Sazuna/UAT_keywords huggingface dataset:
Splitting and Eruption of an Active Region Filament Caused by Magnetic Reconnection. To gain a deeper understanding of the intricate process of filament eruption, we present a case study of a filament splitting and erupting by using multiwavelength data of the Solar Dynamics Observatory. It is found that the magnetic reconnection between the filament and the surrounding magnetic loops resulted in the formation of two new filaments, which erupted successively. The observational evidence of magnetic reconnection, such as the obvious brightening at the junction of two different magnetic structures, the appearance of a bidirectional jet, and subsequent filament splitting, were clearly observed. Even though the two newly formed filaments experienced failed eruptions, three obvious dimmings were observed at the footpoints of the filaments during their eruptions. Based on these observations, it is suggested that magnetic reconnection is the trigger mechanism for the splitting of the original filament and the subsequent eruption of the newly formed filaments. Furthermore, the process of filament splitting dominated by magnetic reconnection can shed light on the explanation of double-decker filament formation.

Keywords: Solar prominences, Solar magnetic reconnection, Solar filaments, Solar magnetic fields, Solar activity
A Multiwavelength, Multiepoch Monitoring Campaign of Accretion Variability in T Tauri Stars from the ODYSSEUS Survey. III. Optical Spectra. Classical T Tauri Stars (CTTSs) are highly variable stars that possess gas- and dust-rich disks from which planets form. Much of their variability is driven by mass accretion from the surrounding disk, a process that is still not entirely understood. A multiepoch optical spectral monitoring campaign of four CTTSs (TW Hya, RU Lup, BP Tau, and GM Aur) was conducted along with contemporaneous Hubble Space Telescope (HST) UV spectra and ground-based photometry in an effort to determine accretion characteristics and gauge variability in this sample. Using an accretion flow model, we find that the magnetospheric truncation radius varies between 2.5 and 5 R ⋆ across all of our observations. There is also significant variability in all emission lines studied, particularly Hα, Hβ, and Hγ. Using previously established relationships between line luminosity and accretion, we find that, on average, most lines reproduce accretion rates consistent with accretion shock modeling of HST spectra to within 0.5 dex. Looking at individual contemporaneous observations, however, these relationships are less accurate, suggesting that variability trends differ from the trends of the population and that these empirical relationships should be used with caution in studies of variability. * Based on observations collected at the European Southern Observatory under ESO program 106.20Z8.

Keywords: T Tauri stars, Stellar accretion
Afterglows from Binary Neutron Star Postmerger Systems Embedded in Active Galactic Nuclei Disks. The observability of afterglows from binary neutron star mergers occurring within active galactic nuclei (AGN) disks is investigated. We perform 3D GRMHD simulations of a postmerger system and follow the jet launched from the compact object. We use semianalytic techniques to study the propagation of the blast wave powered by the jet through an AGN disk-like external environment, extending to distances beyond the disk scale height. The synchrotron emission produced by the jet-driven forward shock is calculated to obtain the afterglow emission. The observability of this emission at different frequencies is assessed by comparing it to the quiescent AGN emission. In the scenarios where the afterglow could temporarily outshine the AGN, we find that detection will be more feasible at higher frequencies (≳1014 Hz) and the electromagnetic counterpart could manifest as a fast variability in the AGN emission, on timescales less than a day.

Keywords: Transient sources, Relativistic jets, Radiative transfer, High energy astrophysics
Modeling the Far-infrared Polarization Spectrum of a High-mass Star-forming Cloud. The polarization spectrum, or wavelength dependence of the polarization fraction, of interstellar dust emission provides important insights into the grain alignment mechanism of interstellar dust grains. We investigate the far-infrared polarization spectrum of a realistic simulated high-mass star-forming cloud under various models of grain alignment and emission. We find that neither a homogeneous grain alignment model nor a grain alignment model that includes collisional dealignment is able to produce the falling spectrum seen in observations. On the other hand, we find that a grain alignment model with grain alignment efficiency dependent on local temperature is capable of producing a falling spectrum that is in qualitative agreement with observations of OMC-1. For the model most in agreement with OMC-1, we find no correlation between the temperature and the slope of the polarization spectrum. However, we do find a positive correlation between the column density and the slope of the polarization spectrum. We suggest this latter correlation to be the result of wavelength-dependent polarization by absorption.

