Sazuna/UAT_keywords huggingface dataset:
Limitations on Morphological Fitting for JWST "Little Red Dots". Early results from JWST have uncovered a peculiar class of objects referred to as "little red dots" (LRDs). The extremely compact morphologies of these LRDs are often invoked to point towards an active galactic nucleus (AGN)-dominated picture in the context of their conflicting multiwavelength properties. In this work, we assess the capability of pysersic and GALFIT—commonly used tools in LRD morphological studies—to recover input parameters for a simulated suite of LRD-like objects in the F444W band. We find that (1) these tools have difficulty recovering input parameters for simulated images with signal-to-noise ratio (SNR) ≲ 25; (2) estimated point-spread function (PSF) fraction could be a more robust physically motivated description of LRD compactness; and (3) almost all permutations of modeled LRDs with SNR ≲ 50 cannot be differentiated from a point source, regardless of intrinsic extent. This has serious implications on how we interpret morphological results for increasingly large photometric samples of LRDs, especially at extremely high z or in relatively shallow fields. We present results of Sérsic and two-component fitting to a sample of observed LRDs to compare with our mock sample fitting. We find that ∼85% of observed LRDs are PSF dominated, consistent with the AGN-dominated interpretation. The remaining ∼15% have low estimated PSF fractions (two-component fit) and sizes ≳150 pc (Sérsic fit). This morphological diversity of LRDs suggests that that the population likely is not homogeneous. It possibly has a primary subset of LRDs consistent with the AGN-dominated hypothesis, and a secondary population more consistent with arising perhaps from extremely compact starbursts.

Keywords: AGN host galaxies, Starburst galaxies, Active galaxies, Active galactic nuclei, High-redshift galaxies
A Multilayer Magnetohydrodynamic Shallow-water Model of The Solar Tachocline: Equilibrium Shape and Thickness. We build a multilayer magnetohydrodynamic shallow-water model to study the thickness and shape of the solar tachocline. This allows us to include characteristics of both the overshoot and the radiative parts of the tachocline. The equations derived include equilibrium in latitude among Coriolis, pressure gradient, and magnetic curvature stresses for each layer, and magnetohydrostatic equilibrium in the radial direction. In each layer, the total mass is conserved; mass is redistributed for different amplitudes and latitude positions of toroidal bands, thus producing variations in tachocline shape and thickness with solar cycle phases. While we solve here for equilibrium of two layers, the equations can be readily generalized for additional layers. In pure hydrodynamic tachocline with no differential rotation, thickness and shape are independent of latitude. With differential rotation and/or magnetic fields, the tachocline is, in general, oblate in equatorial regions but prolate in polar latitudes. A local bump occurs at the poleward side of tachocline toroidal band. Hence, depending on latitude-location and amplitude of magnetic band as function of solar cycle, the local bump drifts equatorward trailing the magnetic field. Oblateness and prolateness are much larger in the overshoot than in the radiative layer, due to its lower effective gravity. Our results can provide guidance for interpreting helioseismic estimates of variations in tachocline shape and thickness in latitude, including upper limits to banded toroidal field amplitudes.

Keywords: Magnetohydrodynamics, Solar differential rotation, The Sun, Solar magnetic fields, Solar activity
Probing Active Galactic Nuclei─Interstellar Medium Feedback through Extended X-Ray Emission in ESO 137-G034. We present a detailed analysis of the X-ray emission of the Compton-thick (CT) active galactic nuclei (AGN) ESO 137-G034 based on deep (∼230 ks) Chandra observations. As in other CT AGNs, the morphology of the emission is elongated, approximately following the [O III] ionization bicone. With spatially resolved spectral modeling, we show that the extended emission within the bicone regions is most readily explained as from a mixture of photoionized gas and shock-heated plasma, reflecting the combined effects of radiative and kinematic AGN feedback. By comparing the morphology of the X-ray emission in narrow spectral bands and that of the 3 cm radio jet, we find suggestive evidence of thermal, possibly shocked emission associated with the SE termination of the radio jet. This interpretation is also supported by the lack of [O III] relative to the 0.3−3.0 keV flux in the inner 3″ (∼600 pc) of the SE cone, which would be consistent with an additional thermal X-ray component on top of the photoionized emission of an outflowing wind. A similar effect is only seen within the inner 1″ (200 pc) of the NW cone. In the radial profile of the [O III]/X-ray flux ratio and the X-ray hardness ratio within the inner ∼3″ (∼600 pc) of the SE cone, we see an asymmetry, with no counterpart in the NW cone. We detect soft extended X-ray emission in the cross cones, which may originate from the interaction of an embedded radio jet with a clumpy interstellar medium. These results highlight the importance of both radiative and mechanical feedback in shaping the circumnuclear environment of ESO 137-G034.

