Sazuna/UAT_keywords huggingface dataset:
Understanding Stellar Mass–Metallicity and Size Relations in Simulated Ultrafaint Dwarf Galaxies. Reproducing the physical characteristics of ultrafaint dwarf galaxies (UFDs) in cosmological simulations is challenging, particularly with respect to stellar metallicity and galaxy size. To investigate these difficulties in detail, we conduct high-resolution simulations (Mgas ∼ 60 M⊙, MDM ∼ 300 M⊙) on six UFD analogs (Mvir ∼ 108–109 M⊙, M⋆ ∼ 103–2.1 × 104 M⊙ at z = 0). Our findings reveal that the stellar properties of the UFD analogs are shaped by diverse star-forming environments from multiple progenitor halos in the early Universe. Notably, our UFD analogs exhibit a better match to the observed mass–metallicity relation, showing higher average metallicity compared to other theoretical models, though our results remain 0.5–1 dex lower than for observed UFDs. The metallicity distribution functions (MDFs) of our simulated UFDs lack high-metallicity stars ([Fe/H]≥ ‑2.0) while containing low-metallicity stars ([Fe/H] &lt; ‑4.0). Excluding these low-metallicity stars, our results align well with the MDFs of observed UFDs. However, forming stars with higher metallicity (‑2.0 ≤ [Fe/H]max ≤ ‑1.5) remains a challenge, due to the difficulty of sustaining metal enrichment during the brief star formation period before cosmic reionization. Additionally, our simulations show extended outer structures in UFDs, similar to recent Milky Way UFD observations, resulting from dry mergers between progenitor halos. To ensure consistency, we adopt the same fitting method commonly used in observations to derive the half-light radius. We find that this method tends to produce lower values compared to direct calculations and struggles to accurately describe the extended outer structures.

Keywords: Dwarf galaxies
Shadow-based Framework for Estimating Transition Disk Geometries. Some transition disks host misaligned inner disks with radii of several astronomical units. Understanding the geometric and physical properties of these misaligned disks is essential for advancing terrestrial planet formation models. This study introduces a novel method to infer the three-dimensional structures of both inner and outer disks by analyzing nonaxisymmetric shadows and the horizon in optical and infrared scattered light images of the outer disk. This method was applied to the HD 100453 system, in which infrared scattered light images from the Very Large Telescope revealed disk shadows. These results indicate that the inner disk is misaligned by ∼70° relative to the outer disk, which is consistent with the results of previous studies. The aspect ratio of the inner disk surface was estimated to be 0.17, which may reflect the surface height of the optically thick dusty component due to vertical lofting by MHD winds or turbulence. In addition, the surface height distribution of the outer disk was characterized, providing novel insights into its vertical structure.

Keywords: Infrared astronomy, Protoplanetary disks, Optical astronomy
Estimating Global Ejecta Mass Ratios in Tycho's Supernova Remnant. In this work, as a follow-up to our similar analysis of Kepler's supernova remnant (SNR), we estimate total mass ratios of various ejecta elements in Tycho's SNR using Suzaku X-ray data. In our spectral analysis, we account for uncertainties arising from Suzaku's effective area calibration (5%─15%) and from the unknown filling factors of the various plasma components in our spectral model (1%─10%). We compare our calculated ejecta mass ratios to results from previous X-ray analyses of Tycho's SNR and to the nucleosynthesis results from Type Ia supernova simulations. Our estimated ejecta mass ratios for Tycho's SNR are only consistent with simulations that use a ∼90% attenuated 12C+16O reaction rate (as for Kepler's SNR), are inconsistent with simulations involving a double detonation of a thick helium layer, and support a Type Ia explosion of normal luminosity where ∼85% of the ejecta has been heated by the reverse shock.

Keywords: X-ray astronomy, Ejecta, High energy astrophysics, X-ray telescopes, Supernova remnants, Calibration, Spectroscopy, Markov chain Monte Carlo
Improving Porosity Calculation Methods and Proposing a New Model Universally Applicable to Large- and Medium-sized Planetary Objects. Our work was aimed at the improvement of two main already existing methods of porosity calculation on a planetary scale in order to expand these methods to be applicable to exoplanetary interiors. In addition to implementing some improvements in the used approach, we also wanted to provide a new, more sophisticated model with the combination of the two base models. Utilizing our combined model we aimed to provide results regarding the porosity structure of the interior of four planetary bodies of the solar system (Enceladus, Earth, Mars, and the Moon), chosen as case studies. Taking a method that is based on fitted functions to experimental data from geological environments, and a separate method based on the temporal evolution of planetary interiors governed by thermodynamic processes, we developed a combined model, which incorporates the advantages of both base models. The proposed new model produced a pore compaction depth of 62.52 km for the core of Enceladus, 4.5 km for Earth, 19.96 km for Mars, and 32.51 km for the Moon. Moreover, we have discovered differing trends between the effect of changes in geothermal gradient and surface temperatures across planetary objects of different sizes.

