Sazuna/UAT_keywords huggingface dataset:
Causal Relationship between Current Sheet Flapping, Electron-only Reconnection, and Ion-coupled Reconnection. Magnetic reconnection is a fundamental physical process operating throughout the Universe, yet its onset in planetary magnetotails remains elusive. Current-sheet flapping is a common dynamic phenomenon in planetary magnetotails, with its roles in driving reconnection largely underexplored. This paper reports the first observation of electron-dominant and ion-coupled reconnection accompanied by current sheet flapping. The Magnetospheric Multiscale mission (MMS) spacecraft was located in the premidnight sector current sheet, which was undergoing kink-mode flapping that propagated duskward, away from the midnight sector, with a frequency of 0.06─0.1 Hz and a wavelength of around 0.5 RE. The flapping led MMS to cross the current sheet repeatedly, from north to south and vice versa. During the initial crossing of the current sheet, distinct electron outflows were observed, while ion responses were weak. This indicates either electron-only reconnection, suggesting an early stage of reconnection (temporal effect) or MMS passing through the exhaust region close to an X-line (spatial effect). Signatures of the electron diffusion region's limited length, yielding an unusually high aspect ratio, suggest that the former scenario is more likely. Regular ion-coupled reconnection that involves ion outflows became more prominent until MMS eventually crossed the X-line from tailward to earthward. This event indicates a potential causal relationship between electron-only reconnection, current sheet flapping, and subsequent ion reconnection. We discuss feasible mechanisms for current sheet flapping and the feedback between flapping and reconnection, providing new insights into the onset of magnetotail reconnection and cross-scale processes of importance to other heliospheric and astrophysical systems.

Keywords: Space plasmas, Planetary magnetospheres, Solar magnetic reconnection, Plasma physics
Impact of Propagation Effects on the Spectro-temporal Properties of Fast Radio Bursts. We present a mathematical analysis of propagation-induced distortions in the spectro-temporal properties of fast radio bursts (FRBs). Within the triggered relativistic dynamical model, we derive a centroid-based formulation of the sub-burst slope law, which describes an inverse relation between the sub-burst frequency drift rate and the intrinsic temporal width tw. We extend this framework to include two frequency-dependent propagation effects: (i) multipath scattering, characterized by a pulse-broadening timescale τsc ∝ ν−4, and (ii) residual dispersion, parameterized by ∆DM ∝ ν−2. Our analysis shows that scattered bursts exhibit the same qualitative inverse slope─duration relation but differ quantitatively through a larger scaling coefficient when τsc &gt; tw. Residual DM errors act asymmetrically: under-dedispersion flattens the sub-burst slope, whereas over-dedispersion produces a nonlinear increase and eventual sign change. When both effects are present, scattering counterbalances the steepening induced by over-dedispersion and augments the flattening from under-dedispersion, yielding characteristically distorted curves. We repeat analysis for ultrashort duration bursts (ultra-FRBs) with tw = 50 μs at 1 GHz and find them to be far more sensitive to propagation errors. Deviations become measurable for  ∆DM∼0.05  pc cm−3 and for τsc ∼ 0.1 ms at 1 GHz, levels that have negligible impact on the standard-width sub-bursts. Our analysis provides practical diagnostics to disentangle propagation effects from observed spectro-temporal properties, thereby recovering intrinsic correlations among FRB parameters.

Keywords: Computational astronomy, Analytical mathematics, Intergalactic medium, Interstellar scattering, Radio transient sources
MUSE Study of Two Giant Low-surface-brightness Galaxies with Compact Satellites. Giant low-surface-brightness galaxies (gLSBGs) are rare objects with disk radii up to 160 kpc and dynamical masses of up to the order of 1012 M⊙. Their very existence challenges currently accepted theories of galaxy formation and evolution, as it is difficult to build such large, dynamically cold disks through mergers without destroying them. We present deep MUSE mosaic observations of two nearby gLSBGs with compact elliptical satellites: UGC 1382, which hosts a globally counterrotating gaseous disk, and AGC 192040, which does not. We analyze properties of ionized gas and present spatially resolved maps of kinematics and metallicity, as well as stellar population analysis for the central regions of the galaxies. The radial gradients of gas-phase metallicities are flat for both galaxies. Our observational data indicate that both galaxies experienced mergers several Gyr ago. However, the scenarios of the formation of giant disks appear to be slightly different for these two systems. For AGC 192040, we propose gas accretion from the filament or from the cooling hot halo gas followed by a merger with a companion on a prograde orbit at an intermediate mass ratio. For UGC 1382, multiple gas-rich mergers with companions on retrograde orbits are preferred by the data.