Keywords: AGN host galaxies, High energy astrophysics, Diffuse radiation, X-ray active galactic nuclei, Active galactic nuclei, Interstellar medium, Shocks
Mapping the Orbital Landscape of Perturbing Planet Solutions for Single-planet Systems with TTVs. There are now thousands of single-planet systems observed to exhibit transit timing variations (TTVs), yet we largely lack any interpretation of the implied masses responsible for these perturbations. Even when assuming these TTVs are driven by perturbing planets, the solution space is notoriously multimodal with respect to the perturber's orbital period, and there exists no standardized procedure to pinpoint these modes besides blind brute-force numerical efforts. Using N-body simulations with TTVFast and focusing on the dominant periodic signal in the TTVs, we chart out the landscape of these modes and provide analytic predictions for their locations and widths, providing the community with a map for the first time: the TTV circus tent diagram. We then introduce an approach for modeling single-planet TTVs in the low-eccentricity regime by splitting the orbital period space into a number of uniform prior bins over which there are none of these degeneracies. We show how one can define appropriate orbital period priors for the perturbing planet in order to sufficiently sample the complete parameter space. We demonstrate, analytically, how one can explain the numerical simulations using first-order near mean-motion resonance superperiods, the synodic period, and their aliases—the expected dominant TTV periods in the low-eccentricity regime. Using a Bayesian framework, we then present a method for determining the optimal solution between TTVs induced by a perturbing planet and TTVs induced by a moon.

Keywords: Transits, Model selection, Exoplanet systems, Astrostatistics, Exoplanet astronomy, Transit timing variation method
Whistler─Alfvén Turbulence in a Nonneutral Ultrarelativistic Pair Plasma. The large-scale dynamics of most conventional space and astrophysical plasmas are predominantly governed by Alfvén modes, which are low-frequency magnetohydrodynamic modes existing in magnetized media. At scales smaller than the ion gyroscale or frequencies exceeding the ion cyclotron frequency, the Alfvén modes transform into kinetic-Alfvén or whistler modes that significantly contribute to plasma dynamics. However, this scenario reverses in nonneutral pair plasmas, such as those found in the magnetospheres of pulsars and magnetars, around rotating black holes, and in their relativistic jets, as well as in certain laboratory plasmas. In these systems, the large-scale dynamics are governed by hybrid whistler─Alfvén modes, which transform into pure Alfvén modes at smaller scales. We derive the nonlinear equations that describe the dynamics of whistler─Alfvén modes in ultrarelativistic nonneutral magnetically dominated pair plasma and discuss the spectrum of turbulence governed by these equations.

Keywords: Plasma astrophysics
Shadows of the Colossus: Hierarchical Black Hole Mergers in a 10-million-body Globular Cluster Simulation. The LIGO/Virgo/Kagra (LVK) Collaboration has detected numerous binary black hole (BBH) mergers with properties that challenge standard binary evolution scenarios, such as component masses above the pair-instability gap and high spin magnitudes. Dense stellar environments such as globular clusters provide a natural channel for producing such systems through hierarchical mergers, where black hole (BH) remnants formed in earlier mergers are retained in the cluster and undergo successive mergers. However, gravitational-wave recoil kicks often eject merger remnants from typical globular clusters, which limits hierarchical growth. Massive clusters with deeper potential wells, such as those found in giant elliptical galaxies like M87, may overcome this barrier, but direct simulations of such massive globular clusters remain computationally challenging. In this study, we present a 10-million-body cluster simulation performed with the Cluster Monte Carlo (CMC) code, referred to as colossus, which serves as a proxy for the most massive low-metallicity globular clusters observed in the local Universe. This simulation demonstrates that extended chains of hierarchical mergers can occur in massive globular clusters, producing BHs up to the fifth generation with masses approaching 250 M⊙, comparable to the most massive LVK events observed to date (e.g., GW231123). Combining the colossus simulation with the previous CMC Cluster Catalog, we develop a framework to extrapolate BBH merger predictions for the thousands of globular clusters seen in the Virgo Supercluster.