Keywords: Exoplanet structure, Astrobiology, Planetary interior, Planetary science
Luminosity and Stellar Mass Functions of Faint Photometric Satellites around Spectroscopic Central Galaxies from DESI Year-1 Bright Galaxy Survey. We measure the luminosity functions (LFs) and stellar mass functions (SMFs) of photometric satellite galaxies around spectroscopically identified isolated central galaxies (ICGs). The photometric satellites are from the DESI Legacy Imaging Surveys (DR9), while the spectroscopic ICGs are selected from the DESI Year-1 BGS sample. We can measure satellite LFs down to r-band absolute magnitudes of Mr,sat ∼ ‑7, around ICGs as small as  7.1&lt;log10M∗,ICG/M⊙&lt;7.8 , with the stellar mass of ICGs measured by the DESI FASTSPECFIT pipeline. The satellite SMF can be measured down to  log10M∗,sat/M⊙∼5.5 . Interestingly, we discover that the faint/low-mass end slopes of satellite LFs/SMFs become steeper with the decrease in the stellar masses of host ICGs, with smaller and nearby host ICGs capable of being used to probe their fainter satellites. The steepest slopes can be ‑2.298 ± 0.656 and ‑2.888 ± 0.916 for satellite LF and SMF, respectively. Detailed comparisons are performed between the satellite LFs around ICGs selected from DESI BGS or from the SDSS NYU-VAGC spectroscopic Main galaxies over  7.1&lt;log10M∗,ICG/M⊙&lt;11.7 , showing reasonable agreement, but we show that differences between DESI and SDSS stellar masses for ICGs play a role to affect the results. We also compare measurements based on DESI FASTSPECFIT and CIGALE stellar masses used to bin ICGs, with the latter including the modeling of active galactic nuclei based on Wide-field Infrared Survey Explorer photometry, and we find good agreements in the measured satellite LFs by using either of the DESI stellar mass catalogs.

Keywords: Galaxy evolution, Galaxy luminosities, Galaxy groups, Galaxy counts
Formation of a Possible Black-hole Ultracompact X-Ray Binary with the Shortest Orbital Period. In the bulge of M31, the Chandra observations discovered a possible black hole (BH) ultracompact X-ray binary (UCXB) Seq.1 with an orbital period of 7.7 minutes and a maximum X-ray luminosity  LX=1.09‑0.01+0.02×1038ergs‑1  in the 0.5–8 keV band. The minimum orbital period of the BH UCXBs predicted by the standard magnetic braking (MB) model is longer than 8.3 minutes. In this work, we investigate whether the convection- and rotation-boosted (CARB) MB prescription can account for the formation of a BH UCXB such as Seq.1. Our detailed stellar evolution models indicate that the CARB MB law can drive isolated BH–main-sequence (MS) binaries to evolve toward BH UCXBs with an orbital period of 7.7 minutes, in which a low-mass white dwarf transfers the material onto a BH in a short-term mass-transfer episode, producing an X-ray luminosity of ∼1038 erg s‑1. We also obtain an initial parameter space of BH–MS binaries as the progenitors of Seq.1 in the donor-star masses and orbital periods plane, which can be applied to future population synthesis simulations. If Seq.1 is indeed a BH UCXB, future spaceborne gravitational wave (GW) detectors can detect the low-frequency GW signals from this source, and a tidal disruption event will be expected after 0.12 Myr.