Keywords: Disk galaxies
A Quenched and Relatively Isolated Dwarf Galaxy in the Local Volume. An increasing number of discoveries of isolated and quenched dwarf galaxies are challenging the idea that the present-day local environment of low-mass systems is the main determinant of their quenching. We present new Hubble Space Telescope (HST) data of one such system, the dwarf galaxy Canes Venatici C (CVnC). CVnC is a low-mass ( 3.4−2.6+4.2×106M⊙ ) galaxy with a Tip of the Red Giant Branch distance of  8.43−0.32+0.47  Mpc determined from the resolved stars in the HST imaging, which we also use to derive CVnC's structural parameters. CVnC's distance places CVnC in the Local Volume and in an isolated environment with the most tidally influential L⋆ galaxy &gt; 5Rvir away. Additional constraints from the HST color─magnitude diagram, archival far-ultraviolet, and neutral hydrogen (H I) data show that CVnC is quenched, with no evidence of star formation in the last 100 Myr and no detectable gas (MH I &lt; 1.5 × 106 M⊙). Circumstantial evidence suggests that CVnC may have quenched via past interactions with the L⋆ galaxy NGC 4631 (LK = 1010.4 L⊙), and was possibly sent on an extreme backsplash orbit by the tidal dissolution of a subhalo group. However, other quenching mechanisms—such as stripping via the cosmic web—cannot be ruled out. CVnC adds to the growing number of quenched dwarf galaxies in underdense environments, a population that will be critical to defining the mass and environment regimes in which different quenching mechanisms operate.

Keywords: Hertzsprung Russell diagram, Galaxy environments, Stellar populations, Dwarf galaxies, HST photometry, Galaxy quenching
Surface Interactions in Photon Monte Carlo Simulations. We implement a comprehensive simulation of photon surface interactions using a Monte Carlo approach. This is effective in simulating the interaction of light with telescope mirrors and lenses. We use a full electromagnetic solution to simulate the wavelength and angular dependence at surfaces. This includes bare interfaces, monolayer interfaces, protected layer coatings, and multilayer coatings. We handle special cases when multilayer data are incomplete or when there is photoconversion in the interface as with sensors. We implement interactions with surface microroughness and predict the corresponding angular distribution using a Monte Carlo implementation of the Harvey─Shack scatter theory for a microroughness power spectrum. Finally, we simulate surface interaction with contamination from dust or condensation using Mie scattering applied efficiently to individual contaminants. The combination of these implementations can efficiently simulate rough to polished surfaces of arbitrary materials that are fully cleaned or dusty. The observational consequences include complex wavelength- and spatial-dependent photometric errors, the dominant effect of the wings of point-spread functions (PSFs), dust rings, and wavelength- and angle-dependent throughput losses. We find agreement with the PSF wings of WIYN One Degree Imager observations of bright stars and the properties of dust rings, and demonstrate the ability to disentangle mirror microroughness from the turbulence PSF patterns. The comprehensive numerical implementation of surface interactions has wide applicability in nonastronomical applications as well.