Keywords: Interstellar dust, Molecular clouds, Interstellar magnetic fields, Polarimetry, Magnetohydrodynamical simulations
ϵ Sagittarii: An Extreme Rapid Rotator with a Decretion Disk. We report high-precision, multiwavelength linear-polarization observations of the bright B9 (or A0) star ϵ Sagittarii. The polarization shows the distinctive wavelength dependence expected for a rapidly rotating star. Analysis of the polarization data reveals an angular rotation rate ω (=Ω/Ωcrit) of 0.995 or greater, the highest yet measured for a star in our Galaxy. An additional wavelength-independent polarization component is attributed to electron scattering in a low-density, edge-on gas disk that also produces the narrow absorption components seen in the spectrum. Several properties of the star (polarization due to a disk, occasional weak Hα emission, and multiple periodicities seen in space photometry) resemble those of Be stars, but the level of activity in all cases is much lower than that of typical Be stars. The stellar properties are inconsistent with single-rotating-star evolutionary tracks, indicating that it is most likely a product of binary interaction. The star is an excellent candidate for observation by interferometry, optical spectropolarimetry to detect the Öhman effect, and ultraviolet polarimetry, any of which would allow its extreme rotation to be tested and its stellar properties to be refined.

Keywords: Stellar rotation, Polarimetry, Circumstellar disks
Should Zeros Count? Modeling the Galaxy–Globular Cluster Scaling Relation with(out) Zero-inflated Count Models. The scaling relation between the size of a galaxy's globular cluster (GC) population (N GC) and the galaxy's stellar mass (M *) is usually described with a continuous, linear model, but in reality it is a count relationship that should be modeled as such. For massive galaxies, a negative binomial (NB) model has been shown to describe the data well, but it is unclear how the scaling relation behaves at low galaxy masses where a substantial portion of galaxies have N GC = 0. In this work, we test the utility of Poisson and NB models for describing the low-mass end of the N GC‑M * scaling relation. We introduce the use of zero-inflated versions of these models, which allow for larger zero populations (e.g., galaxies without GCs) than would otherwise be predicted. We evaluate our models with a variety of predictive model comparison methods, including predictive intervals, the leave-one-out cross-validation criterion, and posterior predictive comparisons. We find that the NB model is consistent with our data, but the naive Poisson is not. Moreover, we find that zero inflation of the models is not necessary to describe the population of low-mass galaxies that lack GCs, suggesting that a single formation and evolutionary process acts over all galaxy masses. Under the NB model, there does not appear to be anything unique about the lack of GCs in many low-mass galaxies; they are simply the low-mass extension of the larger N GC‑M * scaling relation.

Keywords: Globular star clusters, Bayesian statistics, Model selection, Astrostatistics techniques, Dwarf galaxies, Astrostatistics, Poisson distribution, Galaxy evolution, Galaxy processes
Velocity-resolved Ionization Mapping of Broad Line Region. I. Insights into Diverse Geometry and Kinematics. Broad emission lines of active galactic nuclei (AGNs) originate from the broad-line region (BLR), consisting of dense gas clouds in orbit around an accreting supermassive black hole. Understanding the geometry and kinematics of this region is crucial for gaining insights into the physics and evolution of AGNs. Conventional velocity-resolved reverberation mapping may face challenges in disentangling the degeneracy between intricate motion and geometry of this region. To address this challenge, new key constraints are required. Here, we report the discovery of an asymmetric BLR using a novel technique: velocity-resolved ionization mapping, which can map the distance of emitting gas clouds by measuring Hydrogen line ratios at different velocities. By analyzing spectroscopic monitoring data, we find that the Balmer decrement is anticorrelated with the continuum and correlated with the lags across broad emission line velocities. Some line ratio profiles deviate from the expectations for a symmetrically virialized BLR, suggesting that the redshifted and blueshifted gas clouds may not be equidistant from the supermassive black hole (SMBH). This asymmetric geometry might represent a formation imprint, provide new perspectives on the evolution of AGNs, and influence SMBH mass measurements.

