Sazuna/UAT_keywords huggingface dataset:
Pressure-anisotropy-mediated Helical Dynamo in Turbulent Collisionless Plasmas. The origin of coherent, near-equipartitioned magnetic fields in the universe remains poorly understood, especially in collisionless scenarios. By means of theoretical modeling that includes indispensable kinetic effects and fully kinetic particle-in-cell simulation that contains sufficient scale separation, we self-consistently show that the collisionless large-scale dynamo is quite efficient and the system-scale coherent fields can be generated from kinetic-scale seeds under a turbulent helical drive. We find that, by triggering kinetic mirror and firehose instabilities, the pressure anisotropy—a kinetic effect that is unresolved in conventional magnetohydrodynamics—is the key physics that produces net magnetic helicity that can be inversely transferred to large scales. The magnetic helicity generation rate can be formulated as  , where urms is the turbulent velocity and Lin is the driving scale. Our results profoundly refine the picture of cosmic dynamos and potentially resolve the critical issue of dynamo quench.

Keywords: Cosmic magnetic fields theory, Plasma astrophysics, Magnetic fields, Plasma physics
Propagating Bright Knots in the Chromospheric Fibrils. The solar chromosphere is a crucial layer for resolving the problem of atmospheric heating. There are many bright features, which are considered as the thermal signals for heating the atmosphere, and these features are suggested to have resulted from either magnetic reconnection or wave dissipation. It has been reported that a large number of propagating bright knots are detected in the chromosphere and corona. In this paper, we employ the high-resolution chromospheric Hα data from the New Vacuum Solar Telescope to study the propagating bright knots. As the propagating bright knots move along the chromospheric fibrils, we select isolated and clear fibrils and track the knots along these fibrils. While the number of knots in a fibril region is equal to or greater than 5, the fibril and the knots are recorded. Based on the data on 2019 September 4, we detected 98 knots, and these knots move along 13 fibrils. On 2019 November 2, 87 knots, which move along 12 fibrils, were recorded. These propagating bright knots have an average area of around 0.8 Mm2, with propagating distances from 190 to 2450 km, propagating velocities from 5 to 51 km s‑1, and an average lifetime of 71 s. To examine the relationship between the knots and the photospheric magnetic fields, we measure the field underneath these knots. The average magnetic flux densities are less than 10 Gauss, comparable with the noise level. We suggest that these knots are not produced by magnetic reconnection, but rather by wave dissipation.

Keywords: Magnetohydrodynamics, Solar chromosphere, Solar fibrils
Resonant Damping and Instability of Propagating Magnetohydrodynamic Body Modes in a Flux Tube with Shear Flow under Photospheric Conditions. The influence of shear flow on resonant absorption is theoretically investigated for propagating magnetohydrodynamic body modes in cusp (slow) and Alfvén continua in a cylindrical flux tube under photospheric conditions. An analytical dispersion relation for resonant absorption in the presence of flow shear is developed by assuming a thin boundary layer. The numerical solutions reveal that the presence of flow shear has a rather negative impact on the resonant absorption of the body mode compared to the surface modes. As the flow shear increases, it first slightly increases the strength of resonant absorption for the forward body modes and then decreases it below the strength of no flow shear case for both resonances. It is also found that as the flow shear increases, the range of the axial wavenumber and wave frequency for the cusp resonance decreases when the wave frequency is close to the upper boundary of the cusp continuum. For the backward body modes, the strength of the resonance absorption decreases with the increment of the flow shear. When the flow shear is sufficiently large, the waves propagate in the forward direction, and their amplitude grows with a small increment.

