Sazuna/UAT_keywords huggingface dataset:
Emission Characteristics of Energetic Electrons with Crescent-shaped Velocity Distributions. Solar flares release magnetic energy through reconnection, accelerating electrons into nonthermal velocity distributions, including crescent-shaped electron populations. These energetic electron distributions are crucial in driving instabilities that can lead to distinct electromagnetic emissions. This study investigates the emission properties of crescent-shaped electron velocity distribution functions under different frequency ratios (ωpe/Ωce), critical for understanding plasma conditions in various astrophysical environments, by comparing the emissions and intensities of waves among different cases. Here, we study and analyze three distinct frequency ratio conditions (2.2, 10, and 1, designated as cases A, B, and C, respectively). We find that the beam-Langmuir and upper-hybrid modes can be efficiently excited, leading to further plasma emissions in different cases. Our study reveals that the fundamental (O/F) emission can reach a maximum value of ∼10‑4Ek0, while the harmonics (H) can extend to ∼1.5 × 10‑5Ek0, depending on the frequency ratio of the environment. The intensity of the fundamental mode exceeds previous findings for pure-ring, pure-beam, and ring–beam distributions, highlighting the impact of crescent-shaped electron velocity distributions on wave excitation and emission processes. This effect is notably influenced by different frequency ratios, offering new insights into the way that nonthermal electron distributions affect the plasma emission process.

Keywords: Solar activity, Radio bursts, Solar coronal radio emission, Solar corona
PHANGS-ML: The Universal Relation between PAH Band and Optical Line Ratios across Nearby Star-forming Galaxies. The structure and chemistry of the dusty interstellar medium (ISM) are shaped by complex processes that depend on the local radiation field, gas composition, and dust grain properties. Of particular importance are polycyclic aromatic hydrocarbons (PAHs), which emit strong vibrational bands in the mid-infrared, and play a key role in the ISM energy balance. We recently identified global correlations between PAH band and optical line ratios across three nearby galaxies, suggesting a connection between PAH heating and gas ionization throughout the ISM. In this work, we perform a census of the PAH heating─gas ionization connection using ∼700,000 independent pixels that probe scales of 40─150 pc in 19 nearby star-forming galaxies from the PHANGS survey. We find a universal relation between  PAH(11.3 μm/7.7 μm) and  ([S II]/Hα) with a slope of ∼0.2 and a scatter of ∼0.025 dex. The only exception is a group of anomalous pixels that show unusually high (11.3 μm/7.7 μm) PAH ratios in regions with old stellar populations and high starlight-to-dust emission ratios. Their mid-infrared spectra resemble those of elliptical galaxies. Active galactic nucleus hosts show modestly steeper slopes, with a ∼10% increase in PAH(11.3 μm/7.7 μm) in the diffuse gas on kiloparsec scales. This universal relation implies an emerging simplicity in the complex ISM, with a sequence that is driven by a single varying property: the spectral shape of the interstellar radiation field. This suggests that other properties, such as gas-phase abundances, gas ionization parameter, and grain charge distribution, are relatively uniform in all but specific cases.

Keywords: Interstellar dust, Polycyclic aromatic hydrocarbons, Astrostatistics, Warm ionized medium, Interstellar medium
Unveiling the Cosmic Chemistry: Revisiting the Mass–Metallicity Relation with JWST/NIRSpec at 4 &lt; z &lt; 10. We present star formation rates (SFRs), the mass–metallicity relation (MZR), and the SFR-dependent MZR across redshifts 4–10 using 81 star-forming galaxies observed by the JWST NIRSpec employing both low-resolution PRISM and medium-resolution gratings, including galaxies from the JWST Advanced Deep Extragalactic Survey (JADES) GOODS-N and GOODS-S fields, the JWST-PRIMAL Legacy Survey, and additional galaxies from the literature in the A2744, SMACS-0723, RXJ2129, BDF, COSMOS, and MACS1149 fields. These galaxies span a 3 dex stellar mass range of 107 &lt; M */M ⊙ &lt; 1010, with an average SFR of 7.2 ± 1.2M ⊙ yr‑1 and an average metallicity of  . Our findings align with previous observations up to z = 8 for the MZR and indicate no deviation from the local Universe fundamental metallicity relation (FMR) up to this redshift. Beyond z = 8, we observe a significant deviation (∼0.27 dex) in FMR, consistent with recent JWST findings. We also integrate Cosmic Evolution Early Release Science (135 galaxies) and JADES (47 galaxies) samples with our data to study the metallicity evolution with redshift in a combined sample of 263 galaxies, revealing a decreasing metallicity trend with a slope of 0.067 ± 0.013, consistent with IllustrisTNG and EAGLE but contradicting the FIRE simulations. We introduce an empirical mass–metallicity–redshift relation:   × , which accurately reproduces the observed trends in metallicity with both redshift and stellar mass. This trend underscores the "Grand Challenge" in understanding the factors driving high-redshift galactic metallicity trends, such as inflow, outflow, and active galactic nucleus/stellar feedback—and emphasizes the need for further investigations with larger samples and enhanced simulations.