Keywords: Globular star clusters, Intermediate-mass black holes, Stellar mass black holes, Gravitational waves, N-body simulations
A Systematic NLTE Study of Very Metal-poor Stars with Metallicity down to −4.3 dex. VI. Light Neutron-capture Elements and the Sr─Na Correlation as a Signature of Spinstar Nucleosynthesis in the Early Galaxy. We present a non─local thermodynamic equilibrium (NLTE) abundance analysis of the light neutron-capture elements Sr, Y, and Zr in a sample of 103 very metal-poor stars spanning −4.3 ≲ [Fe/H] ≲ −1.7, based on high-resolution Subaru/HDS spectra and atmospheric parameters from Paper I. This is the first NLTE study of Sr−Y−Zr abundances using a large, homogeneous sample optimized for tracing Galactic chemical evolution (GCE). We find a mild positive trend in [Sr, Y, Zr/Fe] with [Fe/H], consistent with GCE models that incorporate s-process, electron-capture supernovae, compact object mergers, and magnetorotational supernovae, without invoking additional light-element primary processes. We report a statistically significant correlation between [Sr/Fe] and [Na/Fe] in our stellar sample. This finding supports the contribution of fast-rotating massive stars (spinstars) to the simultaneous production of sodium through hydrogen burning and light neutron-capture elements via the weak s-process in low-metallicity environments. We identify five Sr-poor stars exhibiting significantly lower Sr, Y, and Zr abundances than other stars at similar [Fe/H], pointing to chemical inhomogeneities in early star-forming environments. These light neutron-capture elements therefore provide valuable tracers of early nucleosynthetic processes and the Milky Way's assembly history.

Keywords: Stellar abundances, Stellar nucleosynthesis, Chemical abundances, Galaxy chemical evolution
Thermal Baroclinic Instabilities in Accretion Disks. I. Combined Dispersion Relation for Goldreich─Schubert─Fricke Instability and Convective Overstability in Disks around Young Stars. This paper discusses the Goldreich─Schubert─Fricke instability (GSF) and the convective overstability (COS) in the context of baroclinic thermal instabilities in rotating disks around young stars. The vertical shear instability (VSI) is a global extension of the GSF that affects geometrically thin disks but follows the same stability criterion. The COS also possesses a twin for stellar interiors, specifically, Shibahashi's vibrational stability of rotating stars. We derive a combined dispersion relation for GSF and COS with arbitrary cooling times for local perturbations and determine a new stability criterion beyond the Solberg─Høiland criterion. The paper shows that in extension to the COS stability criterion for the vertically unstratified case ( NR2&gt;0 ), one additionally needs a barotropic disk structure to ensure stability. We demonstrate that a baroclinic disk atmosphere always has a buoyantly unstable direction, although not necessarily in the radial direction. The paper predicts that for cooling times longer than the critical cooling time for VSI, GSF modes will always be accompanied by COS modes of similar growth rate. The numerical companion paper II tests the predictions of growth rates from this paper.

Keywords: Stellar accretion disks, Stellar rotation, Astrophysical fluid dynamics, Hydrodynamics
Potential Nitrogen Enrichment via Direct-collapse Wolf─Rayet Stars in a z = 4.7 Star-forming Galaxy. We present analyses of a nitrogen-enriched star-forming galaxy, ID60001, at z = 4.6928 based on James Webb Space Telescope/NIRSpec Multi-Object Spectroscopy and NIRCam photometry. From rest-frame optical emission lines we derive the nitrogen-to-oxygen (N/O) abundance ratio of ID60001 to be  log(N/O)=−0.76−0.03+0.03  ( [N/O]=0.10−0.03+0.03 ), which is significantly elevated at the corresponding metallicity  12+log(O/H)=7.75−0.01+0.01  (Z/Z⊙ = 0.12) compared to local counterparts. We discuss possible scenarios for elevated N/O abundance in ID60001, including pristine gas inflow, Wolf─Rayet (W-R) stars, and oxygen depletion by Type II supernova winds. Based on the moderately broadened He IIλ4686 emission line, galaxy morphology, and star formation history, we conclude that the elevated N/O abundance of ID60001 is likely originated from massive (&gt;25 M⊙) W-R stars that directly collapse into a black hole. We also stress the importance of reliable electron density measurements when deriving N/O abundance with rest-frame optical emission lines.

