Sazuna/UAT_keywords huggingface dataset:
Modeling the Contact Surfaces Formed by Pebble Collisions: Application to Formation of Comet 67P/Churyumov─Gerasimenko. Modeling the contact surfaces formed by pebble collisions is crucial to understanding the formation process of comets, which are thought to be composed of pebbles. In this paper, we develop a new model to estimate the contact surface radius and the number of contact points as functions of collision velocity, and examine the formation process of comet 67P/Churyumov─Gerasimenko. Our model is based on the compressive strength of dust aggregates obtained from numerical simulations and assumes that all the impact energy of the pebbles is used for their mutual compression. We compare our model with numerical simulations of pebble collisions, in which we prepare the initial pebbles in the form of compressed dust aggregate spheres and measure the contact surface and pebble radii using two- and three-dimensional characteristic radii, respectively. We also apply our model to the formation scenario of comet 67P, whose tensile strength and bulk density have already been estimated in the literature. We find that its low tensile strength points to formation via pebble collisions at velocities below ∼10 cm s−1 when a microscopic filling factor of pebbles is lower than 0.6, suggesting that inelastic bouncing collisions played a role in damping the collision velocities. By assuming that the pebble collision velocity is determined by the transition velocity between bouncing and sticking, we estimate the pebble radius inside comet 67P to be 130 μm or smaller.

Keywords: Analytical mathematics, Computational methods, Planetesimals, Comets, Planet formation
Distance to the IBEX Ribbon beyond the Heliopause. Our understanding of the solar─interstellar interaction greatly improved with measurements of energetic neutral atoms (ENAs) from the outer heliosphere by NASA's Interstellar Boundary Explorer (IBEX). The IBEX mission measurements showed us the solar─interstellar interaction was far more complex than we originally thought. One such measurement was the Ribbon: a narrow, enhanced band of ENA emissions wrapped across the sky. We now generally understand its origin being outside the heliopause. This was confirmed, among other methods, using the astronomical method of parallax and temporal cross correlations with the solar wind output from the Sun. Here, we perform cross correlations of Ribbon ENAs with the solar wind to derive the distance to the Ribbon, and associated uncertainties, in two different sections of the sky (centered ∼30° below and ∼30° above the ecliptic plane). Parameters that introduce uncertainties include the neutral H density in the very local interstellar medium, the speed of the parent neutral particles that travel across the heliopause, and the cross correlation. We derive the distance to the Ribbon in these two spatially averaged sections, yielding distances of  dR  = 90 ± 56 and  dR  = 192 ± 42 au for the southern and northern sections of the Ribbon, respectively, or an average of 155 ± 34 au—a rough value one may use for the Ribbon source distance in the forward hemisphere of the heliosphere. Quantifying uncertainties is important for understanding the accuracy of these calculations as they can be a significant fraction of the calculated distance to the Ribbon itself.

Keywords: Heliopause, Heliosphere, Solar wind, Interstellar magnetic fields, Pickup ions, Interstellar medium
New Neutral─Neutral Pathways in the Chemistry of Silicon- and Sulfur-bearing Molecules in the Cold Interstellar Medium. Silicon is the most abundant third-row element in space and plays a major role in interstellar dust as silicate particles. Furthermore, silicon is important for the formation of silicate dust in oxygen-rich AGB stars and in supernova remnants. The formation and growth of such particles from the gas phase is a complex subject, believed to be initiated by molecules such as SiO and SiS. In this work we perform high-level electronic structure calculations on the SiSOH system, which allows us to shed light on the reactivity of several silicon and sulfur bearing species, such as SiO, SiS, SO, OH, HSiS, HSO, HSiO, and OSiS. We reveal several new neutral─neutral reaction pathways for formation and destruction that are predicted to occur without a potential energy barrier and thus be possible even in the coldest regions of the interstellar medium. We have found a new neutral─neutral destruction route for SiS (only destruction by atomic oxygen and carbon was previously known) and a possible explanation for the nondetection of OSiS, even though its rotational spectrum is well determined experimentally. Overall, we reveal 14 new relevant reactions and provide an estimate for their rate coefficients, which can be incorporated into astrochemical databases and models of the abundances of these molecules in space.

