Sazuna/UAT_keywords huggingface dataset:
Discovery of Metal-poor and Distant Pre–Main Sequence Candidates in WLM with JWST. We present the discovery of 12 metal-poor and distant pre–main sequence (PMS) candidates in the dwarf irregular galaxy Wolf–Lundmark–Melotte ∼968 kpc away, at a present-day metallicity of [Fe/H] ∼ –0.9. These candidates have masses between 1.25 and 5 M⊙, with ages &lt;10 Myr, and exhibit significant near-infrared excesses at 2.5 and 4.3 μm. They are concentrated within a cluster roughly 10 pc (2″) across, situated in the H II region [HM95]-9. These are the most distant and metal-poor PMS stars known, and they can offer new quantitative insights into star formation at low metallicities.

Keywords: Dwarf irregular galaxies, Star formation, Pre-main sequence
The Extraordinary Long-lasting Infrared Echo of PS16dtm Reveals an Extremely Energetic Nuclear Outburst. PS16dtm is one of the earliest reported tidal disruption events (TDEs) in active galactic nuclei and displays a remarkably bright and long-lived infrared (IR) echo revealed by multiepoch photometry from the Wide-field Infrared Survey Explorer (WISE). After a rapid rise in the first year, the echo remains persistently at a high state from 2017 July to 2024 July, the latest epoch, and keeps an almost constant color. We have fitted the extraordinary IR emission with a refined dust echo model by taking into account the dust sublimation process. The fitting suggests that an extremely giant dust structure with a new inner radius of ∼1.6 pc and an ultrahigh peak bolometric luminosity, i.e., ∼6 × 1046 erg s‑1 for typical 0.1 μm-sized silicate grain, is required to account for the IR echo. This work highlights the distinctive value of IR echoes in measuring the accurate intrinsic bolometric luminosity and thus the total radiated energy of TDEs, which could be severely underestimated by traditional methods, i.e., probably by more than 1 order of magnitude in PS16dtm. Such large energetic output compared to normal TDEs could be boosted by the preexisting accretion disk and gas clouds around the black hole. Our model can be validated in the near future by IR time-domain surveys such as the Near-Earth Object Surveyor, given the recent retirement of WISE. In addition, the potential for spatially resolving a receding dusty torus after a TDE could also be an exciting subject in the era of advanced IR interferometry.

Keywords: High energy astrophysics, Tidal disruption, Infrared astronomy, Active galactic nuclei, Time domain astronomy
Stellar Streams Reveal the Mass Loss of Globular Clusters. Globular cluster (GC) streams, debris of stars tidally stripped from their progenitor GCs, have densities that correlate positively with the GC mass-loss rate. In this work, we employ a novel particle spray algorithm that can accurately reproduce the morphology of streams of various orbital types, enabling us to uncover the relationship between the GC mass-loss history and stream density profiles. Using recent discoveries of GC streams from Gaia Data Release 3, we present, for the first time, a catalog of directly observed mass-loss rates for 12 Galactic GCs, ranging from 0.5 to 200 M⊙ Myr‑1. By fitting power-law relations between the mass-loss rate and key GC properties, we identify positive correlations with GC mass and orbital frequency, consistent with the predictions from N-body simulations.

Keywords: Globular star clusters, Galaxy dynamics, Stellar dynamics, Stellar streams
Exploring the Complex Heliotail Boundary by an Extended Level Set Approach. There is an ongoing debate regarding the shape of the heliotail. Studies have shown that the heliotail may be "comet-like," extending for thousands of au. Some previous works defined the heliopause using magnetohydrodynamic variables, which only serve as an approximation to capture the heliopause in all directions. Here we use a level set method in our heliospheric model to constrain the location of the heliopause. The level set function, fHP, is defined by boundary conditions, having a value of +1 at the inner boundary and ‑1 at the outer boundary. We find that the fHP = 0 criterion, the standard heliopause definition used by other models to determine where solar wind and interstellar plasma meet, is impacted in the heliotail, where there is a broad mixing region of solar wind and interstellar medium plasma, by the nature of turbulent flows in the heliotail. We explore a different isosurface, defined by fHP = 0.99, where the interface is composed of 99.5% solar wind and 0.50% interstellar medium. This determines the limits of the heliosphere by the region of solar wind flow that is minimally influenced by the interstellar flow. This region also contains magnetic field lines with at least one end anchored to the Sun. We obtain a split heliotail structure using the fHP = 0.99 criterion.