Keywords: James Webb Space Telescope
Automated Detection of Galactic Rings from Sloan Digital Sky Survey Images. Morphological features in galaxies—like spiral arms, bars, rings, and tidal tails, etc.—carry information about their structure, origin, and evolution. It is therefore important to catalog and study such features and to correlate them with other basic galaxy properties, the environments in which the galaxies are located, and their interactions with other galaxies. The volume of present and future data on galaxies is so large that traditional methods, which involve expert astronomers identifying morphological features through visual inspection, are no longer sufficient. It is therefore necessary to use AI-based techniques like machine learning and deep learning to find morphological structures quickly and efficiently. We report in this study the application of deep learning for finding ring-like structures in galaxy images from the Sloan Digital Sky Survey (SDSS) DR18. We use a catalog by R. J. Buta of ringed galaxies from SDSS to train the network, reaching good accuracy and recall, and generate a catalog of 29,420 galaxies, of which 4855 have ring-like structures with prediction confidence exceeding 90%. Using a catalog of barred galaxy images identified by S. Abraham et. al. with deep-learning techniques, we identify a set of 2087 galaxies with bars as well as rings. The catalog should be very useful in understanding the origin of these important morphological structures. As an example of the usefulness of the catalog, we explore the environments and star formation characteristics of the ring galaxies in our sample.

Keywords: Catalogs, Galaxies, Astronomy data analysis, Astronomy image processing
Radio Follow-up Observations of SN 2023ixf by Japanese and Korean Very Long Baseline Interferometers. We report on radio follow-up observations of the nearby Type II supernova SN 2023ixf, spanning from 1.7 to 269.9 days after the explosion, conducted using three very long baseline interferometers (VLBIs), which are the Japanese VLBI Network, the VLBI Exploration of Radio Astrometry, and the Korean VLBI Network. In three observation epochs (152.3, 206.1, and 269.9 days), we detected emission at the 6.9 and 8.4 GHz bands, with a flux density of ~5 mJy. The flux density reached a peak at around 206.1 days, which is longer than the timescale to reach the peak observed in typical Type II supernovae. Based on an analytical model of radio emission, our late-time detections were inferred to be due to decreasing optical depth. In this case, the mass-loss rate of the progenitor is estimated to have increased from ~10‑6–10‑5 M⊙ yr‑1 to ~10‑4 M⊙ yr‑1 between 28 and 6 yr before the explosion. Our radio constraints are also consistent with the mass-loss rate needed to produce a confined circumstellar medium proposed by previous studies, which suggest that the mass-loss rate increased from ~10‑4 M⊙ yr‑1 to ≳10‑2 M⊙ yr‑1 in the last few years before the explosion.

