Sazuna/UAT_keywords huggingface dataset:
Considering Contact Forces during the Formation of Planetesimals by Gravitational Collapse: Mutual Orbits, Spin States, and Shapes. In this work, we apply a soft-sphere discrete element method (SSDEM) within the PKDGRAV N-body integrator to investigate the formation of planetesimal systems through the gravitational collapse of clouds of superparticles. Previously published numerical models have demonstrated that the gravitational collapse of pebble clouds is an efficient pathway to produce binary planetesimal systems. However, such investigations were limited by their use of a perfect-merger and inflated-radii superparticle approach, which inhibits any analysis of planetesimal shapes and spin states, precludes the formation of the tightest binary orbits, and produces significantly underdense planetesimals. The SSDEM enables superparticles to rest upon each other through mutual surface penetration and by simulating contact physics. Superparticles do not need to be inflated, and collisions are not treated as perfect mergers; we can thus track the evolution of planetesimal shapes, spins, and tight binary orbits. We demonstrate that the SSDEM is an excellent method to model the collapse process, and is capable of producing many binary planetesimal systems from a single cloud. The most massive systems often exhibit low-inclination (i ≲ 15°) and moderately eccentric (e ≲ 0.40) orbits within a tight range of semimajor axes normalized by their Hill radii (a/RHill ∼ 0.02–0.15). Conversely, less massive planetesimal systems display a wider range of eccentricities and inclinations and maintain a wider range of a/RHill (0.15 to ≥0.50). These results confirm the findings of previously published perfect-merging models while also producing novel results about planetesimal spin and shape properties. Newly formed planetesimals exhibit 10 hr rotation periods on average and can be characterized by a wide variety of shapes (spherical, oblate, top-shaped, flattened, egg-shaped, or prolate), with the most massive planetesimals primarily forming as spheres and oblate spheroids.

Keywords: Kuiper belt, Classical Kuiper belt objects, Natural satellite formation, Asteroid satellites, Main belt asteroids, Asteroid rotation, Trans-Neptunian objects, Asteroid belt, Planet formation, Planetesimals
Formation of a Nuclear Star Cluster through a Merger Event in the Low-surface-brightness Galaxy AGC 223218. We present the properties of a nuclear star cluster (NSC) in the low-surface-brightness galaxy AGC 223218. The disk of the galaxy can be modeled using two Sérsic components with distinct central positions: one representing the inner bright disk and the other corresponding to the extended outer disk. We estimate the stellar masses of the NSC and the host galaxy using two methods: spectral energy distribution (SED) fitting and mass-to-light versus color relations (MLCRs). The stellar mass ratio of the NSC to AGC 223218 is 0.094 based on the SED method and 0.072 using MLCRs. The NSC presents a younger stellar population and a lower [Fe/H] value than the host, as determined from Sloan Digital Sky Survey (SDSS) and LAMOST spectra analysis using pPXF fitting. AGC 223218 is located at the boundary between the Seyfert and star-forming regions in the [S II]-Baldwin–Phillips–Terlevich (BPT) diagram, whereas in the [N II]-BPT diagram, it falls in the track of star-forming SDSS galaxies. This suggests the presence of strong shocks in AGC 223218. We propose that the NSC in AGC 223218 may have formed as a result of a merger event. Furthermore, the observed X-ray luminosity of AGC 223218 with eROSITA is 2 orders of magnitude higher than the expected X-ray luminosity from X-ray binaries, suggesting the presence of an intermediate-mass black hole (IMBH) in the NSC. To account for the observed X-ray luminosity, we estimate the IMBH accretion rate to be approximately 0.001.