Keywords: X-ray binary stars, Black holes, White dwarf stars, Gravitational wave sources, Stellar evolution
N-body Simulations of the Self-confinement of Viscous Self-gravitating Narrow Eccentric Planetary Ringlets. Narrow eccentric planetary ringlets have sharp edges, sizable eccentricity gradients, and a confinement mechanism that prevents radial spreading due to ring viscosity. Most proposed ringlet confinement mechanisms presume that there is one or more shepherd satellites whose gravitational perturbations keep the ringlet confined radially, but the absence of such shepherds in Cassini observations of Saturn's rings casts doubt upon those ringlet confinement mechanisms. The following uses a suite of N-body simulations to explore an alternate scenario, whereby ringlet self-gravity drives a narrow eccentric ringlet into a self-confining state. These simulations show that, under a wide variety of initial conditions, an eccentric ringlet's secular perturbations of itself causes the eccentricity of its outer edge to grow at the expense of its inner edge. This causes the ringlet's nonlinearity parameter q to grow over time until it exceeds the  q≃3/2  threshold where the ringlet's orbit-averaged angular momentum flux due to viscosity + self-gravity is zero. The absence of any net radial angular momentum transfer through the ringlet means that the ringlet has settled into a self-confining state, i.e., it does not spread radially due to its viscosity, and simulations also show that such ringlets have sharp edges. Nonetheless, viscosity still circularizes the ringlet in time τe ∼ 106 orbits ∼1000 yr, which will cause the ringlet's nonlinearity parameter to shrink below the  q≃3/2  threshold and allows radial spreading to resume. Either sharp-edged narrow eccentric ringlets are transient phenomena or exterior perturbations are also sustaining the ringlet's eccentricity. We then speculate about how such ringlets might come to be.

Keywords: Saturn, Solar system, Planetary rings, Orbital evolution, Planetary dynamics
Temporal Properties of Compressible Magnetohydrodynamic Turbulence. Describing the temporal properties of compressible magnetohydrodynamic (MHD) turbulence is a fundamental problem that has important implications for particle acceleration and transport in astrophysical plasmas. Here, by carefully analyzing the spatial and temporal properties of compressible MHD turbulence, we derive a new spectral power density function that is supported by simulations. This new function reveals that the low-frequency fluctuations are dominated by modes with small parallel wavenumbers with respect to the mean background magnetic field. Furthermore, for fluctuations with dynamically significant parallel wavenumbers, broadening around their eigenfrequencies is described by this function, which is in close agreement with simulations. We use this formalism to present the scaling properties of individual MHD modes. Such broadening is a direct consequence of nonlinear processes and is different for the three fundamental MHD modes. Our results provide a new window to investigate the temporal properties of turbulence and will enable further studies on the interaction between compressible MHD turbulence and energetic plasmas.

Keywords: Magnetohydrodynamical simulations, Astrophysical fluid dynamics, Plasma astrophysics
A Systematic Search for X-Ray Eclipse Events in Active Galactic Nuclei Observed by Swift. The nuclear regions of active galactic nuclei (AGNs) likely host clumpy clouds that occasionally obscure the central X-ray source, causing eclipse events. These events offer a unique opportunity to study the properties and origins of such clouds. However, these transient events are rarely reported due to the need for extensive, long-term X-ray monitoring for years. Here, we conduct a systematic search for eclipse events in 40 AGNs well monitored by the Swift X-ray Telescope over the past 20 yr, comprising a total of ∼11,000 observations. Our selection criteria rely on significant variations in X-ray flux and spectral shape. We identify three high-confidence events in three AGNs and eight candidates in six AGNs, all in Type I AGNs. The observed clouds have column densities of NH ∼ (0.2–31.2) × 1022 cm‑2 and ionization degrees of log ξ ∼ (‑1.3–2.2). For the five events with well-constrained duration, their distances from the central black hole range from (2.4 to 179) × 104 Rg, with two clouds near the dust sublimation zone, two farther out. Interestingly, we find tentative correlations between the cloud properties (i.e., ionization state and column density) and the black hole mass and mass-accretion rate, implying their strong connection to the accretion process, potentially via outflows. Our study also demonstrates the potential of the new X-ray all-sky monitor, the Einstein Probe, in providing more detection and physical constraints for such events.

Keywords: X-ray active galactic nuclei
An Analytical Model of Reconnection Rate in Electron-only Reconnection. Modeling the reconnection rate of collisionless electron-only reconnection presents a theoretical challenge. Unlike traditional magnetic reconnection with ion coupling, electron-only reconnection has a higher reconnection rate due to the magnetic flux being frozen in the electron flow, which is constrained by the electron-Alfvénic velocity rather than the ion-Alfvénic velocity. Recent observations have revealed that the electron-only reconnection rate is about 0.23, which is at the high end of the theoretical range, and the electron flow velocity in the outflow region falls significantly below the electron-Alfvénic velocity. Based on MHD and gyrokinetic theory, we propose a steady-state analytical model to calculate the reconnection rate in electron-only reconnection. Our model demonstrates that the electric field generated in the outflow direction by the decoupling between ions and electrons in the outflow region plays a crucial role in suppressing electron-only reconnection. The plasma beta value negatively affects the reconnection rate in electron-only reconnection, i.e., the larger the plasma beta, the smaller the reconnection rate. The analytical results of our model align well with the reconnection rates reported in previous studies.

