Sazuna/UAT_keywords huggingface dataset:
Discovery of a Debris Disk around TWA 20. We report the discovery of a debris disk surrounding the M3 star TWA 20, revealed by JWST coronagraphic observations using the Near Infrared Camera. With reference differential imaging (RDI), we resolve the disk in scattered light in the F200W filter at a high signal-to-noise ratio and in the F444W filter at a low signal-to-noise ratio. The disk morphology and orientation are characterized via a forward-modeling approach, where we determine a radius of 64.7 −6.5+6.2  au and an inclination of 70.1 −3.3+2.5  degrees. Utilizing our forward model, we improve the fidelity of the debris disk image using model-constrained RDI. The newly discovered disk is one of only six disks detected in scattered light that orbit M dwarf stars; it is the third largest of the six resolved M dwarf disks and orbits the third faintest host star. The detection of this disk exemplifies the sensitivity of JWST to debris disks around low-luminosity host stars, which have historically been difficult to detect because these disks are cool and dim. We identify a nebulous structure that cannot be explained by an axisymmetric disk. A search for companions in the TWA 20 system yields no candidates.

Keywords: M dwarf stars, Exoplanets, Star forming regions, Exoplanet astronomy, Coronagraphic imaging, James Webb Space Telescope, Direct imaging, Circumstellar disks, Exoplanet detection methods, Exoplanet formation, Debris disks, Near infrared astronomy
Comprehensive JWST+ALMA Study on the Extended Lyα Emitters, Himiko, and CR7 at z ∼ 7: Blue Major Merger Systems in Stark Contrast to Submillimeter Galaxies. We present various properties of two bright extended Lyα objects, Himiko and COSMOS Redshift 7 (CR7), at z = 6.6 thoroughly investigated with JWST/NIRCam photometry, NIRSpec-Integral Field Unit spectroscopy, and Atacama Large Millimeter/submillimeter Array data, uncovering their physical origins. Himiko (CR7) shows at least five (four) clumps with small separations of 2.4─7.3 kpc and velocity offsets of ∆v &lt; 220 km s−1 in the [O III]λλ4959, 5007 line maps, three of which exhibit stellar components with comparable stellar masses ranging in  log(M*/M⊙)=8.4 ─9.0 (8.3─8.8), indicative of major merger systems that are consistent with our numerical simulations. The [C II] 158 μm and Lyα lines are found in the middle of two clumps (the brightest clump) in Himiko (CR7), suggesting that the distribution of neutral gas does not always coincide with that of ionized gas or stars in merging processes. We find that some of the clumps have broad [O III] components (250─400 km s−1) in Himiko and CR7, likely tracing outflow and tidal features, while the central clump in Himiko presents a broad Hα (∼1000 km s−1) line explained by an active galactic nucleus with a low-mass black hole of MBH = 106.6M⊙, which contribute to the extended and bright nature of Himiko and CR7. We find low metallicities of  12+log(O/H)= 7.9─8.1 in Himiko and CR7 based on auroral [O III]λ4363 and strong lines that are consistent with no 1 mm continuum detection corresponding to the dust-mass limits of Mdust ≲ 9 × 106M⊙. Himiko and CR7 are metal- and dust-poor blue merger systems with stellar and dust masses ≳2 orders of magnitude smaller than the massive dust-rich merger systems represented by submillimeter galaxies.

Keywords: Galaxy formation, High-redshift galaxies, Galaxy evolution
Molecular Gas and Star Formation in Dwarf Galaxies Observed by the Atacama Large Millimeter/submillimeter Array. We present a spatially resolved analysis of the molecular star formation law (SFL) and gravitational instability in a sample of nearby dwarf galaxies (NGC 1035, NGC 4310, NGC 4451, NGC 4701, NGC 5692, and NGC 6106), using high-resolution 12CO (J = 1 → 0) data from the Atacama Large Millimeter/submillimeter Array. We estimate the star formation rate (SFR) by combining the Galaxy Evolution Explorer near-ultraviolet and the Wide-field Infrared Survey Explorer 12 μm imaging data to examine the relationship between molecular gas and SFR densities on scales of several hundred parsecs. We find that the power-law slope of the molecular SFL ranges from 0.62 to 1.08, with an average value of N = 0.81 ± 0.18, increasing to N = 0.87 ± 0.05 when excluding galaxies with poorly constrained CO data. These results are roughly consistent with values observed in massive spiral galaxies, suggesting a universal molecular SFL when analyzed with sufficient resolution and sensitivity. Radial profiles of the Toomre Q parameter remain close to unity across the disks, with minimal radial variation, consistent with a self-regulated star formation model. Our results suggest that, despite their lower mass and metallicity, star formation in dwarf galaxies is governed by the same fundamental physical processes as in larger systems. This highlights the significance of high-resolution molecular gas observations in low-mass galaxies.