Keywords: Red supergiant stars, Core-collapse supernovae, Type II supernovae, Massive stars, Very long baseline interferometry, Stellar mass loss, Circumstellar matter, Supernovae, Stellar evolution
Orbit of a Possible Planet X. The plausibility of an unseen planet in the outer solar system, and the expected orbit and mass of such a planet, have long been a topic of inquiry and debate. We calculate the long-term orbital stability of distant trans-Neptunian objects (TNOs), which allows us to expand the sample of objects that would carry dynamical information about a hypothetical unseen planet in the solar system. Using this expanded sample, we find statistically significant clustering at the ∼3σ level for TNOs with semimajor axes &gt; 170 au in the longitude of perihelion (ϖ), but not in inclination (i), argument of perihelion (ω), or longitude of node (Ω). Since a natural explanation for clustering in ϖ is an unseen planet, we run 300 N-body simulations with the giant planets, a disk of test particles representing Kuiper Belt objects, and an additional planet with varied initial conditions for its mass, semimajor axis, eccentricity, and inclination. Based on the distribution of test particles after 1–2 Gyr, we compute relative likelihoods given the actual distribution of ϖ as a function of semimajor axis for distant TNOs on stable orbits using a significantly larger sample than previous work. We find the best-fit unseen planet parameters to have mass mp = 4.4 ± 1.1 M⊕, semimajor axis ap = 290 ± 30 au, eccentricity ep = 0.29 ± 0.13, and inclination ip = 6 .° 8 ± 5 .° 0. Only 0.06% of the M. E. Brown &amp; K. Batygin Planet Nine reference population produce probabilities within 1σ of the maximum within our quadrivariate model, indicating that our work identifies a distinct preferred region of parameter space for an unseen planet in the solar system.

Keywords: Solar system, Trans-Neptunian objects
Detection of a Magnetic Discontinuity in the Upper Solar Chromosphere Associated with a Coronal Loop Brightening Observed by CLASP2.1. We report the first detection of a magnetic discontinuity in the upper solar chromosphere associated with a coronal loop brightening. Our findings are based on novel observations obtained by the Chromospheric LAyer SpectroPolarimeter (CLASP2.1) suborbital space experiment. During its short 6 minute flight, CLASP2.1 successfully obtained spectropolarimetric data across the Mg II h and k lines, which allowed us to map the longitudinal magnetic field at multiple heights in the chromosphere of a solar active region. During our observation, we found a coronal loop brightening that was intermittently and recurrently heated. The temperature of the brightening plasma is above 2.5 MK, which is higher than the ambient temperature, and no corresponding brightening is detected in the images of the photosphere and lower chromosphere. The notable finding of our study is that the coronal loop brightening of interest is observed across a region where the magnetic field polarity changes abruptly in the upper chromosphere. Our results provide observational evidence that the heating mechanism of the coronal loop brightening is consistent with magnetic reconnection in the upper solar chromosphere.

Keywords: Solar magnetic reconnection, Solar coronal loops, Solar coronal heating, Solar magnetic fields, Solar chromosphere
Observed Steep and Shallow Spectra, Narrow and Broadband Spectra, Multifrequency Simultaneous Spectra, and Statistical Fringe Spectra in Fast Radio Bursts: Various Faces of Intrinsic Quasi-periodic Spectra?. Through analysis, modelings, and simulations, we show that if the spectra of fast radio bursts (FRBs) are intrinsically quasi-periodic, and likely produced by coherent curvature radiation from quasi-periodic structured bunches, then the observed steep and shallow spectra, narrow and broadband spectra, multifrequency simultaneous spectra, as well as possible statistical fringe spectra in FRBs, could all be various manifestations of them. If so, the period properties of the structured bunches, as inferred from the observed multifrequency simultaneous spectra and potential statistical fringe spectra, may provide valuable insights into the mechanisms behind the formation of such structured bunches.

Keywords: Spectral index, Radio bursts, Spectral energy distribution, Radio transient sources
Extreme Solar Particle Ejection Event in the Last Few Million Years from Asteroid Itokawa Sample. Unusual explosive activity occasionally occurs from the Sun, releasing large amounts of solar energetic particles. Extreme solar particle ejection events in the past 11,000 yr have been detected by sharp increases of cosmogenic isotopes in annual tree rings and ice cores. However, quantitative estimation of the event magnitudes is not straightforward, as the cosmogenic isotopes are indirect records of solar particles. Similar solar particle ejection events may also accumulate records in surface materials of airless bodies such as the Moon and asteroids. Samples from the asteroid 25143 Itokawa have been irradiated by solar winds for tens to hundreds of years at some points in the last few million years. Here, we report implantation profiles of solar particle He from an Itokawa regolith grain that trace an extreme solar particle ejection event. The implantation profiles indicate that the fluences of suprathermal solar particles were 250–1300 times larger than that expected from the current normal solar activity. Since the degrees of excesses are inversely related to the solar wind irradiation periods, the high-energy particle fluence would have been derived from a single event. The event was approximately 40 times larger than the 2003 Halloween solar storms, which is one of the largest solar particle ejection events observed since the space-based measurement of solar activity began. The event magnitude is similar to the largest events inferred from the cosmogenic isotope records in terrestrial samples. Our result provides direct evidence of an extreme solar particle ejection event in the last few million years.