Keywords: Supermassive black holes, Photoionization, Reverberation mapping, Active galactic nuclei, Time domain astronomy
Investigating the Mass of the Black Hole and Possible Wind Outflow of the Accretion Disk in the Tidal Disruption Event AT2021ehb. Tidal disruption events (TDEs) can potentially probe low-mass black holes (BHs) in host galaxies that might not adhere to bulge or stellar-dispersion relationships. At least initially, TDEs can also reveal super-Eddington accretion. X-ray spectroscopy can potentially constrain BH masses, and reveal ionized outflows associated with super-Eddington accretion. Our analysis of XMM-Newton X-ray observations of the TDE AT2021ehb, around 300 days post-disruption, reveals a soft spectrum and can be fit with a combination of multicolor disk blackbody and power-law components. Using two independent disk models with properties suited to TDEs, we estimate a BH mass at M ≃ 105.5 M ⊙, indicating AT2021ehb may expose the elusive low-mass end of the nuclear BH population. These models offer simple yet robust characterization; more complicated models are not required, but provide important context and caveats in the limit of moderately sensitive data. If disk reflection is included, the disk flux is lower and inferred BH masses are ∼0.35 dex higher. Simple wind formulations imply an extremely fast v out = −0.2c outflow and obviate a disk continuum component. Assuming a unity filling factor, such a wind implies an instantaneous mass outflow rate of  Ṁ≃5M⊙yr−1 . Such a high rate suggests that the filling factor for the ultrafast outflow (UFO) must be extremely low, and/or the UFO phase is ephemeral. We discuss the strengths and limitations of our analysis and avenues for future observations of TDEs.

Keywords: Accretion, X-ray astronomy, Black holes, High energy astrophysics, Tidal disruption, X-ray transient sources, Time domain astronomy
Global Effect of New Active Regions on Coronal Holes and Their Wind Streams. Solar wind prediction algorithms and simulations of coronal events often employ photospheric field maps that are assembled over a 27 day solar rotation. This has stimulated efforts to update and better synchronize the maps by applying flux transport and including observations of the back side of the Sun. Here, using potential-field source-surface extrapolations, we address the question of how the emergence of a large active region (AR) on the Sun's farside affects the coronal field and configuration of coronal holes on the Earth-facing side. We find that, if the new AR is located ∼135°–180° in longitude from Earth, the effect on the coronal field and solar wind near the central meridian will be almost negligible. This is because, when sunspot activity is relatively low, the outermost AR loops will become connected to the nearby polar fields; when sunspot activity is high, the newly emerged flux will connect to neighboring ARs. However, large ARs that emerge near the solar limb may sometimes have a significant effect on the field near the central meridian. In particular, a coronal hole having opposite polarity to that of the nearest sector of the AR may partially close down, resulting in slower wind; conversely, if the coronal hole has the same polarity as the facing AR sector, it will tend to increase in areal size, resulting in faster wind. In most cases, the main effect of a new AR will be to redistribute open flux between itself and neighboring coronal holes (including the polar holes) through interchange reconnection.

Keywords: Solar coronal holes, Solar active regions, Solar wind, Solar magnetic fields
From Halos to Galaxies. IX. Estimate of Halo Assembly History for SDSS Galaxy Groups. The properties of the galaxies are tightly connected to their host halo mass and halo assembly history. Accurate measurement of the halo assembly history in observation is challenging but crucial to the understanding of galaxy formation and evolution. The stellar-to-halo mass ratio (M */M h) for the centrals has often been used to indicate the halo assembly time t h,50 of the group, where t h,50 is the lookback time at which a halo has assembled half of its present-day virial mass. Using mock data from the semi-analytic models, we find that M */M h shows a significant scatter with t h,50, with a strong systematic difference between the group with a star-forming central (blue group) and passive central (red group). To improve the accuracy, we develop machine learning models to estimate t h,50 for galaxy groups using only observable quantities in the mocks. Since star formation quenching will decouple the co-growth of the dark matter and baryon, we train our models separately for blue and red groups. Our models have successfully recovered t h,50, within an accuracy of ∼1.09 Gyr. With careful calibrations of individual observable quantities in the mocks with Sloan Digital Sky Survey (SDSS) observations, we apply the trained models to the SDSS Yang et al. groups and derive the t h,50 for each group for the first time. The derived SDSS t h,50 distributions are in good agreement with that in the mocks, in particular for blue groups. The derived halo assembly history, together with the halo mass, make an important step forward in studying the halo–galaxy connections in observation.