Keywords: Observational astronomy, Primary mirror, Astronomical simulations, Lenses
Super-Eddington Accretion onto Black Holes and Its Application to Fallback Accretion. We study the problem of steady-state spherical accretion onto a black hole, in which the internal energy of the flow is governed by radiation and photon diffusion dominates the energy flux at large radii. In the freefall limit, the fluid equations can admit two types of solutions for a given accretion rate: (1) accretion flows that become isothermal at large radii, and (2) solutions in which the temperature at infinity vanishes as a power law of the radius. Using boundary-layer theory, we obtain analytic solutions for the two cases and apply our results to fallback accretion onto a black hole following a failed supernova (SN) explosion. We give predictions for the observational signature of fallback accretion using realistic progenitor properties from MESA, both for a fully ionized inflow and for the more realistic case in which recombination/ionization take place due to low photospheric temperatures. The observed fading sources coincident with the failed-SNe candidates in NGC 6946 and M31 are too luminous to be powered by spherical accretion onto newly formed black holes; the observed sources are instead likely due to accretion of the turbulent, convective envelope of the supergiant progenitor.

Keywords: Supernovae, Astrophysical black holes
Numerical Simulations of the Circularized Accretion Flow in Population III Star Tidal Disruption Events. I. The Accretion Flow and the Wind. Tidal disruption events (TDEs) have recently been proposed as potential probes for Population III (Pop III) stars. However, the properties of the accretion flow and the wind from the Pop III star TDE system are not clear. By performing radiative hydrodynamic simulations, we study the "circularized" accretion flow of the Pop III star TDE system. The masses of the black hole (BH) and the disrupted star are 106 and 300 solar masses, respectively. We focus on the properties of the wind. We find that the BH accretion rate is highly super-Eddington. A strong wind is driven by radiation pressure. Due to the presence of a strong wind, only 25%─35% of the fallback debris is accreted by the BH. The remaining part is taken away by the wind. The kinetic power of the wind can be as high as 1046 erg s−1. The properties of the wind obtained in this paper may be useful for understanding the radiation properties of Pop III star TDEs in the context of the wind "reprocessing" model.

Keywords: Accretion, Black hole physics, Supermassive black holes, Population III stars, Hydrodynamics, Tidal disruption, Galaxy accretion disks
Evidence for the Transition from Thermal to Nonthermal Emission in the Prompt Emission of GRB 161117A. GRB 161117A is a long-duration gamma-ray burst with three main overlapping peaks. By analyzing the time-resolved spectra of its data observed with the Gamma-Ray Burst Monitor on board the Fermi mission, we find that the spectral evolution shows a transition from thermal (single blackbody, hereafter BB) to hybrid (power-law, hereafter PL, +BB), and finally to nonthermal (Band and cutoff PL) emissions. Such a transition suggests that the jet composition of GRB 161117A should be changed from a fireball to a Poynting-flux-dominated jet. The bulk Lorentz factor (Γph), radii (Rph and R0), magnetization factor at the central engine (σ0), and dimensionless entropy (η) of the outflow can be inferred by invoking the observed quasi-thermal component within two models (e.g., pure fireball and hybrid). It is found that Γph seems to be tracking with the light curve, and R0 remains a constant at ∼ 108 cm. The low magnetization (1 + σ0 ∼ 1) and high dimensionless entropy (η ≫ 1) during the first seven time-intervals suggest it to be a pure fireball outflow. Moreover, we also estimate the lower limit of magnetization parameters at the photosphere radius (σph ∼ 1.4 and 0.75) for late phase via the nonthermal spectra, and it indicates that the particle acceleration mechanism is dominated by internal shocks rather than magnetic dissipation processes. Finally, the  νν̄  annihilation mechanism of NDAF model to explain the thermal emission of GRB 161117A is also discussed.

Keywords: Gamma-ray bursts
A Solution to the Tension of Burning on Neutron Stars and Nuclear Physics. When neutron stars accrete matter from a companion star, this matter forms a disk around them and eventually falls on their surface. Here, the fuel can ignite into bright flashes called Type I bursts. Theoretical calculations based on state-of-the-art nuclear reactions are able to explain many features of the bursts. However, models predict that the bursts should cease at high accretion rates, whereas in many sources they disappear at much lower rates. Moreover, their recurrence times also show strong discrepancies with predictions. Although various solutions have been proposed, none can account for all the observational constraints. Here, we describe a new model that explains all the contradictory behaviors within a single picture. We are able to reconstruct the conditions on the star surface that determine the burst properties by comparing data to new simulations. We find strong evidence that the physical mechanism driving the burst behavior is the structure of the accretion disk in the regions closest to the star. This connection reconciles the puzzling burst phenomenology with nuclear physics and also opens a new window on the study of accretion processes around compact objects.