Keywords: Mass spectrometry, Asteroids, Solar energetic particles, Solar wind, Solar storm, Regolith
Modeling Energetic Proton Transport from a Stream Interaction Region to Compound Streams. Energetic proton events associated with a stream interaction region (SIR) were observed by two Solar-Terrestrial Relations Observatory (STEREO) and WIND spacecraft from 2007 September 19 to September 25. Different from the measurements of STEREO-A and WIND, the observational data of STEREO-B show additional particle intensity increases when the spacecraft is immersed into the compound stream region with poor compression signatures after the passage of the SIR. In order to investigate this particular event, we simulated proton transport with a solar wind pattern obtained from the two-dimensional analytical model driven by plasma and magnetic field data of the spacecraft. We find that the additional energetic proton event is not an autonomous event created by the compound streams and is closely associated with the accelerated particles in the preceding SIR structure. We highlight the variation in particle distribution as a function of radial distance within the SIR. The magnetic field configuration in the compound stream region observed by STEREO-B provides a more direct connection to the source particle region, which presents a view to explain the differences between the energetic proton observations of the three spacecraft.

Keywords: Solar wind, Interplanetary particle acceleration, Corotating streams, Magnetic fields
A Catalog of Stellar and Dust Properties for 500,000 Stars in the Southwest Bar of the Small Magellanic Cloud. We present a catalog of individual stellar and dust extinction properties along close to 500,000 sight lines in the southwest bar of the Small Magellanic Cloud (SMC). The catalog is based on multiband Hubble Space Telescope photometric data spanning near-ultraviolet to near-infrared wavelengths from the Small Magellanic Cloud Investigation of Dust and Gas Evolution survey (SMIDGE) covering a 100 × 200 pc area. We use the probabilistic technique of the Bayesian Extinction And Stellar Tool (BEAST) to model the spectral energy distributions of individual stars in SMIDGE and include the effects of observational uncertainties in the data. We compare BEAST-derived dust extinction properties with tracers of the interstellar medium, such as the emission from the 12CO (2–1) transition (I(CO)), the dust mass surface density (Σdust) from far-IR emission, the H I column density (N(H I)) from the 21 cm transition, and the mass fraction of polycyclic aromatic hydrocarbons (PAHs; q PAH, derived from IR emission). We find that the dust extinction (A(V)) in the SMIDGE field is strongly correlated with Σdust and I(CO), and less so with N(H I) and q PAH, and suggest potential explanations. Our extinction measurements are also sensitive to the presence of the 2175 Å bump in the extinction curve toward UV bright stars. While most do not show evidence for the bump, we identify ∼200 lines of sight that are 2175 Å bump candidates. Furthermore, we find distinct structures in the dust extinction–distance distributions that provide insights into the 3D geometry of the SMC.

Keywords: Interstellar dust, Stellar properties, Dwarf galaxies, Small Magellanic Cloud, Galaxy structure, Interstellar dust extinction, Spectral energy distribution, Interstellar medium, Hertzsprung Russell diagram, Magellanic Clouds
Prospects for Observing High-redshift Radio-loud Quasars in the SKA Era: Paving the Way for 21 cm Forest Observations. The 21 cm forest is a sensitive probe for the early heating process and small-scale structures during the epoch of reionization (EOR), to be realized with the upcoming Square Kilometre Array (SKA). Its detection relies on the availability of radio-bright background sources, among which the radio-loud quasars are very promising, but their abundance during the EOR is still poorly constrained due to limited observations. In this work, we use a physics-driven model to forecast future radio-loud quasar observations. We fit the parameters of the model using observational data of high-redshift quasars. Assuming Eddington accretion, the model yields an average lifetime of tq ~ 105.5 yr for quasars at z ~ 6, consistent with recent results obtained from quasar proximity zone observation. We show that if the radio-loud fraction of quasars evolves with redshift, it will significantly reduce the abundance of observable radio-loud quasars in the SKA era, making 21 cm forest studies challenging. With a constant radio-loud fraction, our model suggests that a 1 yr sky survey conducted with SKA-LOW has the capability to detect approximately 20 radio-loud quasars at z ~ 9, with sufficient sensitivity to resolve individual 21 cm forest lines.