Keywords: Reaction rates, Chemical abundances, Astrochemistry
Spatially Resolved Transport Parameters in Solar Flares. The time profile of solar flare radio emission is often modeled as an injection of energetic particles onto a closed magnetic loop, where they may be trapped by the pinching of field lines and remain for a time before decaying through loss of energy to the background or escaping to the solar surface through the bottom of the loop. These injection, trapping, and precipitation models for energetic particle transport have often been used to explain the characteristics of spatially integrated microwave emissions in solar flares. With the high-cadence imaging spectroscopy capabilities of modern radio instruments, these ideas can be probed with new depth. Radio imaging allows for the selection of particular regions of flares to spatially and temporally isolate individual injections and determine individual decay parameters that could be confused in spatially integrated spectra. Simultaneous spectroscopy allows the fitting of light curves versus frequency for insight into the evolution of the particle energy spectrum and a deeper physical understanding of the decay process. Using currently available time resolution and data quality, injections and decays can be fit simultaneously to the order of 1 s. These considerations motivate the creation of the Pulsed-Injection-Precipitation Decomposition Fitter (PIP_Decomp), which implements an automated method for fitting a series of light curves with injection functions convolved with exponential decays to produce spectrally resolved fit parameters. Herein, PIP_Decomp is introduced and tested by applying it to model flares. Then, PIP_Decomp is used to investigate two relatively simple flares observed by the Expanded Owens Valley Solar Array.

Keywords: Solar radio flares, Solar flares, Solar flare spectra
ALMA Subparsec Resolution Dense Molecular Line Observations of the NGC 1068 Nucleus. We present the results of our ALMA observations of the dense molecular HCN J = 4─3 and HCO+ J = 4─3 lines at ≲1 pc (≲14 mas) resolution in the nuclear region of the nearby (∼14 Mpc) well-studied AGN NGC 1068. Both emission lines are clearly detected around the AGN along an almost east─west direction, which we ascribe to the dusty molecular torus. The HCN J = 4─3 emission is brighter than the HCO+ J = 4─3 emission in the compact (≲3─5 pc) torus region. Apparent counterrotation between the inner (≲2 pc) and outer (≳2 pc) parts of the western torus, previously seen in ∼1.5 pc-resolution HCN J = 3─2 and HCO+ J = 3─2 data, is also confirmed in our new ≲1 pc-resolution HCN J = 4─3 and HCO+ J = 4─3 data. We apply a physically counterrotating torus model, in which a compact dense gas clump collided with the western side of the existing rotating torus from the opposite direction, and we find that this model largely reproduces the observed properties of the combined new ≲1 pc-resolution HCN J = 4─3 and HCO+ J = 4─3 data, and the previously obtained ≲1.5 pc-resolution HCN J = 3─2 and HCO+ J = 3─2 data.

Keywords: Molecular gas, Supermassive black holes, Millimeter astronomy, Active galaxies, Molecular spectroscopy, Water masers, Active galactic nuclei, Submillimeter astronomy, Radio interferometry, Interferometry
Investigation of Turbulent Fluctuations in the Fast and Alfvénic Slow Solar Wind at 1 au. We study the turbulent modes present in the Alfvénic slow and fast solar wind. This analysis focuses on two solar wind intervals: 2022 January 26─29 and February 6─9, and it is based on wind observations at 1 au. Our study examined Alfvénic slow with β &lt; 1 and fast solar wind with β &lt; 1 (∼O(1)), employing a superposed epoch analysis (SEA) to investigate the different turbulent modes and their power spectral densities. We find that the density fluctuations in Alfvénic slow and fast solar wind are primarily fast magnetosonic (MS) modes, although they differ in the dominant propagation direction of fast MS modes—forward propagating in the Alfvénic slow and backward propagating in the fast solar wind. In the Alfvénic slow regime, the SEA shows that the incompressible velocity fluctuations dominate the compressible contributions from fast and slow MS modes. The relative power of velocity fluctuations is largest in backward Alfvén propagating modes, ∼28.8% of the total velocity fluctuations energy. The wavenumber anisotropy of the fast MS modes associated with density fluctuations is k⊥ ≫ k∥. In the fast solar wind, compressible velocity fluctuations are dominated by fast MS mode, with the velocity fluctuation energy of 43.6% in backward and 42.0% in forward components, surpassing the contributions from the incompressible Alfvénic fluctuations. We find that magnetic field fluctuations are predominantly associated with magnetic island modes, contributing 53.9% of the total magnetic fluctuations energy in the Alfvénic slow and 35.4% in the fast solar wind.