Keywords: Star clusters, Galaxy evolution, Low surface brightness galaxies
r-process Abundance Dispersion in the Globular Cluster M5 Using Keck Archival Data. We studied 28 red giant branch stars in the mildly metal-rich globular cluster M5 ([Fe/H] = −1.29) using archival high-resolution spectra from the Keck Observatory archive to better understand the r-process in globular clusters. Previous studies (M15, M92, and NGC 2298) have shown r-process dispersion in varying amounts, hinting at the source of the r-process in those clusters. We extend these dispersion studies to the more metal-rich cluster M5 by studying the rare-earth peak, specifically the elements Ba, Nd, and Eu. We separately analyze the different stellar generations, as traced by the abundance of Na and O. Based on the Nd and Eu abundances, we report a tenuous detection of r-process dispersion that is dependent on the generation and element. Based on a log-likelihood dispersion study accounting for measurement errors, Nd has an intrinsic first-generation abundance spread of  σ1G(Nd)=0.15−0.07+0.10  and a 2σ upper limit on the second-generation spread of σ2G(Nd) &lt; 0.28. The upper limits on the Eu intrinsic spread are σ1G(Eu) &lt; 0.34 and σ2G(Eu) &lt; 0.16. A potential dispersion implies the cluster gas was inhomogeneously polluted, either due to an event concurrent with the formation of the cluster or due to clouds of disparate composition that coalesced to form the cluster.

Keywords: Globular star clusters, R-process, Chemical abundances, Spectroscopy
A Comparison of Full Spectral Fitting Codes for Measuring the Stellar Initial Mass Function and Other Stellar Population Properties in Elliptical Galaxies. We present a comparative test of four widely used full spectral fitting codes, with the aim of answering the question: How robust is the retrieval of the stellar initial mass function (IMF) and other stellar properties of galaxies? We used Absorption Line Fitter (ALF), Python Stellar Absorption Feature Fitting (PYSTAFF), Starlight, and Penalized PiXel-Fitting (PPXF) to fit a set of optical+near-IR spectroscopic data from the Magellan telescope of the two brightest galaxies in the Fornax cluster, NGC 1399 and NGC 1404. By fitting the same data set with the same models, we can compare the radial trends (out to ∼1 Re) of IMF slope, age, metallicity, and 19 elemental abundances when allowed with the four codes. To further test the robustness of our analysis, we carried out parallel simulations by creating inputs with different star formation history (SFH) complexity. The results from simulations show that codes such as ALF and PYSTAFF, which both assume a simple stellar population (SSP), return greater precision and accuracy only when the underlying population is a pure SSP; however, in cases where the SFH is more complex, these codes return erroneous results. Although codes like STARLIGHT and PPXF, which retrieve the best-fit SFH without prior assumptions, tend to produce results with greater scatter and bias, they are generally more reliable in identifying secondary components. Our analysis on the two targets shows that ALF and PYSTAFF, which assume an SSP, give results pointing to a single old age, a decreasing metallicity with radius, and a flat super-Salpeter IMF. In contrast, STARLIGHT and PPXF suggest the presence of a secondary component with different metallicity and IMF characteristics. *This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Keywords: Initial mass function, Early-type galaxies
Using the Hanle Effect in Mg II k to Quantify the Open Flux above the Solar Poles. We test the use of the Mg II resonant lines for measurement of the magnetic field at the top of the chromosphere of polar coronal holes (CHs). The Hanle effect in the core of Mg II k enables access to a regime of field strengths where the Zeeman effect has little diagnostic value (especially at the solar poles, where most of the field is transverse to the line of sight). Synthetic Stokes spectra computed from a radiation magnetohydrodynamic simulation of a CH emulating a high viewing angle are inverted with the HanleRT Tenerife Inversion Code, which accounts for the physical processes that lead to scattering-induced polarization and its modification due to the magnetic field and other symmetry-breaking mechanisms. We find that, while degeneracies in the atmospheric model lead to poor inferences of the thermodynamical properties, the magnetic inferences are highly consistent with the model values. The mean magnetic field strength in the simulation cube is typically retrieved with a relative error of δB ∼ 20% and an absolute error of ∆B ∼ 2 G at the top of the chromosphere. This opens up an avenue for promising chromospheric constraints for magnetic extrapolation models that ingest photospheric magnetograms, whose biases and uncertainties are troublesome to the reconstruction of the heliospheric magnetic field.