Keywords: Galaxy dynamics, Dwarf galaxies, Star formation, Galaxy kinematics, Interstellar medium, Radio astronomy
Eclipsing Stellar Flare on the Demon Star Algol Binary System Observed during the MAXI─NICER Follow-up Campaign in 2018. Algol is a well-known eclipsing binary hosting an active and variable star that exhibits frequent stellar flares. Here, we report our preplanned and coordinated rapid X-ray follow-up observations of an eclipsing flare on Algol. The Monitor of All-sky X-ray Image detected a flare on Algol at 05:52 UT on 2018 July 4. Subsequently, we carried out a prompt X-ray monitoring with the Neutron star Interior Composition ExploreR starting at 19:45 UT on the same day, and the observation ended at 06:02 UT on 2018 July 6. During the decaying phase of the flare, we successfully detected a 5.8 hr long eclipse, corresponding to the secondary eclipse in which Algol A blocks the line of sight to Algol B. During the eclipse, the 2─10 keV X-ray flux is decreased to the 20% level from 1.9 × 10−10 to 4.5 × 10−11 erg cm−2 s−1. We found a configuration of the flare size and location to explain the X-ray observations; e.g., the flare occurred at the latitude 45°S of the Algol B surface with a flare height of 1.9 × 1011 cm, corresponding to 0.8 times the stellar radius of Algol B, giving 80% obscuration of the flare loop by Algol A. The apparent absorption increase before the eclipse might originate from coronal mass ejection in the line of sight ejected during the flare.

Keywords: X-ray astronomy, Algol variable stars, Stellar activity, Stellar astronomy, Stellar flares, Eclipsing binary stars
Discovery of a 459 Hz Burst Oscillation in XTE J1810−189 with NICER. We present a detailed temporal study of a type I X-ray burst from the neutron star low-mass X-ray binary (NS-LMXB) XTE J1810−189, observed on 2023 April 27 using the Neutron Star Interior Composition Explorer. The burst exhibited a rapid rise time of 2.55 s, followed by an exponential decay lasting for 7.5 s, with a total duration of ∼13 s. Type I X-ray bursts are driven by thermonuclear burning on the surface of a neutron star in an NS-LMXB. As these bursts originate from the stellar surface they can exhibit highly coherent signals known as burst oscillations, which serve as probes of the neutron star's spin frequency. We report the detection of a burst oscillation signal at ∼459 Hz at the cooling tail of the burst. The oscillation showed a strong Leahy-normalized power of PL = 35.95 at 458.92 Hz, corresponding to a single-trial significance of 5.53σ and a multiple-trial corrected significance of 3.14σ. The folded pulse profile in the 0.2─12 keV band is well described by a constant plus sinusoid with a fractional rms amplitude of 14.63%. These results suggest that the burst oscillation frequency of XTE J1810-189 directly reflects on the neutron star's spin, measured here to be ∼2.18 ms, placing it among the rapidly rotating NS-LMXBs. This burst oscillation signal at the cooling tail of the burst can be interpreted through surface mode model or the asymmetric cooling wake model.

Keywords: Low-mass x-ray binary stars, Neutron stars, X-ray bursts, High energy astrophysics
High-energy Gamma Rays and Neutrinos from the Sun, Jupiter, and Earth. Cosmic rays (CRs) reaching the atmosphere of an astrophysical object produce showers of secondary particles that may then escape into space. Here we obtain the flux of gamma rays and neutrinos of energy E &gt; 10 GeV emitted by the Sun, Jupiter, and Earth. We show that while the solar magnetic field induces a flux of gamma rays from all the points on the Sun's surface, the dipolar magnetic field in the planets implies high-energy photons only from the very peripheral region. Neutrinos, in contrast, can cross these objects and emerge from any point on their surface. The emission from these astrophysical objects exceeds the diffuse flux from CR interactions with the interstellar medium and has a distinct spectrum and gamma-ray-to-neutrino ratio.