Keywords: Solar active region magnetic fields, Magnetohydrodynamics, Solar photosphere, Solar physics, Alfven waves, Solar oscillations
Rotating Neutron Stars with Relativistic Ab Initio Calculations. The equation of state (EOS) of extremely dense matter is crucial for understanding the properties of rotating neutron stars. Starting from the widely used realistic Bonn potentials rooted in a relativistic framework, we derive EOSs by performing state-of-the-art relativistic Brueckner–Hartree–Fock calculations in the full Dirac space. The self-consistent and simultaneous consideration of both positive- and negative-energy states (NESs) of the Dirac equation allows us to avoid the uncertainties present in calculations where NESs are treated using approximations. To manifest the impact of rotational dynamics, several structural properties of neutron stars across a wide range of rotation frequencies and up to the Keplerian limit are obtained, including the gravitational and baryonic masses, the polar and equatorial radii, and the moments of inertia. Our theoretical predictions align well with the latest astrophysical constraints from observations of massive neutron stars and joint mass–radius measurements. The maximum mass for rotating configurations can reach up to 2.93 M⊙ for Bonn A potential, while the radius of a 1.4 M⊙ neutron star in the nonrotating case can be extended to around 17 km through constant baryonic mass sequences. Relations with good universalities between the Keplerian frequency and static mass as well as radius are obtained, from which the radius of the black widow PSR J0952-0607 is predicted to be less than 19.58 km. Furthermore, to understand how rotation deforms the equilibrium shape of a neutron star, the eccentricity is also calculated. The approximate universality between the eccentricity at the Keplerian frequency and the gravitational mass is found.

Keywords: Neutron stars, Nuclear astrophysics
A 22 yr Cycle of the Network Topology of Solar Active Regions. In this paper, solar cycles 21–24 were compared using complex network analysis. A network was constructed for these four solar cycles to facilitate the comparison. In these networks, the nodes represent the active regions of the Sun that emit flares, and the connections correspond to the sequence of solar flares over time. This resulted in a directed network with self-connections allowed. The model proposed by Abe and Suzuki for earthquake networks was followed. The incoming degree for each node was calculated, and the degree distribution was analyzed. It was found that for each solar cycle, the degree distribution follows a power law, indicating that solar flares tend to appear in correlated active zones rather than being evenly distributed. Additionally, a variation in the characteristic exponent γ for each cycle was observed, with higher values in even cycles compared to odd cycles. A more detailed analysis was performed by constructing 11 yr networks and shifting them in 1 yr intervals. This revealed that the characteristic exponent shows a period of approximately 22 yr coincident with the Hale cycle, suggesting that the complex networks provide information about the solar magnetic activity.

Keywords: Solar cycle, Solar flares, Solar dynamo, Solar active regions, Solar physics, Solar magnetic fields, Solar activity
Observations of the Ultraviolet-bright Star III-60 in the Globular Cluster NGC 6723. We have analyzed archival far-ultraviolet spectra of the UV-bright star III-60 in the globular cluster NGC 6723 obtained with the Far Ultraviolet Spectroscopic Explorer and the Cosmic Origins Spectrograph. We find that the star's photospheric parameters (effective temperature Teff = 44,800 ± 1200 K, surface gravity  , and helium abundance  ) are consistent with the values derived from its optical spectrum, suggesting that optically derived values are generally accurate for evolved stars with Teff ≲ 50,000 K. Relative to the cluster's red giant branch stars, III-60 is enhanced in nitrogen and depleted in carbon and oxygen. The star exhibits strong P Cygni profiles in both components of the N V λ1240 doublet, but the resonance lines of other species show no evidence of a stellar wind. The star's effective temperature and luminosity place it on the evolutionary tracks of stars evolving from the blue horizontal branch, but its high mass (∼1.2 M⊙) indicates that it is the product of a stellar merger. Its helium, carbon, and nitrogen abundances suggest that it is following an evolutionary path similar to that of the low-carbon, intermediate helium-rich hot subdwarfs.

Keywords: Stellar abundances, Ultraviolet spectroscopy, Stellar atmospheres, Stellar evolution
The Influence of General Relativity on the Spins of Celestial Bodies in Inclined Orbits. Through the Rossiter–McLaughlin effect, several hot Jupiters have been found to exhibit spin–orbit misalignment and even retrograde orbits. The high obliquity observed in these planets can be attributed to two primary formation mechanisms, as summarized in the existing literature. First, the host star's spin becomes misaligned with the planetary disk during the late stages of star formation, primarily due to chaotic accretion and magnetic interactions between the star and the planetary disk. Second, the orbital inclination of an individual planet can be excited by dynamical processes such as planet–planet scattering, the Lidov–Kozai cycle, and secular chaos within the framework of Newtonian mechanics. This study introduces a third mechanism, where, within the framework of general relativity, the post-Newtonian spin–orbit coupling term induces precession of the host star's spin around the orbital angular momentum. The orbital inclination, relative to a reference plane, can expand the range of deviation in the spatial orientation of the bodies' spins from the plane's normal. The varying amplitude and period of spin precession for both the star and the planet are derived theoretically, and the results, which can be applied without restriction, agree well with numerical simulations.