Keywords: Neutron stars, X-ray binary stars, Accretion, X-ray bursts
Unveiling the Ionized and Neutral ISM at z &gt; 10: The Origin of [O III] /[C II] Ratios from a Subparsec Resolution Radiative Transfer Simulation. Recent multiwavelength observations by JWST and the Atacama Large Millimeter/submillimeter Array (ALMA) are unveiling both ionized and neutral interstellar medium (ISM) components in high-redshift (z &gt; 6) galaxies. In this work, we investigate the origin of rest-frame far-infrared [O III] 88 μm and [C II] 158 μm emission by performing zoomed-in cosmological simulations of dwarf-galaxy progenitors at z = 9─13. Our simulations incorporate on-the-fly radiative transfer at subparsec (∼ 0.1 pc) resolution, allowing us to resolve the multiphase ISM. We compute emission lines on a cell-by-cell basis, taking into account local temperature, density, metallicity, radiation field strength, column density, and spectral hardness of radiation bins. We find that [O III] predominantly arises from centrally located ionizing bubbles with temperatures of ∼(1─5) × 104 K and high-ionization parameters of  logUion≃−1.5 . In contrast, [C II] is produced in the surrounding dense neutral regions at ∼5 × 103 K, which are heated by strong far-UV radiation (G/G0 ∼ 103−5) from the central stellar clusters. This spatial arrangement leads to large local variations in [O III] /[C II], ranging from ∼100─0.01. Our galaxy reproduces the global ratio [O III] /[C II] ∼5─30, consistent with recent ALMA detections at z &gt; 6 without invoking enhanced O/C abundance ratios. We further derive that [O III] /[C II] linearly scales with the mass and density ratios of ionized to neutral gas, MH II/MH I and nH II/nH I and show that the [O III] /[C II] ratio typically changes from 5.7 to 0.3 from high-z to low-z. For future synergies of JWST and ALMA, we derived MH II/MH I for observed z &gt; 6 galaxies using Hβ and [C II] and show the validity of our scaling relations.

Keywords: Galaxy formation, High-redshift galaxies, Galaxy evolution, Interstellar medium
Infrared Spectral Energy Distribution Modeling of Velocity Excess in Maser Sources: Identifying Incipient Water Fountain Candidates. We investigated whether "velocity excess" in circumstellar maser lines can diagnose the earliest evolutionary phases of water fountains (WFs). Here, we define "velocity excess" as maser emission (e.g., H2O 22.235 GHz or OH 1665/1667 MHz) detected at velocities outside the velocity range of the OH 1612 MHz line, which traces the terminal expansion velocity of a spherical circumstellar envelope (CSE). Such excess velocities serve as an indicator of gas motions deviating from spherical expansion and may signify the onset of asymmetric outflows. Based on recent studies, we analyzed 17 sources showing velocity excess and fitted their infrared spectral energy distributions (SEDs) with the one-dimensional radiative transfer code DUSTY. Seven sources are well reproduced, implying outer CSEs that remain nearly spherical despite inner asymmetries. Among these, five exhibit single-peaked, asymptotic giant branch (AGB)-like SEDs, and two show double-peaked, post-AGB-like profiles. Infrared Astronomical Satellite (IRAS) variability indices and NEOWISE-R light curves reveal pulsations (∼600─1000 days) in three sources, supporting their AGB classification. Considering the magnitude of the velocity excess, two objects—IRAS 19229+1708 and IRAS 19052+0922—may represent the earliest or incipient WF phase, in which asymmetric outflows are beginning to emerge within otherwise spherical envelopes. These results support a morphological sequence in which bipolar jets and tori arise first in the central regions while the outer CSE remains spherical, and they show that selecting WF candidates via velocity excess effectively identifies objects at the onset of jet formation and early morphological transformation.

