into precision probes of the baryon cycle over cosmic history.

astro-ph.GA↗

arXiv2026

Misaligned or chaotic? A strong break of axial symmetry in the local LRD J1025 revealed with VLT/FORS2 spectropolarimetry

Little Red Dots (LRDs) are compact active galactic nuclei (AGN) with unusual spectral energy distributions and broad Balmer emission, candidate signposts of rapid black-hole growth. We present VLT/FORS2 optical linear spectropolarimetry of the closest known LRD, SDSS J102530.29+140207.3, at z=0.1. In total light, we detect spatially extended narrow-H$\alpha$ emission, probably tracing the host galaxy. We measure a nearly grey continuum polarisation $p_{\rm cont}=1.53\pm0.04$(rand.)$\pm$0.20(syst.) per cent, while broad H$\alpha$ is less polarised, $p_{\rm H\alpha}=0.58-0.84$ per cent. We rule out polarisation by Milky Way dust and dilution by an unpolarised line. The polarised continuum with a depolarised line resembles local Seyfert-1 nuclei and favours a single dominant source over multi-source explanations. After Stokes-continuum subtraction, broad H$\alpha$ shows no blue-to-red swing, but there is a significant (48$\pm$4)$^\circ$ continuum-to-line offset in polarisation angle. This implies a break of axial symmetry inside this object, posing interesting geometrical challenges to all existing LRD models and frameworks. We discuss different possible origins of this symmetry break and possible paths to discriminate between them with future observations.

astro-ph.GA↗

arXiv2026

First-star imprints in a metal-poor galaxy overdensity near the end of reionization

The first generation of stars, known as Population III (Pop III), formed from primordial gas consisting solely of hydrogen and helium and is believed to have emerged only a few hundred million years after the Big Bang. Detecting the chemical enrichment of metal-poor circumgalactic gas offers a promising way to trace the enrichment signature of Pop III stars. Along the sightline to the quasar SDSS J0100+2802, a metal absorber at $z = 5.945$, showing over-abundant carbon and silicon compared to solar, has been reported to be consistent with the enrichment pattern of Pop III stars. With the James Webb Space Telescope, we report the discovery of an unusually metal-poor galaxy overdensity of 17 members (mean metallicity $\approx 3\%$ solar) near this metal absorber, which is $\sim 0.4$ dex more metal-poor than coeval galaxies in similarly overdense environments. This less chemically evolved system may have provided favorable conditions for preserving the absorption signatures of Pop III enrichment. We infer a minimum dark matter halo of $\log(M_{\mathrm{h,min}}/M_{\odot})=10.68^{+0.93}_{-1.72}$, supporting late-time Pop III formation at the outskirts of atomic hydrogen cooling halos. Our findings open a promising observational pathway to identify the chemical imprints of the first stars and constrain the conditions for their formation.

astro-ph.GA↗

arXiv2026

A massive barred spiral galaxy at z = 5.102 discovered by JWST

We report M1149-BSG-z5, a barred spiral galaxy at $z = 5.102$, identified in the parallel field of MACS J1149+2223 with JWST and HST. M1149-BSG-z5 is the highest redshift barred galaxy candidate to date. Both isophote ellipse fitting and structural modeling support a stellar bar of length $a_\mathrm{bar} \approx 4.5$ kpc, and extended spiral arms peaking at $r \approx 5.5$ kpc. M1149-BSG-z5 is a massive main sequence star-forming galaxy, with a stellar mass of $10^{10.45}\rm M_\odot$ and a star-formation rate of $144\,\rm M_\odot/yr$. A concentrated bulge is embedded in an extended disk with a global S\'ersic index $n = 2.37$. With an effective radius of $R_{e} = 2.61\rm \ kpc$, M1149-BSG-z5 is larger than typical galaxies at $z \sim 5$ and comparable to barred galaxies at $2 < z < 4$. M1149-BSG-z5 also hosts a broad-line AGN, with a relatively low black-hole-to-stellar mass ratio of $\rm M_{\rm BH}/M_\ast\sim10^{-3}$. Its metal-enriched emission-line properties indicate that it is already chemically evolved. These properties imply M1149-BSG-z5 as an early-assembled and structurally evolved galaxy. We also find that M1149-BSG-z5 resides in an overdense region with a nearby companion galaxy, suggesting an interaction-driven bar formation mechanism. Its concentrated light, early assembly and main-sequence star formation also suggest baryon-dominated, gas-rich conditions, where gravitational instability can further accelerate the bar formation.

