Sazuna/UAT_keywords huggingface dataset:
Dark Gaps and Resonances in Barred Galaxies. Dark gaps, low surface brightness regions along the bar minor axis, are expected to form as a consequence of secular evolution in barred galaxies. Although several studies have proposed links between dark gap locations and dynamical resonances, the results remain inconclusive. Using DESI Legacy Imaging Survey data, we find that approximately 61% of barred galaxies exhibit pronounced dark gaps. We compare the location of dark gaps with resonance radii derived from the Tremaine─Weinberg method applied to MaNGA data for the same galaxies. Our analysis shows that dark gaps do not preferentially form at specific resonances. Instead, their locations correlate with  R≡RCR/RBar : slow bars tend to show shorter dark gap radii, while fast bars show longer ones. This trend reflects a tight relation between bar length and dark gap radius. However, when barred galaxies are classified by their ring morphology, certain types exhibit dark gaps that align with specific resonances. Notably, dark gaps located between the inner and outer rings are closely associated with the corotation radius. In galaxies with two dark gaps along the bar minor axis profile, the inner dark gap typically aligns with the ultraharmonic resonance, and the outer dark gap corresponds to the corotation radius. These findings suggest that some morphological types share similar  R  values and exhibit dark gaps near specific resonances. Thus, dark gaps may serve as proxies for dynamical resonances only in certain systems. Our findings may help explain the discrepancies observed in earlier studies.

Keywords: Galaxy structure, Barred spiral galaxies, Galaxy kinematics, Spiral galaxies
LATIS: Galaxy─Environment Relations at Cosmic Noon and the Role of Sample Selection. We investigate the environmental dependence of galaxy properties at z ∼ 2.5 using the Lyα Tomography IMACS Survey (LATIS), which provides high-resolution three-dimensional maps of intergalactic medium (IGM) overdensity via Lyα forest tomography. Our analysis focuses on a UV-selected spectroscopic sample of 2185 galaxies from LATIS and a complementary set of 1157 galaxies from heterogeneous spectroscopic surveys in the COSMOS field. We compare these data sets to forward-modeled mock catalogs constructed from the IllustrisTNG300-1 simulation, incorporating realistic selection functions to match both LATIS and the literature sample. While the mass-complete simulation predicts strong environmental trends—more massive and quiescent galaxies preferentially occupy overdense regions—we find that such trends are significantly weaker or absent in the observed samples. The LATIS galaxies show no measurable correlation between specific star formation rate (sSFR) and IGM overdensity, a result reproduced by LATIS-like mock catalogs, confirming that UV selection systematically excludes passive and dusty galaxies in dense environments. The literature compilation, despite improved high-mass coverage, remains incomplete and affected by similar biases. We also analyze a mass-complete photometric sample from the COSMOS-Web catalog at z ∼ 2.5 and find no detectable sSFR─environment relation, a null result that our simulations indicate can be explained by photometric redshift uncertainties. In particular, we find no evidence for a reversal of the sSFR─density relation at cosmic noon. These results demonstrate that observed correlations can be heavily shaped by selection effects and caution against inferring physical trends from incomplete spectroscopic samples. Deeper, more representative spectroscopic surveys are needed to robustly characterize environmental effects at this epoch.

Keywords: Large-scale structure of the universe, High-redshift galaxies, Galaxy evolution, Galaxy environments
A Semianalytic Framework of Population III and Subsequent Galaxy Formation on Cosmological N-body Simulations. We develop a new semianalytic framework of Population (Pop) III and subsequent galaxy formation designed to run on dark matter halo merger trees. In our framework, we consider the effect of the Lyman─Werner flux from Pop III and II stars and the dark matter baryon streaming velocity on the critical halo mass for Pop III formation. Our model incorporates the Lyman─Werner feedback in a self-consistent way; therefore, the spatial variation of Lyman─Werner feedback emerges naturally. The Pop III mass depends on the properties of a halo, which is designed to reproduce radiative hydrodynamical simulation results. We perform statistical studies of Pop III stars by applying this framework to high-resolution cosmological N-body simulations with a maximum box size of 16h−1 Mpc and enough mass resolution to resolve Pop III-forming halos. A top-heavy initial mass function emerges and two peaks corresponding to the H2 (20 ≲ z ≲ 25) and atomic cooling halos (z ≲ 15) exist in the distribution. Supermassive stars can be formed in the atomic cooling halos, and the fraction of such supermassive stars increases with the value of streaming velocity. At least an 8h−1 Mpc simulation box and the self-consistent model for the Lyman─Werner feedback are necessary to correctly model the Pop III formation in the atomic cooling halos. Our model predicts one supermassive star per halo with several 109 M⊙ at z = 7.5, which is enough to reproduce a high-redshift quasar.