Keywords: Galaxy dark matter halos, Galaxy evolution
X-Ray Variability in the Symbiotic Binary RT Cru: Principal Component Analysis. Hard X-ray-emitting (δ-type) symbiotic binaries, which exhibit a strong hard X-ray excess, have posed a challenge to our understanding of accretion physics in degenerate dwarfs. RT Cru, which is a member of the δ-type symbiotics, shows stochastic X-ray variability. Timing analyses of X-ray observations from XMM-Newton and NuSTAR, which we consider here, indicate hourly fluctuations, in addition to a spectral transition from 2007 to a harder state in 2012 seen with Suzaku observations. To trace the nature of X-ray variability, we analyze the multimission X-ray data using principal component analysis (PCA), which determines the spectral components that contribute most to the flickering behavior and the hardness transition. The Chandra HRC-S/LETG and XMM-Newton EPIC-pn data provide the primary PCA components, which may contain some variable emission features, especially in the soft excess. Additionally, the absorbing column (first order with 50%), along with the source continuum (20%), and a third component (9%)—which likely accounts for thermal emission in the soft band—are the three principal components found in the Suzaku XIS1 observations. The PCA components of the NuSTAR data also correspond to the continuum and possibly emission features. Our findings suggest that the spectral hardness transition between the two Suzaku observations is mainly due to changes in the absorbing material and X-ray continuum, while some changes in the thermal plasma emission may result in flickering-type variations.

Keywords: Principal component analysis, X-ray sources, Stellar accretion, Symbiotic binary stars, Time series analysis
Magnetic Eruption from a Three-ribbon Flare. We present observations and analysis of an eruptive M1.5 flare (SOL2014-08-01T18:13) in NOAA active region (AR) 12127, characterized by three flare ribbons, a confined filament between ribbons, and rotating sunspot motions as observed by the Solar Dynamics Observatory. The potential field extrapolation model shows a magnetic topology involving two intersecting quasi-separatrix layers (QSLs) forming a hyperbolic flux tube (HFT), which constitutes the fishbone structure for the three-ribbon flare. Two of the three ribbons show separation from each other, and the third ribbon is rather stationary at the QSL footpoints. The nonlinear force-free field extrapolation model implies the presence of a magnetic flux rope (MFR) structure between the two separating ribbons, which was unclear in the observation. This suggests that the standard reconnection scenario for eruptive flares applies to the two ribbons, and the QSL reconnection for the third ribbon. We find rotational flows around the sunspot, which may have caused the eruption by weakening the downward magnetic tension of the MFR. The confined filament is located in the region of relatively strong strapping field. The HFT topology and the accumulation of reconnected magnetic flux in the HFT may play a role in holding it from eruption. This eruption scenario differs from the one typically known for circular ribbon flares, which is mainly driven by a successful inside-out eruption of filaments. Our results demonstrate the diversity of solar magnetic eruption paths that arises from the complexity of the magnetic configuration.