Keywords: Exoplanet evolution, Solar-planetary interactions, Hot Jupiters
Mach Number Scaling of Foreshock Magnetic Fluctuations at Quasi-parallel Bow Shocks and Their Role in Magnetospheric Driving Throughout the Solar System. Upstream of quasi-parallel bow shocks, reflected ions generate ion–ion instabilities. The resulting magnetic fluctuations can advect through the shock and interact with planetary magnetospheres. The amplitude of magnetic fluctuations depends on the strength of the shock, quantified by the Alfvén Mach number (MA), which is the ratio of solar wind velocity to the local Alfvén velocity. With increasing heliocentric distance, the solar wind MA generally increases, such that Mercury typically experiences a lower MA ∼ 5 compared to Earth (MA ∼ 8), and Mars a slightly higher MA ∼ 9. Farther out in the solar system, Saturn has even higher MA (∼10). However, the solar wind flow is highly irregular, and on top of solar cycle variations these values for average MA at each planet do not capture extreme events. Statistical analysis of OMNIWeb observations from 2015 to 2023 shows that sustained (30 minutes or more) high MA (30–100) occurs at Earth about once a month. Using a selection of events in the ion foreshock regions of Mercury, Earth, Mars, and Saturn, a linear scaling is calculated for the maximum magnetic fluctuation amplitude as a function of MA. The resulting slope is ∼0.2. Based on the dominant fluctuation frequency for the largest-amplitude events at each planet, it is found that Mars exists in a special regime where the wave period of the magnetic fluctuations can be similar to or longer than the magnetospheric convection timescale, making Mars more susceptible to space weather effects associated with foreshock fluctuations.

Keywords: Planetary magnetospheres, Planetary bow shocks
Characteristics of the IBEX Ribbon and Their Implications for a Source Region Outside the Heliopause. This paper presents a comprehensive exploration of the Interstellar Boundary Explorer energetic neutral atom (ENA) ribbon, focusing on its spatial and temporal variations over 14 yr. Methodological advancements, including a refined map modeling procedure and a new ribbon separation technique with appropriate error propagation, enable a detailed investigation of the ribbon's features. Utilizing statistically robust metrics, this study reveals details of the ribbon across energy and time. Key findings include energy- and time-dependent variations in flux, angular radius, ribbon profile width, and higher moments. By applying these metrics, we reveal new complexity to the evolution of the ribbon over time, highlighting the nuanced relationship between it and the solar wind. Furthermore, the study examines for the first time the ribbon as it passes through the starboard/heliotail region (LonEC 120°─180°), revealing properties distinct from other portions of the ribbon. The analysis uncovers an anticorrelation between ribbon width and flux, which provides quantitative support for a multisource ribbon created by a combination of solar wind neutrals that generate a spatiall narrow ribbon component and heliosheath neutrals giving rise to a broad component. Finally, differences in the temporal evolution of the ENA flux at different energies provide additional support that the location of the ribbon source region is beyond the heliopause.

Keywords: Interstellar magnetic fields, Solar wind, Heliosphere
Similarities and Differences between ICME-driven Shocks Observed by VEX (∼0.72 au) and WIND (∼1.0 au). The features of interplanetary shocks driven by interplanetary coronal mass ejections (ICMEs) observed by WIND (∼1.0 au) and Venus Express (VEX; ∼0.72 au) during the same period are statistically analyzed by comparing their similarities and differences. It is found that the proportion of ICME-driven shocks in all shocks decreases slightly from ∼0.72 to ∼1 au. The yearly occurrence of ICME-driven shocks at both ∼0.72 and ∼1 au roughly follows the sunspot cycle, while the magnetic field ratio does not show such a correspondence. In each year, the annual medians of the shock angle for ICME-driven shocks at ∼1 au are consistently larger than those at ∼0.72 au, and the annual medians of the magnetic field ratio for events at ∼1 au are slightly smaller than those at ∼0.72 au. Planar magnetic structures (PMSs) downstream of ICME-driven shocks are also analyzed. Approximately 28.57% of the detected PMS events from VEX observations and 28.84% from WIND observations cover the entire 2 hr intervals downstream of the shocks, which are referred to as full PMS events. Through comparative analysis for VEX and WIND observations, it is found that strong and quasi-perpendicular ICME-driven shocks are the most preferable conditions for full PMS formation.