Keywords: Heliopause, Magnetohydrodynamics, Heliosphere, Solar wind, Computational methods, Interstellar medium, Heliosheath
Measurement of Turbulence Injection Scale Down to the Chromosphere. The solar atmosphere displays a sharp temperature gradient, starting from spicules in the chromosphere at 2 × 104 K, outward into the corona exceeding   K. Plasma turbulence produced by the transverse motion of magnetic fields anchored in the photosphere is likely the energy source producing this gradient. However, very little is known about the turbulent structures near the solar surface. Using the highest spatial resolution white-light total solar eclipse image to date, we measure the transverse correlation length at distances ranging from 0.33 to 94 Mm above the solar surface—2 orders of magnitude closer than previous estimates. Our results show that the turbulence injection scale in the chromosphere is ∼1.5 Mm, which we associate with the size of granules since they are the only structured features of comparable size. Further, the change in perpendicular correlation length with distance from the solar surface exhibits a plateau in the first 4 Mm, followed by a rapid increase until 9 Mm where it becomes shallower thereafter. We associate this radial gradient with the expansion of the magnetic field in the transition region between the chromosphere and the corona.

Keywords: Space plasmas, Interplanetary shocks, Solar eclipses, Solar wind, Solar corona, Solar transition region, Solar chromosphere
Investigating the CREDIT History of Supernova Remnants as Cosmic-Ray Sources. Supernova remnants (SNRs) have long been suspected to be the primary sources of Galactic cosmic rays. Over the past decades, great strides have been made in the modeling of particle acceleration, magnetic field amplification, and escape from SNRs. Yet while many SNRs have been observed in nonthermal emission in radio, X-rays, and gamma rays, there is no evidence for any individual object contributing to the locally observed flux. Here, we propose a particular spectral signature from individual remnants that is due to the energy-dependent escape from SNRs. For young and nearby sources, we predict fluxes enhanced by tens of percent in narrow rigidity intervals; given the percent-level flux uncertainties of contemporary cosmic-ray data, such features should be readily detectable. We model the spatial and temporal distribution of sources and the resulting distribution of fluxes with a Monte Carlo approach. The decision tree that we have trained on simulated data is able to discriminate with very high significance between the null hypothesis of a smooth distribution of sources and the scenario with a stochastic distribution of individual sources. We suggest that this cosmic-ray energy-dependent injection time (CREDIT) scenario be considered in experimental searches to identify individual SNRs as cosmic-ray sources.

Keywords: Cosmic ray detectors, Cosmic ray astronomy, Galactic cosmic rays, Supernova remnants, Cosmic ray sources, Milky Way Galaxy, Cosmic rays
Rates of Stellar Tidal Disruption Events around Intermediate-mass Black Holes. Rates of stellar tidal disruption events (TDEs) around supermassive black holes (SMBHs) have been extensively calculated using the loss cone theory, while theoretical work on TDE rates around intermediate-mass black holes (IMBHs) has been lacking. In this work, we aim to accurately calculate the IMBH TDE rates based on their black hole (BH) masses and the stellar profiles of their host galaxies obtained from the latest observations. We find that the TDE rate per galaxy for IMBHs in the center of small galaxies is similar to that of SMBH TDEs, while the TDE rate per cluster from IMBHs in globular clusters is much lower. Very interestingly, we show that the rate of IMBH TDEs generally increases with the BH mass, which is opposite to the trend seen in SMBH TDEs. As a result, the volumetric TDE rate peaks around a BH mass of 106 M⊙. The IMBH TDEs from galactic nuclei have an overall volumetric rate comparable to SMBH TDEs at ∼10‑7 Mpc‑3 yr‑1, and off-center IMBH TDEs from globular clusters have a volumetric rate that is one or two orders of magnitude lower, assuming that their occupation fraction varies within 10%–100%. Furthermore, we report that IMBH TDEs typically occur in the pinhole regime, which means that deeply plunging events are more likely for IMBH TDEs compared to SMBH TDEs.