Keywords: Early universe, High-redshift galaxies, Population III stars, N-body simulations
Tonalli: A Simplified 3D Multispecies Magnetohydrodynamic Model Using a Non-LTE Approximation for the Solar Chromosphere. In this work, we present the development of the Tonalli code: a simplified multispecies (H I, H II, H−, and e) magnetohydrodynamic (MHD) model in non─local thermodynamic equilibrium (NLTE) focused on solar chromospheric conditions. This new model integrates two well-established models, Newtonian CAFE (MHD) and PakalMPI (NLTE), through a self-convergence system that links the state equations used by both codes to calculate density, pressure, and temperature, with the mean molecular weight (μ) serving as a proxy. Newtonian CAFE computes the plasma variables using the ideal MHD, while PakalMPI calculates the species densities of neutral hydrogen (H I), protons (H II), negative hydrogen (H−), and electrons (ne) under the NLTE approximation. We used Tonalli to test the stability of the hydrostatic C7 model, covering 3000 km of the solar chromosphere with a vertical constant field of 30 G and a vertical constant gravity field of 274.0 ms−2. As a result, Tonalli generates 3D cubes of densities, temperature, pressure, mean molecular weight, and the departure coefficient of hydrogen in its first energy level b1, providing a detailed representation of the ionization states of the plasma at chromosphere altitudes. Despite the fact that MHD conditions can lead to numerical diffusion of the plasma, we demonstrate robustness and consistency, and self-convergence of the model with the relative error of electron density reaching values of 3.7 × 10−7.

Keywords: Solar atmosphere, Computational methods, Quiet solar chromosphere, Magnetohydrodynamical simulations
Hemispheric Asymmetry of Coronal Mass Ejections with Different Angular Widths During Solar Cycles 23─25. The angular width of coronal mass ejections (CMEs) reflects their eruption scale, dynamics, and potential geoeffectiveness. To deepen our understanding of the hemispheric distribution characteristics of CME activities, we systematically investigate the north─south asymmetry of CMEs with different angular widths. Based on the white-light CME catalog from the Coordinated Data Analysis Workshop during solar cycles 23─25, our main results are as follows: (1) the temporal evolution of CME activity across solar cycles is primarily governed by normal and partial-halo CMEs, while narrow CMEs contribute relatively little to the overall variation; (2) CME activity in cycles 23 and 25 exhibits similar hemispheric patterns, with both cycles showing southern hemisphere dominance, in contrast to the northern dominance observed in cycle 24 (this difference may be attributed to the weaker heliospheric pressure during cycle 24); (3) the phase lag between CME activities in the two hemispheres is generally within five months. These findings reveal the solar activity cycle evolution of CME angular width distributions and hemispheric asymmetries, providing new physical constraints for understanding interhemispheric coupling in solar dynamo processes and improving space weather forecasting models.

Keywords: Solar activity, Solar magnetic fields, Solar coronal mass ejections
Machine Learning Inference of Stellar Properties Using Integrated Photometric and Spectroscopic Data. Stellar astrophysics relies on diverse observational modalities—primarily photometric light curves and spectroscopic data—from which fundamental stellar properties are inferred. While machine learning (ML) has advanced analysis within individual modalities, the complementary information encoded across modalities remains largely underexploited. We present the dual embedding for stellar astronomy (DESA) model, a novel multimodal foundation model that integrates light curves and spectra to learn a unified, physically meaningful latent space for stars. DESA first trains separate modality-specific encoders using a hybrid supervised/self-supervised scheme, and then aligns them through DualFormer, a transformer-based cross-modal integration module tailored for astrophysical data. DualFormer combines cross- and self-attention, a novel dual-projection alignment loss, and a projection-space eigendecomposition that yields physically structured embeddings. We demonstrate that DESA significantly outperforms leading unimodal and self-supervised baselines across a range of tasks. In zero- and few-shot settings, DESA's learned representations recover stellar color─magnitude and Hertzsprung─Russell diagrams with high fidelity (R2 = 0.92 for photometric regressions). In full fine-tuning, DESA achieves state-of-the-art accuracy for binary star detection (AUC = 0.99, AP = 1.00) and stellar age prediction (RMSE = 0.94 Gyr). As a compelling case, DESA naturally separates synchronized binaries from young stars—two populations with nearly identical light curves—purely from their embedded positions in UMAP space, without requiring external kinematic or luminosity information. DESA thus offers a powerful new framework for multimodal, data-driven stellar population analysis, enabling both accurate prediction and novel discovery.