Keywords: Radio loud quasars, H I line emission, Reionization, Quasars
Can Alfvénic Fluctuations Affect the Correlation and Complexity of Magnetic Field of Magnetic Ejecta? A Case Study Based on Multi-spacecraft Measurements at 1 au. We investigate whether Alfvénic fluctuations (AFs) can affect the structure of magnetic ejecta (ME) within interplanetary coronal mass ejections (ICMEs). We study an ICME observed on 2001 December 29 at 1 au by the Advanced Composition Explorer (ACE) and Wind, at a total angular separation of ~0 8 (~ 0.014 au). We focus on the correlation and complexity of its magnetic structure measured between two spacecraft in association with large-amplitude AFs. The Alfvénicity of the ME is investigated in terms of the residual energy and cross helicity of fluctuations. We find that as for the event of interest, large-amplitude AFs occur in the rear region of the ME at both Wind and ACE with a duration of about 6 hr. We compare the correlation of the magnetic field strength and vector components measured between Wind and ACE, and investigate complexity in terms of the magnetic hodograms. The region showing AFs is found to be associated with a decreased correlation of the magnetic field components and an increased complexity of the ME magnetic configuration detected at ACE and Wind, which may be due to the fact that the two spacecraft crossing the same ME along different trajectories likely sampled AFs in different oscillation phases. Combining multipoint in situ measurements and remote-sensing observations of the ICME source region, we further discuss different potential sources of the AFs.

Keywords: Solar wind, Interplanetary magnetic fields, Solar coronal mass ejections
Latitude Quenching Nonlinearity in the Solar Dynamo. We compare two candidate nonlinearities for regulating the solar cycle within the Babcock–Leighton paradigm: tilt quenching (whereby the tilt of active regions is reduced in stronger cycles) and latitude quenching (whereby flux emerges at higher latitudes in stronger solar cycles). Digitized historical observations are used to build a database of individual magnetic plage regions from 1923 to 1985. The regions are selected by thresholding in Ca II K synoptic maps, with polarities constrained using Mount Wilson Observatory sunspot measurements. The resulting data show weak evidence for tilt quenching, but much stronger evidence for latitude quenching. Further, we use proxy observations of the polar field from faculae to construct a best-fit surface flux transport model driven by our database of emerging regions. A better fit is obtained when the sunspot measurements are used, compared to a reference model where all polarities are filled using Hale's Law. The optimization suggests clearly that the "dynamo effectivity range" of the Sun during this period should be less than 10°; this is also consistent with latitude quenching being dominant over tilt quenching.

Keywords: Solar cycle, Solar dynamo, Solar magnetic fields
Strongly Magnetized Accretion with Low Angular Momentum Produces a Weak Jet. We study the spherical accretion of magnetized plasma with low angular momentum onto a supermassive black hole, utilizing global general relativistic magnetohydrodynamic simulations. Black hole-driven feedback in the form of magnetic eruptions and jets triggers magnetized turbulence in the surrounding medium. We find that when the Bondi radius exceeds a certain value relative to the black hole's gravitational radius, this turbulence restricts the subsequent inflow of magnetic flux, strongly suppressing the strength of the jet. Consequently, magnetically arrested disks and powerful jets are not a generic outcome of the accretion of magnetized plasma, even if there is an abundance of magnetic flux available in the system. However, if there is significant angular momentum in the inflowing gas, the eruption-driven turbulence is suppressed (sheared out), allowing for the presence of a powerful jet. Both the initially rotating and nonrotating flows go through periods of low and high gas angular momentum, showing that the angular momentum content of the inflowing gas is not just a feature of the ambient medium, but is strongly modified by the eruption and jet-driven black hole feedback. In the lower-angular-momentum states, our results predict that there should be dynamically strong magnetic fields on horizon scales, but no powerful jet; this state may be consistent with Sgr A* in the Galactic center.

Keywords: Accretion, Supermassive black holes, Magnetohydrodynamics, Jets, Black holes, High energy astrophysics, Plasma astrophysics, Low-luminosity active galactic nuclei, Active galactic nuclei, Astrophysical black holes