Keywords: Solar chromosphere, Spectropolarimetry, Radiative transfer
ΛCDM Star Clusters at Cosmic Dawn: Stellar Densities, Environment, and Equilibrium. The James Webb Space Telescope (JWST) has opened a window on many new puzzles in the early Universe, including a population of high-redshift star clusters with extremely high stellar surface density, suggesting unique star formation conditions in the Universe's early evolution. We study the formation and evolution of these first star clusters and galaxies using an AREPO cosmological simulation box designed to resolve the intricate environments of the smallest halos hosting Population III star clusters at z ≥ 12. Our approach, which prioritizes baryonic structure identification through a friends-of-friends algorithm, provides new insights into early star cluster formation and delivers predictions directly relevant to observations. We investigate the dynamical properties of these first star clusters and use numerical and analytical methods to understand the populations of virialized and nonvirialized systems. Our findings indicate that high-z star clusters in a feedback-free regime can achieve extreme surface densities, consistent with the systems detected by JWST. These results imply that JWST may have the opportunity to uncover stellar systems at high redshift whose dynamical state preserves evidence of the hierarchical structure formation process.

Keywords: Hydrodynamical simulations, Population III stars, James Webb Space Telescope, High-redshift galaxies, Star clusters
High-resolution Optical IFU Spectroscopy of the Complex Galaxy Merger II Zw 096. Luminous and ultraluminous IR galaxies are critical for investigating feedback mechanisms due to a combination of intense star formation episodes and active galactic nuclei (AGN), particularly in the context of complex galaxy interactions. We conduct a detailed analysis of the II ZW 096 merging system using the Multi-Unit Spectroscopic Explorer on the Very Large Telescope, combining high-resolution narrow-field mode and large-area wide-field mode observations. We mapped the morphology, kinematics, and ionizing radiation of the system's gas by fitting atomic emission lines and the optical continuum. We identify three or more distinct galaxies within II ZW 096, revealing rotational patterns and complex interactions consistent with a collapsing small galaxy group. The kinematics and ionization structures suggest high star formation rates and shock-driven processes, which align with this proposed scenario. Focusing on the D1 compact region, which contributes 40%─70% of the system's IR emission, and combining information from archival multiwavelength observations, we find strong evidence of a heavily obscured AGN powering it. Our analysis of the internal structure, interactions, and merger state of II ZW 096 offers novel insights into the galaxy evolution processes in this dynamic and highly chaotic system.

Keywords: Supermassive black holes, Galaxy interactions, Infrared galaxies, Spectroscopy
The Multiple Paths to Merger of Unequal-mass Black Hole Binaries in the Disks of Active Galactic Nuclei. The accretion disks that power active galactic nuclei (AGN) are thought to house populations of stars and compact objects; after forming binaries these compact objects may merge, begetting gravitational waves (GWs) such as those detected by LIGO and VIRGO. We present a comprehensive study of the early evolution of binaries within AGN disks as their orbits are influenced by the surrounding gas, focusing on eccentric and unequal-mass binaries. Nearly equal-mass binaries behave similarly to their equal-mass counterparts: Prograde binaries inspiral, albeit somewhat slowly, and have their eccentricities damped; retrograde binaries inspiral ∼2–3 times faster than their prograde counterparts, and those with near-equal masses are driven quickly toward near-unity eccentricities. However, the primaries in retrograde binaries with mass ratios of m2/m1 ≲ 0.4 experience significantly weaker headwinds and retain substantial accretion disks that help damp binary eccentricities, slowing binary inspirals. Additionally, we find that while accretion drives prograde binaries toward equal masses thanks to the exchange of material between the primary and secondary accretion disks, retrograde binaries are driven slowly toward more extreme mass ratios. Prograde binaries, and generally those with low mass ratios, likely accrete for multiple e-folding timescales before merger. On the other hand, high-mass-ratio retrograde binaries may merge before accreting substantially, potentially approaching merger with detectable eccentricity. Future ground-based GW observatories, with their broader frequency coverage, should be particularly useful for studying these populations.