Keywords: Stellar astronomy, Neural networks
Converging on the Cepheid Metallicity Dependence: Implications of Nonstandard Gaia Parallax Recalibration on Distance Measures. By comparing Cepheid brightnesses with geometric distance measures including Gaia EDR3 parallaxes, most recent analyses conclude metal-rich Cepheids are brighter, quantified as γ ∼ −0.2 mag dex−1. While the value of γ has little impact on the determination of the Hubble constant in contemporary distance ladders (due to the similarity of metallicity across these ladders), γ plays a role in gauging the distances to metal-poor dwarf galaxies like the Magellanic Clouds and is of considerable interest in testing stellar models. Recently, B. F. Madore &amp; W. L. Freedman (hereafter MF25) recalibrated Gaia EDR3 parallaxes by adding to them a magnitude offset to match certain historic Cepheid parallaxes, which otherwise differ by ∼1.6σ. A calibration that adjusts Gaia parallaxes by applying a magnitude offset (i.e., a multiplicative correction in parallax) differs significantly from the Gaia Team's calibration, which is additive in parallax space—especially at distances much closer than 1 kpc or beyond 10 kpc, outside the ∼2─3 kpc range on which the MF25 calibration was based. The MF25 approach reduces γ to zero. If broadly applied, it places nearby cluster distances like the Pleiades too close compared to independent measurements, while leaving distant quasars with negative parallaxes. We conclude that the MF25 proposal for Gaia calibration and γ ∼ 0 produces farther-reaching consequences, many of which are strongly disfavored by the data.

Keywords: Cepheid variable stars, Parallax, Metallicity, Distance measure
Stellar Stripping and Disruption in Disks around Supermassive Black Hole Binaries: Repeating Nuclear Transients Prior to LISA Events. If supermassive black hole binaries (SMBHBs) are driven together by gas disks in galactic nuclei, then a surrounding nuclear star cluster or in situ star formation should deliver stars to the disk plane. Migration through the circumbinary disk will quickly bring stars to the edge of a low-density cavity cleared by the binary, where the stellar orbit becomes trapped and locked with the binary decay. Here we explore the scenario where the trapped stellar orbit decays with the binary until the binary tidally strips the star in a runaway process. For Sun-like stars, this occurs preferentially for 104─106M⊙ SMBHBs, as the SMBHB enters the LISA band. We estimate that the runaway stripping process will generate Eddington-level X-ray flares repeating on hours-to-days timescales and lasting for decades. The flaring timescales and energetics of these circumbinary disk tidal disruption events (CBD-TDEs) match well with the recently discovered quasiperiodic eruptions. However, the inferred rates of the two phenomena are in tension, unless low-mass SMBHB mergers are more common than expected. For less-dense stars, stripping begins earlier in the SMBHB inspiral, has longer repetition times, lasts longer, is dimmer, and can occur for more-massive SMBHBs. Whether CBD-TDEs are a known or a yet-undiscovered class of repeating nuclear transients, they could provide a new probe of the elusive SMBH mergers in low mass/dwarf galaxies, which lie in the sweet-spot of the LISA sensitivity.