Keywords: Neutrino astronomy, Solar particle emission, Gamma-rays, Cosmic rays
The Origin of the Mg-rich Supernova Remnant J0550─6823 and the Frequency of Similar Events in the Large Magellanic Cloud. Shell burning and internal mixing in massive stars play an important role in setting the initial conditions for core-collapse supernova explosions. In the late stages of stellar evolution, intense shell burning can cause distinct convective regions to merge, fundamentally restructuring the stellar interior. Although such phenomena are difficult to observe directly, the observation of "Mg-rich" supernova remnants (SNRs) has recently emerged as a potential signature of these events. In this study, we reanalyze X-ray observations of J0550─6823, a SNR in the Large Magellanic Cloud (LMC) and a new candidate Mg-rich SNR. Our spectral analysis confirms a low Ne/Mg mass ratio of ≍1 and its classification as Mg-rich. By comparing the observational results with presupernova models, we suggest that the progenitor of J0550−6823 likely had an extended convective shell that reduces the Ne/Mg ratio prior to its explosion. Furthermore, we observe that ∼2─3 Mg-rich SNRs exist in the LMC, suggesting that ≲10%─40% of massive stars in the LMC may have had an extended convective shell, similar to what we observed in J0550−6823. This fraction would be important for understanding the final stages of the evolution of massive stars and Galactic chemical evolution.

Keywords: X-ray astronomy, Massive stars, Stellar structures, Supernova remnants
The Enhancement of Ion Heating in Kinetic, Antiparallel Reconnection in the Presence of a Flow Shear. We investigate the kinetic effects of upstream, magnetic field-aligned flow shear on antiparallel magnetic reconnection using 2.5D particle-in-cell simulations. Our results demonstrate that flow shear significantly alters the reconnection process, leading to enhanced ion heating, reduced outflow speeds, and a modified reconnection geometry. In contrast to previous Hall magnetohydrodynamic studies, we find that reconnection becomes a more efficient plasma heating mechanism in the presence of sub-Alfvénic flow shear, with ion heating increasing by as much as 300%. This enhanced heating is achieved by efficiently converting the incoming flow shear energy into thermal energy through isotropization in the exhaust. The enhanced heating leads to a pressure gradient away form the x-line exerting a force that reduces the outflow jet speed and slows down the reconnection process. This conversion is due to beam selection effects, mixing, and scattering in the exhaust. A theoretical model is developed that predicts well the exhaust heating and outflow speed reduction. These results offer a potential explanation for recent Parker Solar Probe observations of suppressed reconnection in the presence of flow shear and carry significant implications for energy dissipation in turbulent plasmas.

Keywords: Space plasmas, Plasma astrophysics, Solar magnetic reconnection
Supermassive Black Hole and Broad-line Region in NGC 5548: 2023 Reverberation Mapping Results. We present the results of the 2023 spectroscopic reverberation mapping campaign for active galactic nuclei (AGNs) of NGC 5548, continuing our long-term monitoring program. Using the Lijiang 2.4 m telescope, we obtained 74 spectra with a median cadence of 1.9 days. Through detailed spectral decomposition, we measured the light curves of the optical continuum at 5100 Å and the broad He II, He I, Hγ, and Hβ emission lines. The time lags of these lines relative to the continuum are measured as  1.3−0.6+1.6 ,  2.3−2.1+1.5 ,  10.0−1.8+2.0 , and  15.6−2.9+2.6  days (rest frame), respectively. Velocity-resolved lag profiles for Hγ and Hβ were constructed. Combined with data from previous seasons (2015─2021), we found the following: the radial ionization stratification of the broad-line region (BLR) is stable; the average virial mass of the supermassive black hole in NGC 5548 is (2.6 ± 1.1) × 108M⊙, consistent with the MBH─σ* relation; broad He II line exhibits the largest responsivity, followed by broad He I (or Hγ) and Hβ lines; and the BLR kinematics show significant temporal evolution, transitioning from virialized motions to signatures of inflow and outflow. Furthermore, an analysis of 35 yr of historical data confirms a 3.5 yr time lag between variations in the optical luminosity and the BLR radius, potentially implicating the role of radiation pressure or dynamical structure changes in the inner accretion disk. Long-term campaign demonstrates that the BLR in NGC 5548 is a robust yet dynamically evolving entity, providing crucial insights into AGN structure and accretion physics.