Keywords: Globular star clusters, Intermediate-mass black holes, Galactic center, Tidal disruption, Stellar dynamics
MMS Observations of the Velocity-space Signature of Shock-drift Acceleration. Collisionless shocks play a key role in the heliosphere at planetary bow shocks by governing the conversion of the upstream bulk kinetic energy of the solar wind flow to other forms of energy in the downstream, including heating of the plasma species, acceleration of particles, and increase of magnetic energy. For a perpendicular collisionless shock with Alfvén Mach number MA = 5.5, we present here the first observational identification of the velocity-space signature of shock-drift acceleration of ions, previously predicted using kinetic numerical simulations, using a field–particle correlation analysis of Magnetospheric Multiscale observations of Earth's bow shock. Furthermore, by resolving the ion energization rates as a function of particle velocity, the field–particle correlation technique facilitates a clean quantitative separation of the energization rate of the reflected ions from that of the incoming ion beam, enabling a more complete characterization of the energy conversion at the shock.

Keywords: Space plasmas, Shocks, Planetary bow shocks, Plasma astrophysics
The Host Galaxy of the Hyperactive Repeating FRB 20240114A: Behind a Galaxy Cluster. We report on the optical spectroscopic observations of the host galaxy of the hyperactive repeating fast radio burst (FRB) FRB 20240114A. The host galaxy is a dwarf galaxy at a redshift of z = 0.1306 ± 0.0002. With a rest-frame coverage of 4300─7900 Å, we have detected Hα, Hβ, [O III] λλ4959,5007, [N II]λλ6548,6583, and [S II] λ6716 emission lines. The emission line ratios suggest that the ionization in the host galaxy is dominated by star formation. The star formation rate (SFR) derived from the Hα emission line is (0.06 ± 0.01) M⊙ yr−1, and the spectral energy distribution fitting suggests the lower limit of the SFR(UV) is 0.09 M⊙ yr−1. The stellar mass is (4.0 ± 1.8) × 108 M⊙, making the specific SFR  . The line ratios indicate an upper limit of a metallicity of 12 + log10([O/H]) ∼ 8.5. As the nearest dwarf host galaxy with a repeating FRB, the activity of FRB 20240114A and the properties of this host galaxy closely resemble those of FRB 20121102A and FRB 20190520B. The Hα-traced dispersion measure provided by the ionized gas of the host galaxy has a moderate contribution of ∼200 pc cm−3, assuming a warm ionized gas. We found that the distributions of the stellar mass versus SFR are significantly different between repeating and one-off FRBs, as determined by the MANOVA test with p = 0.0116.

Keywords: Starburst galaxies, Dwarf galaxies, Radio transient sources
SIRIUS: Identifying Metal-poor Stars Enriched by a Single Supernova in a Dwarf Galaxy Cosmological Zoom-in Simulation Resolving Individual Massive Stars. Metal-poor stars enriched by a single supernova (mono-enriched stars) are direct proof (and provide valuable probes) of supernova nucleosynthesis. Photometric and spectroscopic observations have shown that metal-poor stars have a wide variety of chemical compositions; the star's chemical composition reflects the nucleosynthesis process(es) that occurred before the star's formation. While the identification of mono-enriched stars enables us to study the ejecta properties of a single supernova, the fraction of mono-enriched stars among metal-poor stars remains unknown. Here we identify mono-enriched stars in a dwarf galaxy cosmological zoom-in simulation resolving individual massive stars. We find that the fraction of mono-enriched stars is higher for lower metallicity in stars with [Fe/H] &lt; ‑2.5. The percentages of mono-enriched stars are 11% at [Fe/H] = ‑5.0 and 1% at [Fe/H] = ‑2.5, suggesting that most metal-poor stars are affected by multiple supernovae. We also find that mono-enriched stars tend to be located near the center of the simulated dwarf. Such regions will be explored in detail in upcoming surveys such as the Prime Focus Spectrograph on the Subaru telescope.

Keywords: Galaxy formation, Population III stars, Nucleosynthesis, Dwarf galaxies, Population II stars
Evidence for a Volcanic Atmosphere on the Sub-Earth L 98-59 b. Assessing the prevalence of atmospheres on rocky planets around M-dwarf stars is a top priority of exoplanet science. High-energy activity from M dwarfs can destroy the atmospheres of these planets, which could explain the lack of atmosphere detections to date. Volcanic outgassing has been proposed as a mechanism to replenish the atmospheres of tidally heated rocky planets. L 98-59 b, a sub-Earth transiting a nearby M dwarf, was recently identified as the most promising exoplanet to detect a volcanic atmosphere. We present the transmission spectrum of L 98-59 b from four transits observed with JWST NIRSpec G395H. Although the airless model provides an adequate fit to the data based on its χ2, an SO2 atmosphere is preferred by 3.6σ over a flat line in terms of the Bayesian evidence. Such an atmosphere would likely be in a steady state where volcanism balances escape. If so, L 98-59 b must experience at least eight times as much volcanism and tidal heating per unit mass as Io. If volcanism is driven by runaway melting of the mantle, we predict the existence of a subsurface magma ocean in L 98-59 b extending up to Rp ∼ 60%–90%. An SO2-rich volcanic atmosphere on L 98-59 b would be indicative of an oxidized mantle with an oxygen fugacity of fO2 &gt; IW + 2.7, and it would imply that L 98-59 b must have retained some of its volatile endowment despite its proximity to its star. Our findings suggest that volcanism may revive secondary atmospheres on tidally heated rocky planets around M dwarfs.