Keywords: Interplanetary turbulence, Space plasmas, Magnetohydrodynamics, Solar wind
The Concordance of Weak Lensing and Escape-velocity Mass Estimates for Galaxy Clusters. In the Λ cold dark matter paradigm, the masses of the galaxy clusters inferred using background galaxies via weak-lensing shear should agree with the masses measured using the galaxy projected radius─velocity phase-space data via the escape velocity profile. However, prior work indicates that the correlation between caustic-inferred escape masses and weak lensing masses is statistically consistent with zero. Based on recent advancements in the measurement of the escape edge and its physical interpretation, we conduct a revised comparison between these two independent mass inference techniques for 46 galaxy clusters between 0.05 ≤ z ≤ 0.3 and over an order of magnitude in mass,  14.4≤log10M/M⊙≤15.4 . We find excellent agreement, with a correlation ( 0.679−0.049+0.046 ), and a mean relative difference between the two mass measurements consistent with zero (0.02 ± 0.02 dex). The observed scatter between these direct mass estimates is 0.17 dex and is consistent with the reported individual mass errors, suggesting that there is no need for an additional intrinsic component. We discuss the important practical consequences of these results, focusing on the systematic uncertainties inherent to each technique, and their implications for cosmology.

Keywords: Galaxy clusters, Orbital motion, Weak gravitational lensing, Cosmological parameters, Gravitation, Observational cosmology, Galaxy groups, N-body simulations, Dark matter, Dark energy
In Situ Formation of the Cold Classical Kuiper Belt. Cold classical Kuiper Belt objects (CCKBOs) are considered first-generation planetesimals that formed 42─47 au from the Sun and have remained untouched since. Formation is thought to proceed by clumping of dust particles in protoplanetary disk gas by the streaming instability, followed by gravitational collapse. Previous calculations along these lines are inconsistent with the CCKB's supposedly pristine nature, because they assume orders-of-magnitude more solid mass than is actually present in the CCKB (a few thousandths of an Earth mass) and do not explain how to expel the &gt;99% extra mass. Here we show from 3D numerical simulations of dust and gas that the total mass in CCKBOs, their characteristic sizes of ∼100 km, and the relative proportion of prograde to retrograde binaries can all be reproduced at the tail end of the solar nebula's life, when it contained just 2%─5% of its original (minimum-mass) gas. As a solar metallicity's worth of millimeter-sized solids drains out from 42 to 47 au from nebular headwinds, about 1% of the dust collapses into planetesimals that remain behind in the CCKB region. Binarity is guaranteed from a simple analytic estimate, confirmed numerically, of the spin angular momentum in clumps seeded by the streaming instability. We show that other formation scenarios, including trapping of dust within a gas pressure bump, fail to reproduce the low-mass CCKB. Outstanding problems are identified.

Keywords: Small Solar System bodies, Classical Kuiper belt objects, Hydrodynamics, Protoplanetary disks, Planetesimals, Planet formation
Mid-infrared Extinction toward the Galactic Center. We determine the mid-infrared (MIR, ∼5─22 μm) extinction toward the Galactic center using MIRI/Medium-Resolution Spectrometer (MRS) integral field unit observations of the central 3″ × 3″ region (near 5 μm) to 7″ × 7″ region (near 22 μm). To measure the MIR extinction, we employ two approaches: modeling the intrinsic-to-observed dust thermal spectrum and assessing the differential extinction between hydrogen recombination lines. Expanding on prior work, we directly model the dust-opacity distribution along the line of sight, and we make available a Python code that provides a flexible tool for deriving intrinsic dust emission spectra. We confirm the spatial variability of extinction across the field, demonstrating that dusty sources—such as IRS 29N—exhibit higher local extinction. Furthermore, we verify the absence of emission features from polycyclic aromatic hydrocarbons in the MIR spectra of the Galactic center. Using the two complementary methods, we derive a refined "best guess" MIR extinction law for Sgr A* and the surrounding Galactic-center region. By applying the extinction law to an MIR flare measurement discussed in a companion paper, we estimate a residual relative extinction uncertainty for the short MIRI/MRS grating of the order of 0.2 mag from ∼5 to ∼18 μm and ∼0.3 mag from ∼18 to ∼22 μm, consistent with our uncertainty estimate.