Keywords: Reverberation mapping, Active galactic nuclei, Time domain astronomy
Linking Magnetic Field Diagnostics with 3D Coronal Mass Ejection Speeds in Solar Active Regions. Understanding how active-region properties influence coronal mass ejection (CME) dynamics is essential for constraining eruption models and improving space-weather prediction. Magnetic diagnostics derived above polarity inversion lines (PILs), including the critical height (hcrit) of torus instability onset, the overlying field strength (Bt), and ribbon flux (Rf), provide physically motivated measures of eruption onset. The two main aims of this work are to (i) show that hcrit and Bt can equally well predict CME speeds when evaluated over the region of interest (ROI) not directly above the PIL, and (ii) assess the value of hcrit, Bt, and Rf in predicting CME speed. Photospheric magnetograms are modeled with potential-field extrapolations to obtain decay index profiles. Critical heights above PILs correlate strongly with 3D CME speed (r = 0.71). Using ROIs of ≍1.8, 3.7, and 7.3 Mm, centered on the PIL, weighted hcrit from the 7.3 × 7.3 ROI provides the strongest correlation (r = 0.73), while mean Bt at 150 Mm is weaker (r = 0.33). Combining both offers little improvement (r = 0.74), confirming hcrit as the dominant predictor. CME speed correlates moderately with Bt × Rf (r = 0.44), and highest when combined with hcrit (r = 0.76). Thus, in potential field models, ROI-based critical heights are as predictive as those above the PIL, indicating that the broader active-region field structure is equally valid as a diagnostic. When all parameters are considered together, hcrit alone consistently shows the highest predictive power for CME speed.

Keywords: Solar active region magnetic fields, Magnetohydrodynamics, Space weather, Solar coronal mass ejections, Solar corona
Probing Proton versus Electron Heating and Energization during Magnetic Reconnection. The mechanisms controlling the relative heating and energization of electrons and protons during magnetic reconnection are explored. Simulations are carried out with the kglobal model, which produces bulk heating and the extended power-law distributions of both species that have been documented in observations. The simulations have been carried out with a range of proton-to-electron mass ratios and upstream temperatures to isolate the factors that control energy gain. The simulations reveal that when the upstream temperatures of the two species are equal, the proton heating and energization exceed that of electrons, and that this is a consequence of the much larger energy gain of protons on their first entry into the reconnection exhaust. The effective energy gain of protons on exhaust entry scales as  miCA2  since the protons counterstream at the Alfvén speed CA while the initial electron energy gain is smaller by the factor  (βe0me/mi)1/2 . Since Fermi reflection during flux rope merger dominates energy gain in large-scale reconnecting systems and the rate of energy gain is proportional to energy, protons continue to gain energy faster than electrons for the duration of the simulations, leading to temperature increments of protons exceeding that of electrons, and the nonthermal energy content of protons also exceeding that of electrons.

Keywords: Magnetic fields, Solar magnetic reconnection, Plasma physics
Active Dwarf Galaxy Database. II. Connections between Host Galaxy Properties and Black Hole Accretion Signatures. We investigate the connection between accretion signatures and host galaxy properties in the context of how active dwarf galaxies are identified. We use the database constructed in E. J. Wasleske &amp; V. F. Baldassare, which contains dwarf galaxies that were selected as active galaxies by optical spectroscopy, infrared colors, X-ray brightness, and photometric variability. Multiwavelength archival data were used to consistently apply all of these methods to every galaxy within this compiled set. The cross-application of these methods resulted in a diversity of subpopulations identified as active by some set of these techniques. In this paper, we estimate host galaxy properties from spectral energy distribution models. We connect the active galactic nucleus (AGN) signatures to our estimated host galaxies' properties using statistical dimensionality reduction methods. We find that dwarf AGN selected by infrared colors are the most distinct population, with the highest star formation rates and lowest stellar masses. We also find some other key population differences, such as the broad-line AGN having significantly higher AGN luminosities. X-ray- and variability-selected AGN have higher average star formation rates than those selected with optical narrow-line spectroscopic diagrams. Our connections to the host galaxy parameters potentially point to the subpopulations representing different epochs of the evolution of accretion.