astro-ph.GA↗

arXiv2026

A Strongly Lensed Ultra-faint Arc at $z \approx 10$ with an F200W excess in Abell S1063

Strong gravitational lensing provides a powerful route to probing intrinsically faint galaxies during the first few hundred million years of cosmic history. In this Letter, we report the identification of GAR10, a highly magnified F115W-dropout galaxy at $z\approx10$ in the Abell S1063 cluster field, using deep JWST/NIRCam imaging from the GLIMPSE and GO-1840 programs. The source shows an unusually blue ultraviolet (UV) continuum and a significant F200W excess relative to adjacent bands. Under our high-magnification lensing solution, we infer a median magnification of $\mu=43^{+78}_{-20}$, corresponding to an intrinsic UV magnitude of $M_{\rm UV}\approx-15.8$. We use exploratory Prospector SED modeling to examine two physically motivated interpretations of the observed photometry. In Case I, GAR10 is described by an extremely metal-poor, continuum-dominated stellar population at $z=10.75_{-0.34}^{+0.41}$, with a blue UV slope of $\beta=-2.92\pm0.12$ and a low metallicity of $\log(Z/Z_\odot)=-3.56_{-0.85}^{+0.65}$, consistent with an extremely metal-poor or Pop III-like continuum-dominated interpretation under the adopted priors. In Case II, GAR10 is interpreted as an extremely young (1--3 Myr), high-ionization galaxy at $z=10.45_{-0.21}^{+0.11}$, in which the F200W excess is produced by intense rest-frame UV emission lines, including CIV, HeII, and CIII]. Both cases can partially reproduce the current photometry within the adopted priors, but they imply distinct ionizing sources, enrichment histories, and possible contributions to cosmic reionization. GAR10 therefore represents a rare laboratory for studying ultra-faint galaxy formation at cosmic dawn. Future JWST/NIRSpec spectroscopy will be essential to distinguishing between the steep continuum and emission-line origins of the F200W excess.

astro-ph.GA↗

arXiv2026

A Steep-Extinction Quasi-stellar Object at z=4.6: JWST Evidence for Abundant Small Dust Grains

The rapid accumulation of massive dust reservoirs in the early Universe remains a major challenge in astrophysics. While core-collapse supernovae can inject large dust grains ($a \gtrsim 0.1\,\mu{\rm m}$) on short timescales, explaining the total dust budgets in the early Universe likely requires efficient grain growth in the interstellar medium (ISM). Such growth depends critically on an abundant population of small grains, which maximize the surface area available for accretion and may be generated by rapid dust-processing or dust-formation channels. Here, we report the discovery of a QSO, UDS-27023, at $z=4.556\pm0.003$, identified using JWST/NIRSpec spectroscopy. By quantitatively comparing the spectra to QSO composite templates, we find that UDS-27023 displays an exceptionally steep far-UV extinction curve ($A_{1500}/A_V \approx 8$) but notably lacks the 2175 A bump ($A_\mathrm{bump}/A_V<0.34$ at $3\sigma$), indicating a dominance of small silicate dust grains. We interpret this phenomenology as evidence for active small-grain production and processing in the QSO environment. Mechanical shattering of pre-existing large grains by QSO-driven shocks and outflows provides one natural pathway, while in situ condensation of silicate grains inside dense QSO-driven winds may offer an additional route. Such a population of steep-extinction QSOs (SEQs) may therefore reveal a short-lived phase in which luminous active galactic nuclei generate, process, and redistribute small grains, potentially facilitating rapid ISM grain growth and enriching the circumgalactic medium.

astro-ph.GA↗

arXiv2026

Scalable All-Optical Fibre-Mode Data Transmission with Profiles-Preserved Decoding

Optical fibres are the primary medium for optical signal transmission, and their guided modes provide a high-dimensional basis for modal-domain information encoding. However, conventional demultiplexing approaches typically convert fibre modes into fundamental Gaussian modes and require repeated mode conversions, while existing profiles-preserved methods are generally restricted to fewer than three modes. High-quality fibre-mode data transmission therefore requires a scalable all-optical decoder capable of separating strongly overlapping modal channels while preserving their intrinsic spatial profiles. Here, we establish a scalable profiles-preserved all-optical decoding method for high-dimensional fibre-mode data transmission. By introducing a microlens-array-assisted decoding architecture with channel-dependent spherical phase compensation, the proposed method accommodates mode-dependent effective focal-length variations, enabling scalable modal-channel separation while preserving high-quality modal profiles at the output plane. Experimentally, the optical decoder resolved fields containing eight fibre modes, achieving a mode fidelity exceeding 0.72, a worst-channel crosstalk of $-5.57~\mathrm{dB}$ and a mean non-target crosstalk of $-21.34~\mathrm{dB}$, while reconstructing the relative modal weights with an error below 0.1. Semantic transmission experiments using digits and Chinese characters further demonstrated effective recovery of the encoded information from the decoded modal signals. We expect this work to provide a scalable route towards high-dimensional all-optical fibre-mode data transmission.