Keywords: Solar coronal mass ejections, Interplanetary shocks, Interplanetary magnetic fields, Astronomy data analysis
Simulating High-redshift Galaxies: Enhancing UV Luminosity with Star Formation Efficiency and a Top-heavy IMF. Recent findings from photometric and spectroscopic JWST surveys have identified examples of high-redshift galaxies at z ≳ 10. These high-z galaxies appear to form much earlier and exhibit greater UV luminosity than predicted by theoretical work. In this study, our goal is to reproduce the brightness of these sources by simulating high-redshift galaxies with virial masses Mvir = 109–1010 M⊙ at z &gt; 10. To achieve this, we conduct cosmological hydrodynamic zoom-in simulations, modifying baryonic subgrid physics, and post-process our simulation results to confirm the observability of our simulated galaxies. Specifically, we enhanced star formation activity in high-redshift galaxies by either increasing the star formation efficiency up to 100% or adopting a top-heavy initial mass function (IMF). Our simulation results indicate that both increasing star formation efficiency and adopting a top-heavy IMF play crucial roles in boosting the UV luminosity of high-redshift galaxies, potentially exceeding the limiting magnitude of JWST surveys in earlier epochs. In particular, the episodic starburst resulting from enhanced star formation efficiency may explain the high-redshift galaxies observed by JWST, as it evacuates dust from star-forming regions, making the galaxies more observable. We demonstrate this correlation between star formation activity and dust mass evolution within the simulated galaxies. Also, adopting a top-heavy IMF could enhance observability due to an overabundance of massive stars, although it may also facilitate rapid metal enrichment. Using our simulation results, we derive several observables such as effective radius, UV slope, and emission-line rates, which could serve as valuable theoretical estimates for comparison with existing spectroscopic results and forthcoming data from the JWST NIRSpec and MIRI instruments.

Keywords: James Webb Space Telescope
UNCOVER: The Rest-ultraviolet to Near-infrared Multiwavelength Structures and Dust Distributions of Submillimeter-detected Galaxies in A2744. With the wavelength coverage, sensitivity, and high spatial resolution of JWST, it is now possible to peer through the dust attenuation to probe the rest-frame near-infrared (NIR) and stellar structures of extremely dusty galaxies at cosmic noon (z ∼ 1‑3). In this paper we leverage the combined Atacama Large Millimeter/submillimeter Array (ALMA) and JWST/Hubble Space Telescope coverage in A2744 to study the multiwavelength (0.5‑4.4 μm) structures of 11 submillimeter detected galaxies at z ∼ 0.9‑3.5 that are fainter than bright "classical" submillimeter galaxies, seven of which are detected in deep X-ray data. While these objects reveal a diversity of structures and sizes, all are smaller and more concentrated toward longer wavelengths. Of the X-ray-detected objects, only two show evidence for appreciable active galactic nucleus (AGN) flux contributions (at ≳2 μm). Excluding the two AGN-dominated objects, the smaller long-wavelength sizes indicate that their rest-frame NIR light profiles, inferred to trace their stellar mass profiles, are more compact than their optical profiles. The submillimeter detections and visible dust lanes suggest that centrally concentrated dust is a key driver of the observed color gradients. Further, we find that more concentrated galaxies tend to have lower size ratios (rest-frame NIR to optical); this suggests that the galaxies with the most compact light distributions also have the most concentrated dust. The 1.2 mm flux densities and size ratios of these nine objects suggest that both total dust quantity and geometry impact these galaxies' multiwavelength structures. Upcoming higher-resolution 1.2 mm ALMA imaging will facilitate joint spatially resolved analysis and will directly test the dust distributions within this representative submillimeter population.