Keywords: Interstellar medium, Galaxy evolution, Chemical abundances
Star Formation Histories and Gas Content Limits of Three Ultra-faint Dwarfs on the Periphery of M31. We present Hubble Space Telescope (HST) imaging of Pegasus V and Pisces VII, along with a re-analysis of the archival imaging of Pegasus W, and Karl Jansky Very Large Array (VLA) neutral gas (H I) observations of all three. These three ultra-faint dwarfs (UFDs) are all within the Local Group in the approximate direction of M31. The VLA observations place stringent upper limits on their H I content, with all having MHI &lt; 104 M⊙. As the red giant branches of these UFDs are sparsely populated, we determined distances from the HST photometry of horizontal branch (HB) stars in comparison to a fiducial HB population (from M92), with all three falling in the range 0.7─1 Mpc. Using a new Python-based star formation history (SFH) fitting code (based on StarFISH), we derive SFHs of all three UFDs. As found previously, the best-fit SFH for Pegasus W includes significant star formation well beyond the end of reionization, while the SFHs calculated for Pegasus V and Pisces VII are consistent with them having quenched over 10 Gyr ago. These findings for the latter two objects indicate that, like those in the vicinity of the Milky Way, lower-mass UFDs in the vicinity of M31 likely quenched at early times.

Keywords: Local Group, Galaxy distances, Interstellar atomic gas, Dwarf galaxies, Galaxy stellar content
Modified Cosmology or Modified Galaxy Astrophysics is Driving the z &gt; 6 JWST Results? Cosmic Microwave Background Experiments Can Discover the Origin in the Near Future. The massive and bright galaxies observed by the James Webb Space Telescope (JWST) at high redshifts (z &gt; 6) have challenged our understanding of the Universe. This may require revisiting the physics of galaxy formation and evolution, or modifying the ΛCDM cosmological model to explain these observations, or both. We show that high-resolution cosmic microwave background (CMB) experiments such as the Simons Observatory (or CMB-S4) can measure smoking-gun signatures jointly in weak lensing and kinematic Sunyaev─Zeldovich (kSZ) power spectra, which can shed light on both these scenarios. An increase in the matter power spectrum at small scales will enhance the number density of dark matter halos at high redshifts, thereby increasing the galaxy formation rate. This will cause enhanced weak lensing signal from these redshifts and also lead to an enhanced patchy-kSZ signal from the Epoch of Reionization. However, if only galaxy astrophysics is modified, without any modification in the matter power spectrum, then the patchy-kSZ signal gets altered, while the weak lensing signal remains nearly unaltered. We show that we can measure the modified astrophysical and cosmological scenarios at a statistical significance of 10.4σ (and 29.8σ) from the Simons Observatory (and CMB-S4), which will enable a conclusive understanding on what physical process is driving the high-redshift observations of JWST.

Keywords: Weak gravitational lensing, Cosmic microwave background radiation, Sunyaev-Zeldovich effect, Reionization, High-redshift galaxies
Scalable and Robust Multiband Modeling of AGN Light Curves in Rubin-LSST. The Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) will monitor tens of millions of active galactic nuclei (AGNs) for a period of 10 yr with an average cadence of 3 days in six broad photometric bands. This unprecedented data set will enable robust characterizations of AGN UV/optical variability across a wide range of AGN physical properties. However, existing tools for modeling AGN light curves are not yet capable of fully leveraging the volume, cadence, and multiband nature of LSST data. We present EzTaoX, a scalable light-curve modeling tool designed to take advantage of LSST's multiband observations to simultaneously characterize AGN UV/optical stochastic variability and measure interband time delays. EzTaoX achieves a speed increase of ∼102─104× on CPUs over current tools with similar capabilities, while maintaining equal or better accuracy in recovering simulated variability properties. This performance gain enables continuum time-delay measurements for all AGNs discovered by LSST—both in the Wide Fast Deep survey and the Deep Drilling Fields—thereby opening new opportunities to probe AGN accretion-flow geometries. In addition, EzTaoX's multiband capability allows for robust characterization of AGN stochastic variability down to hourly timescales, facilitating the identification of accreting low-mass AGNs—such as those residing in dwarf galaxies—through their distinctive variability signatures.