physics.optics↗

arXiv2026

MAMMOTH-Grism: Gas-phase Metallicity Gradients of Star-forming Galaxies in Protocluster Environments at Cosmic Noon

Environment plays a crucial role in shaping galaxy formation, yet the impact of overdensities on the internal chemical structure of galaxies at cosmic noon is still under debate. Here, we present spatially resolved gas-phase metallicity gradients for 42 star-forming galaxies in three massive protoclusters at $z \sim 2.3$, derived fromHubble Space Telescope (HST) slitless grism spectroscopy from the MAMMOTH-Grism survey. We find that the majority (29 of 42, $\sim$69%) of these protocluster members exhibit positive (inverted) metallicity gradients, a fraction significantly higher than observed in field galaxies of similar mass and redshift. By examining correlations with global properties, we show that these positive gradients are strongly associated with galaxies that are metal-deficient relative to the field mass-metallicity relation, particularly among the massive population ($\log(M_*/M_\odot) > 9.95$). These trends suggest that galaxies in dense protocluster environments experience substantial, enhanced inflows of pristine gas toward their central regions, which dilute the central metallicity and produce the observed inverted gradients. Our results provide observational evidence that environmental effects actively regulate gas accretion and chemical redistribution during the peak epoch of cosmic star formation.

astro-ph.GA↗

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, $\beta\simeq0.24\pm0.03$, remains constant across nearly four orders of magnitude in stellar mass. Analytical modeling of the metal-loading factor of outflows ($\zeta_\textrm{out}$) indicates that, at $M_*\lesssim10^8M_\odot$, $\zeta_\textrm{out}$ becomes progressively less dominant than the gas fraction ($\mu_\textrm{gas}$) 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 ($\beta\sim0.22$) 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-$\sigma$. 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

An Updated Characterization of Luminous Ly{\alpha} emitters at the End of Reionization

We present a multi-wavelength physical characterization of 14 luminous Ly$\alpha$ emitters (LAEs) at $z\approx6$, integrating deep ground-based Magellan/M2FS spectroscopy with heterogeneous JWST/NIRCam broad- and medium-band imaging. Identified via strong Ly$\alpha$ lines with extreme Ly$\alpha$ luminosities of ${>}10^{42.6}$ erg s$^{-1}$, the sample exhibits very large rest-frame equivalent widths (${\gtrsim}100$ \AA) and steeply blue UV continua ($\beta_{\rm median}\simeq-2.2$, $-18.2>M_{\rm 1500}>-20.2$ mag). Crucially, the integration of NIRCam medium-band photometry (F410M) breaks the degeneracy between strong rest-optical nebular emission and Balmer breaks, resolving prior mass overestimations. The tightly constrained spectral energy distribution modeling demonstrates that these luminous LAEs tend to be unequivocally low-mass, ultra-young dwarf starbursts; half the sample is characterized by stellar masses of $M_* < 10^8 M_{\odot}$, ages $\lesssim10$ Myr, and negligible dust attenuation. We also map the production efficiency of ionizing photons and Ly$\alpha$ escape fractions ($f_{\rm esc}^{\rm Ly\alpha}$). The $f_{\rm esc}^{\rm Ly\alpha}$ values are exceptionally high, with a median of ${\gtrsim}40$%, increasing for the bluer UV continua. Finally, analyzing spatial offsets between the Ly$\alpha$ centroid and the stellar counterpart, we demonstrate empirically that internal dust content, rather than neutral hydrogen gas, dominate the suppression of Ly$\alpha$ radiative transfer. Our study reveals that strong Ly$\alpha$ emission of the luminous LAEs are generally attributed to both the vigorous starburst activities and the high $f_{\rm esc}^{\rm Ly\alpha}$. Resembling Lyman continuum leakers, these extreme dwarf systems function as highly efficient ionizing engines at the conclusion of the Epoch of Reionization.

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↗