Keywords: Accretion, Black holes, Gravitational wave sources, Active galactic nuclei, Astrophysical fluid dynamics
Turbulent Heating in Collisionless Low-beta Plasmas: Imbalance, Landau Damping, and Electron─Ion Energy Partition. An understanding of how turbulent energy is partitioned between ions and electrons in weakly collisional plasmas is crucial for modeling many astrophysical systems. Using theory and simulations of a four-dimensional reduced model of low-beta gyrokinetics (the "Kinetic Reduced Electron Heating Model"), we investigate the dependence of collisionless heating processes on plasma beta and imbalance (normalized cross-helicity). These parameters are important because they control the helicity barrier, the formation of which divides the parameter space into two distinct regimes with remarkably different properties. In the first, at lower beta and/or imbalance, the absence of a helicity barrier allows the cascade of injected power to proceed to small (perpendicular) scales, but its slow cascade rate makes it susceptible to significant electron Landau damping, in some cases leading to a marked steepening of the magnetic spectra on scales above the ion Larmor radius. In the second, at higher beta and/or imbalance, the helicity barrier halts the cascade, confining electron Landau damping to scales above the steep "transition-range" spectral break, resulting in dominant ion heating. We formulate quantitative models of these processes that compare well to simulations in each regime, and combine them with results of previous studies to construct a simple formula for the electron─ion heating ratio as a function of beta and imbalance. This model predicts a "winner takes all" picture of low-beta plasma heating, where a small change in the fluctuations' properties at large scales (the imbalance) can cause a sudden switch between electron and ion heating.

Keywords: Interplanetary turbulence, Solar wind, Plasma astrophysics
The Atacama Cosmology Telescope: Machine-learning-driven Tools for Detecting Millimeter Sources in Timestream Preprocessing. We present a new pipeline utilizing machine learning for classifying short-duration features in raw time-ordered data (TOD) of cosmic microwave background survey observations. The pipeline, specifically designed for the Atacama Cosmology Telescope, works in conjunction with the previous TOD preprocessing techniques that employ statistical thresholding to indiscriminately remove all large spikes in the data, whether they are due to noise features, cosmic rays, or true astrophysical sources, in a process called "data cuts." This has the undesirable effect of excising real astrophysical sources, including transients, from the data. The classification pipeline demonstrated in this work uses the output from these data cuts and is able to differentiate between electronic noise, cosmic rays, and point sources, enabling the removal of undesired signals while retaining true astrophysical signals during TOD preprocessing. We achieve an overall accuracy of 90% in categorizing data spikes of different origin and, importantly, 94% for identifying those caused by astrophysical sources. Our pipeline also measures the amplitude of any detected source seen more than once and produces a subminute-to-minute light curve, providing information on its short-timescale variability. This automated pipeline for source detection and amplitude estimation will be particularly useful for upcoming surveys with large data volumes, such as the Simons Observatory.

Keywords: Classification, Cosmic microwave background radiation, Stellar flares, Transient detection, Random Forests
The Dependency of Bar Formation Timescale on Disk Mass Fraction, Toomre Q, and Scale Height. Bars are one of the most prominent galactic structures. The classical swing-amplification theory can qualitatively describe the spontaneous bar instability of stellar disks. Still, it cannot quantify the bar formation process or explain why some disk galaxies do not have a bar. Recent studies found that the bar formation timescale depends exponentially on the disk mass fraction of the host galaxy (dubbed as "Fujii relation"), but they only explored a limited parameter space, where the physical effects of Toomre Q (local disk stability parameter) and disk scale height of the host galaxies are not fully explored. In this work, we check the robustness of the Fujii relation in a higher-dimensional parameter space of disk mass fraction, Toomre Q, and scale height. We find that the Fujii relation holds for disk galaxies with physically reasonable Toomre Q and scale height. Furthermore, the bar formation timescale also approximately linearly depends on both Toomre Q and scale height, with a more prolonged bar formation in a hotter or thicker disk. We propose an empirical relation to combine the dependency of the bar formation timescale on the three parameters. Based on the empirical relation and recent observations, we estimate that the bar formation timescale in pure stellar disks ranges from  0.20‑0.06+0.09  to  12.20‑2.80+3.37  Gyr or even significantly beyond the Hubble timescale in some extreme cases.