Keywords: Solar flares, Solar filaments, Solar magnetic fields
Ongoing and Fossil Large-scale Outflows Detected in a High-redshift Radio Galaxy: [C II] Observations of TN J0924-2201 at z = 5.174. We present Atacama Large Millimeter/submillimeter Array observations of the [C II] 158 μm line and the underlying continuum emission of TN J0924‑2201, which is one of the most distant known radio galaxies at z &gt; 5. The [C II] line and 1 mm continuum emission are detected at the host galaxy. The systemic redshift derived from the [C II] line is z [C II] = 5.1736 ± 0.0002, indicating that the Lyα line is redshifted by a velocity of 1035 ± 10 km s‑1, marking the largest velocity offset between the [C II] and Lyα lines recorded at z &gt; 5 to date. In the central region of the host galaxy, we identify a redshifted substructure of [C II] with a velocity of 702 ± 17 km s‑1, which is close to the C IV line with a velocity of 500 ± 10 km s‑1. The position and the velocity offsets align with a model of an outflowing shell structure, consistent with the large velocity offset of Lyα. The nondetection of [C II] and dust emission from the three CO(1–0)-detected companions indicates their different nature compared to dwarf galaxies, based on the photodissociation region model. Given their large velocity of ∼1500 km s‑1, outflowing molecular clouds induced by the active galactic nucleus are the most plausible interpretation, and they may exceed the escape velocity of a 1013 M ⊙ halo. These results suggest that TN J0924‑2201, with ongoing and fossil large-scale outflows, is in a distinctive phase of removing molecular gas from a central massive galaxy in an overdense region in the early Universe. A dusty H I absorber at the host galaxy is an alternative interpretation.

Keywords: Radio active galactic nuclei, Radio galaxies, High-redshift galaxies, AGN host galaxies
The Three-phase Evolution of the Milky Way. We illustrate the formation and evolution of the Milky Way over cosmic time, utilizing a sample of 10 million red giant stars with full chemodynamical information, including metallicities and α-abundances from low-resolution Gaia XP spectra. The evolution of angular momentum as a function of metallicity—a rough proxy for stellar age, particularly for high-[α/Fe] stars—displays three distinct phases: the disordered and chaotic protogalaxy, the kinematically hot old disk, and the kinematically cold young disk. The old high-α disk starts at [Fe/H] ≈ ‑1.0, "spinning up" from the nascent protogalaxy, and then exhibiting a smooth "cooldown" toward more ordered and circular orbits at higher metallicities. The young low-α disk is kinematically cold throughout its metallicity range, with its observed properties modulated by a strong radial gradient. We interpret these trends using Milky Way analogs from the TNG50 cosmological simulation, identifying one that closely matches the kinematic evolution of our galaxy. This halo's protogalaxy spins up into a relatively thin and misaligned high-α disk at early times, which is subsequently heated and torqued by a major gas-rich merger. The merger contributes a large amount of low-metallicity gas and angular momentum, from which the kinematically cold low-α stellar disk is subsequently born. This simulated history parallels several observed features of the Milky Way, particularly the decisive Gaia–Sausage–Enceladus merger that likely occurred at z ≈ 2. Our results provide an all-sky perspective on the emerging picture of our galaxy's three-phase formation, impelled by the three physical mechanisms of spinup, merger, and cooldown.

Keywords: Milky Way formation, Milky Way dynamics, Milky Way disk, Milky Way evolution, Milky Way Galaxy
Theoretical Strong-line Metallicity Diagnostics for the JWST Era. The ratios of strong rest-frame optical emission lines are the dominant indicators of metallicities in high-redshift galaxies. Since typical strong-line-based metallicity indicators are calibrated on auroral lines at z = 0, their applicability for galaxies in the distant Universe is unclear. In this paper, we make use of mock emission-line data from cosmological simulations to investigate the calibration of rest-frame optical emission lines as metallicity indicators at high redshift. Our model, which couples the SIMBA cosmological galaxy formation simulation with CLOUDY photoionization calculations, includes contributions from H II regions, post-asymptotic-giant-branch stars, and diffuse ionized gas (DIG). We find mild redshift evolution in the 12 indicators that we study, which implies that the dominant physical properties that evolve in our simulations do have a discernible impact on the metallicity calibrations at high redshifts. When comparing our calibrations with high-redshift auroral line observations from the James Webb Space Telescope, we find a slight offset between our model results and the observations and find that a higher ionization parameter at high redshifts can be one of the possible explanations. We explore the physics that drives the shapes of strong-line metallicity relationships and propose calibrations for hitherto unexplored low-metallicity regimes. Finally, we study the contribution of DIG to total line fluxes. We find that the contribution of DIG increases with metallicity at z ∼ 0 for singly ionized oxygen and sulfur lines and can be as high as 70%, making it crucial to include their contribution when modeling nebular emission.

Keywords: Hydrodynamical simulations, Metallicity, H II regions, Galaxy evolution, High-redshift galaxies