Keywords: Milky Way Galaxy physics, Galactic center, Interstellar dust extinction
Radio Observations Point to a Moderately Relativistic Outflow in the Fast X-Ray Transient EP241021a. Fast X-ray transients (FXRTs) are short-lived X-ray outbursts with diverse progenitor scenarios, including compact object mergers, stellar core collapses, and tidal disruption events. The Einstein Probe (EP) has enabled the rapid discovery and follow-up of dozens of FXRTs, revealing that while some of them overlap with traditional gamma-ray bursts (GRBs), a larger fraction of FXRTs have no associated gamma-ray counterpart down to deep limits. The origin of these gamma-ray dark FXRTs and their connection to the diverse landscape of stellar explosions remains an open question, which can be tackled through the study of their multiwavelength counterparts and environment. In this paper, we present long-term radio observations of the gamma-ray dark EP241021a, which exhibits sustained radio emission for over 100 days, placing it among the longest-lived radio afterglows. We detect signature of interstellar scintillation in early epochs, allowing us to constrain the angular size and Lorentz factor of the emitting region. Our observations point to an outflow that is at least mildly relativistic with Γ ≳ 4. Afterglow modeling favors a moderately relativistic (Γ ≍ 40) top-hat jet (θc ≍ 0.16 rad) interacting with a low-density interstellar medium. The derived beaming-corrected kinetic energy, Ek ∼ 1.6 × 1051 erg, and low radiative efficiency, ηγ ≲ 1%, are consistent with a standard relativistic explosion which did not produce bright gamma rays. Alternatively, a highly relativistic (Γ ≳ 100) structured jet remains consistent with our observations if seen substantially off-axis (θobs &gt; θc). In the latter case, the initial X-ray flare detected by EP would be caused by the lower-Γ ejecta from the lateral wings intercepting our line of sight rather than by traditional prompt-emission mechanisms within the jet core.

Keywords: Radio transient sources
SPYGLASS. VII-A. The Demographics and Ages of Small Nearby Young Associations. Recent Gaia-based young stellar association surveys have revealed dozens of low-mass populations that have, until recently, been too small or sparse to detect. These populations represent a largely unstudied demographic with unknown origins, and their relative isolation may minimize gravitational disruptions that impact traceback, making them compelling targets for dynamical studies. In this paper, we survey 15 of these isolated young associations for the first time: Andromeda South (SCYA-97), Aquila East, Aries South (SCYA-104), Cassiopeia East (SCYA-43), Canis Major North, Leo Central (SCYA-2), Leo East (SCYA-3), Theia 72, Ophiuchus Southeast, Scutum North (SCYA-70), Taurus-Orion 1 (TOR1), Theia 78, Vulpecula East (UPK 88), SCYA-54, and SCYA-79. By combining Gaia astrometry and photometry with new ground-based spectroscopic measurements, we assess the membership of each population, search for substructure, analyze their demographics, and compute ages. We find that the smallest populations in our sample contain &lt;20 M⊙ of stellar mass, making them the smallest associations ever detected. Four host substantial substructure, including TOR1, where we discover TOR1B, a new 16 M⊙ association with radial velocities inconsistent with an origin in the parent complex. Using PARSEC isochrones, we produce self-consistent ages for all populations supported by dynamical and lithium depletion ages, which range from 6.9 ± 0.5 Myr in TOR1A to 42.8 ± 2.4 in AndS. Our results provide the first detailed overview of the properties of these populations, characterizing a largely unknown category of young associations that may have an important role in tracing the processes that guide local star formation.