Keywords: N-body simulations, Galaxy bars, Disk galaxies
The Orbital Period Changes for Novae. Cataclysmic variables (CVs) are close interacting binaries in which a white dwarf accretes materials from a low-mass main-sequence companion. CVs can experience nova eruptions due to low mass transfer rates. In the standard theory of CV evolution, the ejected materials during nova eruptions are assumed to leave the system in the form of fast, isotropic, optically thick winds, which predicts that novae only result in positive variation (expansion) of the orbital period (i.e., positive ΔP). In addition, the angular momentum losses (magnetic braking and gravitational radiation) only predict a steady long-term decay in the orbital period of CVs, i.e.,  Ṗ  is negative. Interestingly, an observation lasting over 30 yr reveals positive and negative values for both ΔP and  Ṗ  in CVs, strongly conflicting with the standard evolutionary patterns. However, it cannot be excluded that these observations originate from short-term phenomena caused by nova eruptions because of a short timescale of observations. In this paper, we model the effect of instantaneous nova eruptions on the evolution of CVs, considering three mechanisms associated with mass loss in nova eruptions, including fast wind, the Frank jet, and binary-driven mass loss. By assuming that the observed ΔP and  Ṗ  are dominated by short-term phenomena, our results show that the binary-driven mass loss can explain almost all of the observations of normal CVs. However, the Frank jet may be needed for some long-period CVs with evolved companions.

Keywords: Cataclysmic variable stars, Orbital evolution, Novae
Possible Neutrino Emission from the Pulsar Wind Nebula G63.7+1.1. We report on our finding of an excess of  54‑15+16  neutrinos at the location of the pulsar wind nebula (PWN) G63.7+1.1. By analyzing the IceCube track-like neutrino data for a group of 14 PWNe, which are selected as targets because of their reported association with molecular clouds, G63.7+1.1 is found to be the only one detected with neutrino emission, and the post-trail significance for the detection is 3.2σ. Previously, this PWN was estimated to have an age of ≳8 kyr, contain a candidate pulsar detected in X-rays, and have a distance of ∼6 kpc. More importantly, and related to the PWN's possible neutrino emission, surrounding molecular materials are seen to interact with the PWN. On the basis of these properties, we examine the proton–proton interactions as the process for the neutrino production. The PWN (or the pulsar) can provide sufficient energy to power the required high-energy (HE) protons. This possibly first neutrino-emitting case in our Galaxy, with problems or other possibilities to be solved or examined, may reveal to us that PWNe are the significant Galactic HE neutrino sources.

Keywords: Gamma-ray sources, Neutrino astronomy, Pulsars, Pulsar wind nebulae
Kinetic Simulations of the Cosmic-Ray Pressure Anisotropy Instability: Cosmic-Ray Scattering Rate in the Saturated State. Cosmic-ray (CR) feedback plays a vital role in shaping the formation and evolution of galaxies through their interaction with magnetohydrodynamic waves. In the CR self-confinement scenario, the waves are generated by the CR gyroresonant instabilities via CR streaming or CR pressure anisotropy and saturate by balancing wave damping. The resulting effective particle scattering rate by the waves, νeff, critically sets the coupling between the CRs and background gas, but the efficiency of CR feedback is yet poorly constrained. We employ 1D kinetic simulations under the magnetohydrodynamic-particle-in-cell framework with the adaptive δ f method to quantify νeff for the saturated state of the CR pressure anisotropy instability with ion-neutral friction. We drive CR pressure anisotropy by expanding/compressing the box, mimicking the background evolution of magnetic field strength, and the CR pressure anisotropy eventually reaches a quasi-steady state by balancing quasi-linear diffusion. At the saturated state, we measure νeff and the CR pressure anisotropy level, establishing a calibrated scaling relation with environmental parameters. The scaling relation is consistent with quasi-linear theory and can be incorporated to CR fluid models, in either the single-fluid or p-by-p treatments. Our results serve as a basis for accurately calibrating the subgrid physics in macroscopic studies of CR feedback and transport.

Keywords: Alfven waves, Magnetohydrodynamics, Plasma astrophysics, Cosmic rays