Keywords: Circumstellar masers, Evolved stars
Evolution of a Long-lived Deep-seated Main-sequence Magnetic Field during White Dwarf Cooling. We study the evolution of white dwarf (WD) magnetic fields that originate from convective-core dynamos during the main sequence. Using stellar evolution and WD cooling models combined with magnetic field diffusion calculations, we demonstrate that a surviving field from the main sequence can account for various features observed in magnetic WDs. In particular, the earlier emergence of stronger magnetic fields in more massive WDs, compared to older, less massive, and less magnetic ones, can be explained by this framework. This is because the magnetic boundary at the onset of WD cooling lies deeper in less massive WDs, resulting in a slower and weaker evolution of the surface magnetic field due to increasing electrical conductivity over time. We further show that many of the magnetic field strengths observed across different WD samples can be reproduced if the deep-seated field generated during the main sequence is comparable to predictions from magnetohydrodynamic simulations of convective-core dynamos, or if equipartition provides a valid scaling for the main-sequence dynamo. Additionally, our predictions for surface magnetic fields vary by a factor of 2 to 4 when higher-order modes of poloidal magnetic field expansion and turbulent diffusion driven by crystallization-induced convection are included. These effects should therefore be considered when investigating the origin of magnetic fields in individual WDs.

Keywords: Stellar interiors, White dwarf stars, Stellar magnetic fields, Stellar evolution
Predicting Dust Temperature from Molecular Line Data Using Machine Learning. We have conducted experiments with machine learning techniques to construct dust temperature maps from the CO isotopolog molecular line data in the Orion A molecular cloud. In classical astrophysical methodology, multiband continuum data are required to derive the dust temperature. The present study aims to investigate the capability and limitations of machine learning techniques in deriving dust temperatures in regions without multiband dust continuum data. We have investigated how the number of pixels used for training influences the prediction accuracy and how the dust temperatures sampled in the training area influence the prediction accuracy. We find that ∼5% of the total number of pixels in the observational region is sufficient for training to obtain accurate predictions. Furthermore, a dust temperature sample within the training area should cover the whole temperature range and have a similar sample distribution to that of the entire observing region for an accurate prediction. The 12CO/13CO ratio is often found to be the most important feature in predicting the dust temperature. As the 12CO/13CO ratio is a tracer of photon-dominated regions (PDRs), the machine learning technique could connect the dust temperatures to PDRs. We also find that the condition of the thermal gas─dust coupling is not required for the accurate prediction of the dust temperature from the molecular line data and that machine learning is capable of capturing more information than classical astrophysical concepts.

Keywords: Star forming regions, Molecular clouds, Dust continuum emission, Interstellar medium, CO line emission
On the Origin of Intracluster Light Based on the High-resolution Simulation, NEWCLUSTER. Intracluster light (ICL) is a key component of galaxy clusters, with the potential to trace their dynamical assembly histories and the underlying dark matter distribution. Despite these prospects, its faint nature makes a consensus on its origin or population properties difficult to achieve, both in observations and simulations. In the hope of finding a breakthrough, we utilize the ongoing high-resolution cluster simulation, NEWCLUSTER. By classifying billions of particles in and around the cluster with a rigorous tracking procedure, we find that the majority of the ICL originates from satellites, including surviving and disrupted galaxies. Another notable finding is that the preprocessed component follows the density profile of dark matter better than the other components and has distinctive properties: old age, low metallicity, and enhanced α-element abundance. We further investigate the orbital dynamics, and our results demonstrate that the stripped fraction of satellites is primarily determined by the time since infall and the pericenter distance. By linking the demographic, chemical, and orbital properties of ICL stars to their origins, this work proposes a quantitative approach for tracing the assembly history of galaxy clusters from the ICL.

Keywords: Galaxy clusters, Hydrodynamical simulations, Galaxy formation, Tidal disruption, Galaxy evolution