Keywords: Gravitational wave astronomy, Supermassive black holes, Tidal disruption, Astrophysical fluid dynamics
The Balmer Break and Optical Continuum of Little Red Dots from Super-Eddington Accretion. The physical origin of little red dots (LRDs)—compact extragalactic sources with red rest-optical continua and broad Balmer lines—remains elusive. The redness of LRDs is likely intrinsic, suggesting optically thick gas emitting at a characteristic effective temperature of ∼5000 K. Meanwhile, many LRD spectra exhibit a Balmer break, often attributed to absorption by a dense gas shell surrounding an active galactic nucleus. Using semianalytical atmosphere models and radiation transport calculations, we show that a super-Eddington accretion system can give rise to a Balmer break and a red optical color simultaneously, without invoking external gas absorption for the break or dust reddening. The break originates from a discontinuity in opacity across the Balmer limit, similar to that of early-type stars, but the lower photosphere density of super-Eddington systems, ρ &lt; 10−9 g cm−3, implies a significant opacity contrast even at a cool photosphere temperature of ∼5000 K. Furthermore, while accretion in the form of a standard thin disk requires fine tuning to match the optical color of LRDs, an alternative scenario of a geometrically thick, roughly spherical accretion flow implies an effective temperature of 4000 K ≲ Teff ≲ 6000 K that is very insensitive to the accretion rate (analogous to the Hayashi line in stellar models). The continuum spectra from the latter scenario align with the Balmer break and optical color of currently known LRDs. We discuss the predictions of our model and the prospects for more realistic spectra based on super-Eddington accretion simulations.

Keywords: Accretion, Active galactic nuclei, Radiative transfer
On the Fe XXII Emission in the X-Ray Spectrum of NGC 1068. The Fe XXII doublet has been previously used to determine the density of collisionally ionized emission from magnetic cataclysmic variable stars. We test how this diagnostic doublet behaves for a photoionized plasma with the spectral energy distribution (SED) of an active galactic nucleus (AGN). We use the photoionized plasma code PION and ∼440 ks of archival Chandra High Energy Transmission Grating observations for the well-known Seyfert 2 galaxy NGC 1068 to test the behaviour of the Fe XXII doublet in the context of an AGN. This marks the first time these data have been examined with PION. We find that in a photoionized plasma, the Fe XXII doublet is dependent on the density, ionization state, and SED used. Thus, this density diagnostic remains model-dependent. In the context of NGC 1068 the doublet predicts an emission region ∼100rg from the central black hole. This would require a direct line of sight to the central engine, which is at odds with the Seyfert 2 nature of this source. In practice, these results highlight the complexities and challenges of applying photoionized models. With these data, we cannot exclude the possibility of a direct line of sight to the central engine of NGC 1068, but we cannot confirm it. Future observations with instruments such as Athena are needed to explore the Fe XXII doublet further.

Keywords: X-ray astronomy, Atomic spectroscopy, Seyfert galaxies, X-ray active galactic nuclei
Toward a General Theory of Grain Alignment and Disruption by Radiative Torques and Magnetic Relaxation. We generalize the magnetically enhanced radiative torque (MRAT) theory for astrophysical environments described by a dimensionless parameter U/(n1T2) with U the radiation strength, n1 = nH/(10 cm−3) the normalized hydrogen density, and T2 = Tgas/100 K the normalized gas temperature. We derive the critical magnetic relaxation δmag,cri required to produce high-J attractors for different radiative torque (RAT) models and local conditions, and find that δmag,cri must increase with increasing U/(n1T2). We numerically study grain alignment and rotational disruption by the MRAT mechanism, considering both gas collisions and magnetic fluctuations. We find that, for the collision-dominated regime (U/(n1T2) ≤ 1), collisional and magnetic excitations slowly transport large grains from low-J to high-J attractors, leading to perfect slow alignment within ∼10─100 damping times due to MRAT. However, for the radiation-dominated regime (U/(n1T2) &gt; 1), only a fraction of grains can be fast aligned at high-J attractors by MRAT, and the majority of grains are trapped at low-J rotation due to strong RATs, a new effect termed RAT trapping. For extreme conditions of U/(n1T2) &gt; 104, the efficiency of magnetic relaxation on grain alignment is suppressed, and grains only have fast alignment and disruption purely determined by RATs. We quantified the fraction of grains with fast alignment at high-J attractors,  fhigh−Jfast , for different RAT models, magnetic relaxation, and U/(n1T2), and found that the maximum  fhigh−Jfast  can reach 45% by MRATs and 22% by RATs. We discuss the implications of our results for describing alignment and disruption of astrophysical dust.