Keywords: Active galaxies, Dwarf galaxies, Active galactic nuclei, Spectral energy distribution, Astrophysical black holes
The First LWA Swarm Calibrator Survey. The LWA Swarm is an aperture synthesis telescope consisting of interconnected Long Wavelength Array (LWA) stations autonomously making joint observations. In 2024, the LWA collaboration completed commissioning for the LWA─North Arm, a 64-element "swarm" station, and construction is underway to build two additional LWA Swarm stations in Arizona and Texas. By early 2026, the LWA Swarm will be a six-station long baseline interferometer, capable of arcsecond resolution imaging with millijansky sensitivity. Here we use the three-element interferometer consisting of LWA1, LWA-SV, and LWA-NA to survey 30 radio sources as candidate calibrators for the LWA Swarm. Of these 30 sources observed we find 25 viable calibrators and present images of all sources at 66 MHz. Based on the properties of the observed calibrators, we conclude that many other suitable calibrators will be available to the LWA Swarm. In anticipation of the availability of this new instrument, we provide a preliminary guide to observing and calibrating LWA Swarm data.

Keywords: Calibration, Very long baseline interferometry, Radio sources
How Invisible Stellar Halos Bias Our Understanding of Ultrafaint Galaxies. We explore how a realistic surface brightness (SB) detection limit of μV ≍ 32.5 mag arcsec−2 for stars at the edges of ultrafaint galaxies affects our ability to infer their underlying properties. We use a sample of 19 galaxies with stellar masses ≍400─40,000 M⊙simulated with FIRE-2 physics and baryonic mass resolution of 30 M⊙. The SB cut leads to smaller sizes, lower stellar masses, and lower stellar velocity dispersions than the values inferred without the cut. However, by imposing this realistic limit, our inferred galaxy properties lie closer to observed populations in the mass-size plane, better match observed velocity dispersions as a function of stellar mass, and better reproduce derived circular velocities as a function of half-light radius. For the most massive galaxies in our sample, the SB cut leads to higher mean [Fe/H] values, but the increase is not enough to match the observed MZR. Finally, we demonstrate that the common J. Wolf et al. dynamical mass estimator is less accurate when the SB cut is applied. For our lowest-mass galaxies, in particular, excluding the low-surface brightness outskirts causes us to overestimate their central dark-matter densities and virial masses. This suggests that attempts to use mass estimates of ultrafaint galaxies to constrain dark-matter physics or to place constraints on the low-mass threshold of galaxy formation must take into account surface brightness limits or risk significant biases.

Keywords: Local Group, Stellar kinematics, Cold dark matter, Dwarf galaxies, Galaxy dynamics, Dark matter
Transition to Petschek Reconnection in Subrelativistic Pair Plasmas: Implications for Particle Acceleration. While relativistic magnetic reconnection in pair plasmas has emerged in recent years as a candidate for the origin of radiation from extreme astrophysical environments, the corresponding subrelativistic pair-plasma regime has remained less explored, leaving open the question of how relativistic physics affects reconnection. In this paper, we investigate the differences between these regimes by contrasting two-dimensional particle-in-cell simulations of reconnection in pair plasmas with relativistic magnetization (σ ≫ 1) and subrelativistic magnetization (σ &lt; 1). By utilizing unprecedentedly large domain sizes and outflow boundary conditions, we demonstrate that lowering the magnetization results in a change in the reconnection geometry from a plasmoid chain to a Petschek geometry, where laminar exhausts bounded by slow-mode shocks emanate from a single diffusion region. We attribute this change to the reduced plasmoid production rate in the low-σ case: When the secondary tearing rate is sufficiently low, plasmoids are too few in number to prevent the system from relaxing into a stable Petschek configuration. This geometric change also affects particle energization: We show that while high-σ plasmoid chains generate power-law energy spectra, low-σ Petschek exhausts merely heat incoming plasma and yield negligible nonthermal acceleration. These results have implications for predicting the global current sheet geometry and the resulting energy spectra in a variety of systems.

Keywords: Space plasmas, Plasma astrophysics, Plasma physics