Keywords: Extrasolar rocky planets, Exoplanet atmospheric composition , Transmission spectroscopy, James Webb Space Telescope, Volcanism
Extremely Dense Gas around Little Red Dots and High-redshift Active Galactic Nuclei: A Nonstellar Origin of the Balmer Break and Absorption Features. The James Webb Space Telescope (JWST) has uncovered low-luminosity active galactic nuclei (AGNs) at high redshifts of z ≳ 4–7, powered by accreting black holes with masses of ∼106‑8 M⊙. One remarkable distinction of these JWST-identified AGNs, compared to their low-redshift counterparts, is that at least ∼20% of them present Hα and/or Hβ absorption, which must be associated with extremely dense (≳109 cm‑3) gas in the broad-line region or its immediate surroundings. These Balmer absorption features unavoidably imply the presence of a Balmer break caused by the same dense gas. In this Letter, we quantitatively demonstrate that a Balmer break can form in AGN spectra without stellar components, when the accretion disk is heavily embedded in dense neutral gas clumps with densities of ∼109‑11 cm‑3, where hydrogen atoms are collisionally excited to the n = 2 states and effectively absorb the AGN continuum at the bluer side of the Balmer limit. The nonstellar origin of a Balmer break offers a potential solution to the large stellar masses and densities inferred for little red dots (LRDs) when assuming that their continuum is primarily due to stellar light. Our calculations indicate that the observed Balmer absorption blueshifted by a few hundred km s‑1, which suggests the presence of dense outflows in the nucleus at rates exceeding the Eddington value. Other spectral features such as higher equivalent widths of broad Hα emission and presence of O I lines observed in high-redshift AGNs including LRDs align with the predicted signatures of a dense super-Eddington accretion disk.

Keywords: Supermassive black holes, Galaxy formation, High-redshift galaxies, Quasars
Maximal Jet Energy of Gamma-Ray Bursts through the Blandford–Znajek Mechanism. Gamma-ray bursts (GRBs) are among the most energetic events in the Universe, driven by relativistic jets launched from black holes (BHs) formed during the collapse of massive stars or after the merger of two neutron stars. The jet power depends on the BH spin and the magnetic flux accreted onto it. In the standard thin disk model, jet power is limited by insufficient magnetic flux, even when the spin approaches maximum possible value. In contrast, the magnetically arrested disk (MAD) state limits jet energy by extracting significant angular momentum, braking BH rotation. We propose a unified model incorporating both standard thin disk and MAD states, identifying a universal curve for jet power per accretion rate as a function of the magnetic flux ratio,  , at spin equilibrium. For long GRBs (lGRBs), the model predicts a maximum jet energy of ∼1.5% of the accretion energy, occurring at Δeq ∼ 0.4, where the BH equilibrium spin is a ∼ 0.5. Both long and short GRBs are unlikely to be produced by a MAD: for short GRBs, this requires an accreted mass orders of magnitude smaller than that available, while for lGRBs, the narrow progenitor mass distribution challenges the ability to produce the observed broad distribution of jet energies. This framework provides a consistent explanation for both standard and luminous GRBs, emphasizing the critical role of magnetic flux. Both long and short GRBs require magnetic flux distributions that peak around 1027 G cm2.