Keywords: Galaxy formation, Galaxy structure, Galaxy evolution, Galaxy radii
A SPectroscopic Survey of Biased Halos in the Reionization Era (ASPIRE): Spectroscopically Complete Census of Obscured Cosmic Star Formation Rate Density at z = 4–6. We present a stringent measurement of the dust-obscured star formation rate density (SFRD) at z = 4–6 from the ASPIRE JWST Cycle-1 medium and ALMA Cycle-9 large program. We obtained JWST/NIRCam grism spectroscopy and ALMA 1.2 mm continuum map along 25 independent quasar sightlines, covering a total survey area of ∼35 arcmin2 where we search for dusty star-forming galaxies (DSFGs) at z = 0–7. We identify eight DSFGs in seven fields at z = 4–6 through the detection of Hα or [O III] λ5008 lines, including fainter lines such as Hβ, [O III] λ4960, [N II] λ6585, and [S II] λλ6718,6733 for six sources. With this spectroscopically complete DSFG sample at z = 4–6 and negligible impact from cosmic variance (shot noise), we measure the infrared luminosity function (IRLF) down to LIR ∼ 2 × 1011 L⊙. We find flattening of IRLF at z = 4–6 towards the faint end (power-law slope  ). We determine the dust-obscured cosmic SFRD at this epoch to be  . This is significantly higher than previous determinations using ALMA data in the Hubble Ultra Deep Field, which is void of DSFGs at z = 4–6 because of strong cosmic variance (shot noise). We conclude that the majority (66% ± 7%) of cosmic star formation at z ∼ 5 is still obscured by dust. We also discuss the uncertainty of SFRD propagated from far-IR spectral energy distribution and IRLF at the bright end, which will need to be resolved with future ALMA and JWST observations.

Keywords: Starburst galaxies, James Webb Space Telescope, Galaxy evolution, High-redshift galaxies, Luminous infrared galaxies
Rare Occasions: Tidal Disruption Events Rarely Power the AGNs Observed in Dwarf Galaxies. Tidal disruption events (TDEs) could be an important growth channel for massive black holes in dwarf galaxies. Theoretical work suggests that the observed active galactic nuclei (AGNs) in dwarf galaxies are predominantly TDE-powered. To assess this claim, we perform variability analyses on the dwarf-hosted AGNs detected in the 7 Ms Chandra Deep Field-South survey, with observations spanning ≈16 yr. Based on the spectral energy distribution modeling with X-CIGALE, we select AGNs hosted by dwarf galaxies (stellar mass below 1010 M ⊙). We focus on X-ray sources with full-band detections, leading to a sample of 78 AGNs (0.122 ≤ z ≤ 3.515). We fit the X-ray light curves with a canonical TDE model of t ‑5/3 and a constant model. If the former outperforms the latter in fitting quality for a source, we consider the source as a potential TDE. We identify five potential TDEs, constituting a small fraction of our sample. Using true- and false-positive rates obtained from fitting models to simulated light curves, we perform Bayesian analysis to obtain the posterior of the TDE fraction for our sample. The posterior peaks close to zero (2.56%), and we obtain a 2σ upper limit of 9.80%. Therefore, our result indicates that the observed AGNs in dwarf galaxies are not predominantly powered by TDEs.

Keywords: AGN host galaxies, Tidal disruption, Dwarf galaxies, X-ray active galactic nuclei
Vertical Shear Instability in Thermally Stratified Protoplanetary Disks. I. A Linear Stability Analysis. Vertical shear instability (VSI), driven by a vertical gradient of rotational angular velocity, is a promising source of turbulence in protoplanetary disks. We examine the semiglobal stability of thermally stratified disks and find that the VSI consists of surface and body modes: surface modes are confined to regions of strong shear, while body modes extend perturbations across the disk, consistent with the previous findings. In thermally stratified disks, surface modes bifurcate into two branches. The branch associated with the strongest shear at mid-height exhibits a higher growth rate compared to the branch near the surfaces. Surface modes generally grow rapidly and require a high radial wavenumber kR, whereas body mode growth rates increase as kR decreases. Thermal stratification enhances the growth rates of both surface and body modes and boosts VSI-driven radial kinetic energy relative to vertical energy. Our results suggest that simulations will initially favor surface modes with large kR, followed by an increase in body modes with smaller kR, with faster progression in more thermal stratified disks.

Keywords: Accretion, Internal waves, Hydrodynamics, Analytical mathematics, Protoplanetary disks