Keywords: Dust physics, Dust destruction, Circumstellar dust, Astrophysical dust processes, Starlight polarization, Interplanetary dust, Polarimetry
Fractal Aggregate Aerosols in the Virga Cloud Code. I. Model Description and Application to a Benchmark Cloudy Exoplanet. We introduce new functionality to treat fractal aggregate aerosol particles within the Virga cloud modeling framework. Previously, the open-source cloud modeling code Virga, the Python version of EddySed, assumed spherical particles to compute particle mass and size distributions throughout the atmosphere. The initial release of Virga also assumed spherical particles to compute Mie scattering properties, which include the single scattering albedo, asymmetry parameter, and optical depth as a function of particle radius and composition. However, extensive evidence from solar system aerosols, astrophysical disks and dust, and Earth climate studies suggests that nonspherical aggregate particles are common compared to idealized compact spherical particles. Following recent advances in microphysical and opacity modeling, we implement a simple parameterization for dynamical and optical (modified mean field theory) effects of fractal aggregate particles into Virga. We then use this new functionality to perform a case study using basic planetary parameters similar to the well-characterized, aerosol-laden mini-Neptune GJ 1214 b, using KCl clouds made of aggregate particles. We choose KCl to most directly explore comparisons to previous studies. We demonstrate (1) how our method compares to previous fractal aggregate particle treatments and (2) how our new fractal treatment affects theoretical spectra of cloudy atmospheres. Overall, our model is faster and more flexible for a wider range of parameter space than previous studies. We explore the limitations of our modeling setup and offer guidance for future investigations using our framework.

Keywords: Brown dwarfs, Theoretical models, Infrared spectroscopy, Atmospheric clouds, Transmission spectroscopy, Atmospheric dynamics, Exoplanet atmospheres
ML-driven Strong Lens Discoveries: Down to θ<SUB>E</SUB><inline-formula> <mml:math><mml:mspace></mml:mspace><mml:mo>∼</mml:mo><mml:mspace></mml:mspace><mml:mn>0</mml:mn><mml:mover><mml:mrow><mml:mo>.</mml:mo></mml:mrow><mml:mrow><mml:mtext>″</mml:mtext></mml:mrow></mml:mover><mml:mn>03</mml:mn></mml:math> </inline-formula> and M<SUB>halo</SUB> &lt; 10<SUP>11</SUP>M<SUB>⊙</SUB>. We present results on extending the strong lens discovery space down to much smaller Einstein radii ( θE≲0.″03 ) and much lower halo mass (Mhalo &lt; 1011M⊙) through the combination of JWST observations and machine learning (ML) techniques. First, we forecast detectable strong lenses with JWST using CosmoDC2 as the lens catalog, and a source catalog down to 29th magnitude. By further incorporating the VELA hydrodynamical simulations of high-redshift galaxies, we simulate strong lenses. We train a ResNet on these images, achieving near-100% completeness and purity for "conventional" strong lenses ( θE≳0.″5 ), applicable to JWST, the Hubble Space Telescope (HST), the Roman Space Telescope, and Euclid VIS. For the first time, we also search for very low halo mass strong lenses (Mhalo &lt; 1011M⊙) in simulations, with  θE≪0.″5 , down to the best resolution ( 0.″03 ) and depth (10,000 s) limits of JWST using ResNet. A U-Net model is employed to pinpoint these small lenses in images, which are otherwise virtually impossible for human detection. Our results indicate that JWST can find ∼17/deg2 such low-halo-mass lenses, with the locations of ∼1.1/deg2 of these detectable by the U-Net at ∼100% precision (and ∼7.0/deg2 at a 99.0% precision). To validate our model for finding "conventional" strong lenses, we apply it to HST images, discovering two new strong lens candidates previously missed by human classifiers in a crowdsourcing project (E. O. Garvin et al. 2022). This study demonstrates the (potentially "superhuman") advantages of ML combined with current and future space telescopes for detecting conventional, and especially, low-halo-mass strong lenses, which are critical for testing cold dark matter models.

Keywords: Strong gravitational lensing, Dwarf galaxies, Cold dark matter, Gravitational lensing, Dark matter