Keywords: Astronomy software, Reverberation mapping, Active galactic nuclei, Gaussian Processes regression, Red noise, Time series analysis
Limb Shift of the Fe I 6569 Å Line on the Sun. The convective motions of solar granules generate a center-to-limb variation of Doppler velocity in the photospheric lines, known as the limb shift effect. This study presents a comprehensive analysis of this effect for the Fe I 6569 Å line using both observational data from the Chinese Hα Solar Explorer (CHASE) mission and numerical simulations from the Bifrost code. We employ two independent methods to derive the limb shift curve: a spectral-averaging method (Method 1) and a velocity-averaging method (Method 2). By comparing synthetic and observed data, we determine the convective blueshift, which is not accounted for in the CHASE observations. The simulations reproduce the observed trends for both methods at the instrument's spatial resolution (=1 .″ 2). However, at resolutions below &lt;1″, Method 2 produces limb-shift curves that depart significantly from both Method 1 results and traditional limb-shift profiles, whereas Method 1 remains in agreement with classical behavior. Further analysis finds that the results from Method 1 comprise two distinct components: a contrast contribution caused by the correlation between velocity and line depth and a Dopplergram contribution caused by density inhomogeneities and corrugation effects.

Keywords: Solar granules, Center to limb observations, Radiative transfer
Temporal Variations in Pulsar Spectropolarimetry: Findings from Millisecond Pulsar J2144─5237 Using Parkes UWL Receiver. While the temporal variations of the spectropolarimetric nature of pulsars remain unexplored, this investigation offers significant potential for uncovering key insights into pulsar emission mechanisms, magnetic field geometry, and propagation effects within the magnetosphere. We developed a package for investigating time-varying spectral behavior for full Stokes parameters and demonstrate it on a millisecond pulsar (MSP), J2144−5237, in a binary system (orbital period ∼10 days) using the Parkes Ultra-Wideband Low receiver. In this study we report rotation measure variation with orbital phase. We find that the temporal variations in the spectra of Stokes I, Q, and V are generally correlated throughout the orbit, while Stokes U exhibits intervals of both correlation and anticorrelation with Stokes I, depending on the orbital phase. We also provide a Poincaré sphere representation of the polarization properties of J2144−5237, demonstrating a systematic temporal change of Poincaré sphere location for the main component with orbital phase. To our knowledge, this is the first investigation of the time-varying properties of the spectropolarimetric nature of any pulsars or MSPs. Extending this study to probe the spectrotemporal nature of full Stokes data on a larger sample of MSPs or pulsars has the potential to provide vital information on emission mechanisms inside the magnetosphere, interstellar propagation effects, and binary interactions.

Keywords: Radio pulsars, Spectropolarimetry, Binary pulsars, Millisecond pulsars
On the Deepest Search for Galactic Center Pulsars and an Examination of an Intriguing Millisecond Pulsar Candidate. We report the results of one of the most sensitive pulsar surveys to date targeting the innermost region of the Galactic center (GC) using the Robert C. Byrd Green Bank Telescope at X band (8─12 GHz) using data from the Breakthrough Listen initiative. In total, we collected 9.5 hr of data covering the wider  ∼8' diameter of the GC bulge, and 11 hr on the inner 1 .' 4 region between 2021 May and 2023 December. We conducted a comprehensive Fourier-domain periodicity search targeting both canonical pulsars (CPs) and millisecond pulsars (MSPs), using constant and linearly changing acceleration searches to improve sensitivity to compact binaries. Assuming weak scattering, our searches reached luminosity limits of  Lmin≍0.14mJykpc2  for CPs and  Lmin≍0.26mJykpc2  for MSPs—sensitive enough to detect the most luminous pulsars expected in the GC. Among 5282 signal candidates, we identify an interesting 8.19 ms MSP candidate (dispersion measure (DM) of 2775 pc cm−3), persistent in time and frequency across a 1 hr scan at a flux density of  Smin≍0.007mJy . We introduce a novel randomization test for evaluating candidate significance against noise fluctuations, including signal persistence via Kolmogorov─Smirnov tests and flux-versus-DM behavior. We are unable to make a definitive claim about the candidate due to a mixed degree of confidence from these tests and, more broadly, its nondetection in subsequent observations. This deepens the ongoing missing pulsar problem in the GC, reinforcing the idea that strong scattering and/or extreme orbital dynamics may obscure pulsar signals in this region.

Keywords: Neutron stars, Black hole physics, Galactic center, Millisecond pulsars, Surveys, Pulsars, Radio telescopes, Radio transient sources, Magnetars, Binary pulsars, Radio pulsars