Keywords: Stellar ages, Stellar astronomy, Pre-main sequence stars, Star formation, Stellar associations
Callisto's Nonresonant Orbit as an Outcome of Circum-Jovian Disk Substructure. The Galilean moons of Io, Europa, and Ganymede exhibit a 4:2:1 commensurability in their mean motions, a configuration known as the Laplace resonance. The prevailing view for the origin of this three-body resonance involves the convergent migration of the moons, resulting from gas-driven torques in the circum-Jovian disk wherein they accreted. To account for Callisto's exclusion from the resonant chain, a late and/or slow accretion of the fourth and outermost Galilean moon is typically invoked, stalling its migration. Here, we consider an alternative scenario in which Callisto's nonresonant orbit is a consequence of disk substructure. Using a suite of N-body simulations that self-consistently account for satellite-disk interactions, we show that a pressure bump can function as a migration trap, isolating Callisto and alleviating constraints on its timing of accretion. Our simulations position the bump interior to the birthplaces of all four moons. In exploring the impact of bump structure on simulation outcomes, we find that it cannot be too sharp nor flat to yield the observed orbital architecture. In particular, a "Goldilocks" zone is mapped in parameter space, corresponding to a well-defined range in bump aspect ratio. Within this range, Io, Europa, and Ganymede are sequentially trapped at the bump, and ushered across it through resonant lockstep migration with their neighboring, exterior moon. The implications of our work are discussed in the context of uncertainties regarding Callisto's interior structure, arising from the possibility of non-hydrostatic contributions to its shape and gravity field, unresolved by the Galileo spacecraft.

Keywords: Planetary migration, Galilean satellites, Planetary-disk interactions
PASSAGES: The Discovery of a Strongly Lensed Protocluster Core Candidate at Cosmic Noon. Investigating the processes by which galaxies rapidly build up their stellar mass during the peak of their star formation (z = 2─3) is crucial to advancing our understanding of the assembly of large-scale structures. We report the discovery of one of the most gas- and dust-rich protocluster core candidates, PJ0846+15 (J0846), from the Planck All-Sky Survey to Analyze Gravitationally lensed Extreme Starbursts (PASSAGES) sample. The exceedingly high total star formation rate (SFR) uncorrected for lensing magnification ( μ) of μSFR  =39900−12900+23000M⊙  yr−1 is the result of a foreground cluster lensing at least 11 dusty star-forming galaxies between z = 2.660 and 2.669, where the intrinsic value is estimated to be SFR  =5200−2000+3200M⊙  yr−1. Atacama Large Millimeter/submillimeter Array observations uncovered 18 CO(3─2) emission-line detections, some of which are multiply imaged systems, lensed by a foreground cluster at z = 0.77. We present the first multiwavelength characterization of this field, constructing a lens model that predicts that these 11 galaxies (μ ≃ 1.5─25) are contained within a projected physical extent of 280 × 150 kpc, with a velocity dispersion of σv = 246 ± 72 km s−1. J0846 exhibits the rare case of a protocluster candidate whose core is strongly lensed, offering a magnified view of the rapid stellar buildup within an overdense environment at Cosmic Noon.

Keywords: Starburst galaxies, Protoclusters, Strong gravitational lensing, Galaxy evolution, Interstellar medium
DESI Spectroscopy of HETDEX Emission-line Candidates. I. Line Discrimination Validation. The Hobby─Eberly Dark Energy Experiment (HETDEX) is an untargeted spectroscopic galaxy survey that uses Lyα-emitting galaxies (LAEs) as tracers of 1.9 &lt; z &lt; 3.5 large-scale structure. Most detections consist of a single emission line, whose identity is inferred via a Bayesian analysis of ancillary data. To determine the accuracy of these line identifications, HETDEX detections were observed with the Dark Energy Spectroscopic Instrument (DESI). In two DESI pointings, high-confidence spectroscopic redshifts are obtained for 1157 sources, including 982 LAEs. The DESI spectra are used to evaluate the accuracy of the HETDEX object classifications and tune the methodology to achieve the HETDEX science requirement of ≲2% contamination of the LAE sample by low-redshift emission-line galaxies, while still assigning 96% of the true Lyα emission sample with the correct spectroscopic redshift. We compare emission-line measurements between the two experiments assuming a simple Gaussian line fitting model. Fitted values for the central wavelength of the emission line, the measured line flux, and line widths are consistent between the surveys within uncertainties. Derived spectroscopic redshifts, from the two classification pipelines, when both agree as an LAE classification, are consistent to within &lt;∆z/(1 + z)&gt; = 6.9 × 10−5 with an rms scatter of 3.3 × 10−4. Data are available at https://data.desi.lbl.gov/desi/public/dr1/vac/dr1/hetdex.

Keywords: Astronomical methods, Redshift surveys