Keywords: Accretion, Gamma-ray bursts, Relativistic jets, Astrophysical black holes
Strong Rest-UV Emission Lines in a "Little Red Dot" Active Galactic Nucleus at z = 7: Early Supermassive Black Hole Growth alongside Compact Massive Star Formation?. JWST has now revealed a population of broad-line active galactic nuclei (AGN) at z ≳ 4 characterized by a distinctive spectral energy distribution shape, with a very red rest-frame optical and very blue rest-frame UV continuum. While the optical continuum is thought to originate from the accretion disk, the origin of the UV continuum has been largely unclear. We report the detection of the strong rest-frame UV emission lines of C III] λλ1907, 1909 and C IV λλ1549, 1551 in a "little red dot" AGN, COS-66964. Spectroscopically confirmed at z = 7.0371, COS-66964 exhibits broad Hα emission (FWHM ∼ 2000 km s‑1) and weak broad Hβ, implying significant dust attenuation to the broad-line region ( ). The Hα line width implies a central supermassive black hole (SMBH) mass of   M⊙ and an Eddington ratio λ ∼ 0.3–0.5. While marginal He II λ4687 and [Fe X] λ6376 detections further indicate that the AGN dominates in the rest-frame optical, the nondetection of He II λ1640 in the UV despite high EW C III] and C IV (∼35 Å) is more consistent with photoionization by massive stars. The nondetection of Mg II λλ2800 is similarly inconsistent with an AGN scattered light interpretation. Assuming the rest-frame UV is dominated by stellar light, we derive a stellar mass of  , implying an elevated MBH/M⋆ ratio ∼2 orders of magnitude above the local relation, but consistent with other high-z AGN discovered by JWST. The source is unresolved in all bands, implying a very compact size ≲200 pc in the UV. This suggests that the simultaneous buildup of compact stellar populations (i.e., galaxy bulges) and the central SMBH is ongoing even at z ≳ 7.

Keywords: AGN host galaxies, Active galactic nuclei, Galaxy evolution, Reionization, High-redshift galaxies, Galaxies
Signatures of Rapidly Rotating Stars with Chemically Homogeneous Evolution in the First Galaxies. The James Webb Space Telescope (JWST) has revealed an unexpectedly high abundance of UV luminous galaxies at redshifts z ≳ 10, challenging "standard" galaxy formation models. This study investigates the role of rapidly rotating (massive) stars undergoing chemically homogeneous evolution (CHE) in reconciling this potential tension. These stars are more compact, hotter, and exhibit enhanced UV emission. We find that the rest-frame UV luminosity of star-forming galaxies can be significantly enhanced by a factor of ∼3‑6 when CHE stars above a minimum initial mass of   account for more than half of the total stellar mass following a Salpeter initial mass function. As a result, the UV luminosity functions observed at z ∼ 12‑16 can be reproduced with less extreme values of star formation efficiency and UV luminosity stochastic variability. Our results highlight the potential of CHE in explaining the UV-bright galaxy populations detected by JWST and call for future work to explore the broader astrophysical implications of CHE and its associated phenomena in the early universe, such as gamma-ray bursts, compact object binaries, and metal enrichment.

Keywords: Early universe, Population III stars, James Webb Space Telescope, Population II stars, High-redshift galaxies, Stellar evolution
The Cold Jupiter Eccentricity Distribution is Consistent with EKL Driven by Stellar Companions. The large eccentricities of cold Jupiters and the existence of hot Jupiters have long challenged theories of planet formation. A proposed solution to both of these puzzles is high-eccentricity migration, in which an initially cold Jupiter is excited to high eccentricities before being tidally circularized. Secular perturbations from an inclined stellar companion are a potential source of eccentricity oscillations, a phenomenon known as the Eccentric Kozai–Lidov (EKL) mechanism. Previous studies have found that the cold Jupiter eccentricity distribution produced by EKL is inconsistent with observations. However, these studies assumed all planets start on circular orbits. Here, we revisit this question, considering that an initial period of planet–planet scattering on ∼Myr timescales likely places planets on slightly eccentric orbits before being modulated by EKL on ∼Myr–Gyr timescales. Small initial eccentricities can have a dramatic effect by enabling EKL to act at lower inclinations. We numerically integrate the secular hierarchical three-body equations of motion, including general relativity and tides, for populations of cold giant planets in stellar binaries with varied initial eccentricity distributions. For populations with modest initial mean eccentricities, the simulated eccentricity distribution produced by EKL is statistically consistent with the observed eccentricities of cold single-planet systems. The lower eccentricities in a multiplanet control sample suggest planetary companions quench stellar EKL. We show that scattering alone is unlikely to reproduce the present-day eccentricity distribution. We also calculate predictions for the inclinations and stellar obliquities in binary systems with cold Jupiters.

Keywords: Exoplanet dynamics, Planetary system evolution, Exoplanet migration, Exoplanets, Planetary system formation, Extrasolar gaseous planets