Keywords: Space plasmas, Plasma astrophysics, Solar magnetic reconnection, Plasma physics
The Narrow Formation Pathway of Hot Saturns: Constraints on Initial Planetary Properties. The observed exoplanet population exhibits a scarcity of short-period Saturn-mass planets, a phenomenon referred to as the "hot-Saturn desert." This observational scarcity can be utilized to validate the theories regarding the formation and evolution of gas planets. In this study, we conduct large-scale numerical simulations to explore how the initial conditions of gas planets orbiting solar-type and M-dwarf stars influence their evolutionary trajectories in the semimajor axis versus planetary radius (a–R) parameter space. We generate a synthetic population of 10,000 short-period gaseous planets by systematically varying their initial planetary masses (Mp), initial planetary luminosities (Lp), initial core mass fractions ( fcore ), and semimajor axes (a). Furthermore, we assume these gaseous planets have ceased orbital migration and model their long-term thermal evolution, taking into account the impacts of atmospheric evaporation. Our results show that the initial Mp, Lp, and  fcore  are the dominant factors controlling radius evolution for short-period gas planets. The key to survival as a hot-Saturn analog appears to be having just the right combination of properties after gas disk dissipation: an Mp below 0.5 Jupiter mass (MJup), a substantial  fcore  of ≥30%, and relatively low Lp on the order of 10‑6 solar luminosity (L⊙) or less. The survival criteria for hot-Saturn analogs align with theoretically unfavorable initial conditions of gas planets formed via core accretion scenario, naturally explaining the observed boundaries of the hot-Saturn desert.

Keywords: Exoplanet evolution, Extrasolar gaseous planets, Exoplanets
A New Framework for Interstellar Medium Emission Line Models: Connecting Multiscale Simulations across Cosmological Volumes. The James Webb Space Telescope (JWST) and Atacama Large Millimeter/submillimeter Array have detected emission lines from the ionized interstellar medium (ISM) in some of the first galaxies at z ≳ 6. These measurements present an opportunity to better understand galaxy assembly histories and may allow important tests of state-of-the-art galaxy formation simulations. It is challenging, however, to model these lines in their proper cosmological context. In order to meet this challenge, we introduce a novel subgrid line emission modeling framework. The framework uses the high-z zoom-in simulation suite from the Feedback in Realistic Environments (FIRE) collaboration. The line emission signals from H II regions within each simulated FIRE galaxy are modeled using the semianalytic HIILINES code. A machine learning approach is then used to determine the conditional probability distribution for the line luminosity to stellar-mass ratio from the H II regions around each simulated stellar particle. This conditional probability distribution can then be applied to predict the line luminosities around stellar particles in lower-resolution, yet larger volume cosmological simulations. As an example, we apply this approach to the IllustrisTNG simulations at z = 6. The resulting predictions for the [O II], [O III], and Balmer line luminosities as a function of star formation rate agree well with current observations. Our predictions differ, however, from related works in the literature, which lack detailed subgrid ISM models. This highlights the importance of our multiscale simulation modeling framework. Finally, we provide forecasts for future line luminosity function measurements from the JWST and quantify the cosmic variance in such surveys.

Keywords: Interstellar line emission, High-redshift galaxies, Galaxy evolution
On the Broadening of the Characteristic Frequency Range toward Higher Photon Energies in the X-Ray Variability of the Black Hole Transient MAXI J1820+070. Energy-dependent X-ray power spectral states and band-limited noise (BLN) components have been seen in the low-hard state and intermediate states of black hole X-ray binaries. Here we report our analysis of Insight-HXMT observations of the black hole transient MAXI J1820+070 during its 2018 outburst when the source was brightest. We found opposite trends of low-frequency (&lt;0.1 Hz) and high-frequency (&gt;10 Hz) BLN components, i.e., decreasing versus increasing in frequency with increasing photon energy, respectively. This establishes an apparent two-way broadening of the power spectral plateau formed by multiple BLNs toward higher photon energies. The trend of the highest BLN component with increasing photon energy has been interpreted as indicating that the corresponding seed photons originated from a region relatively more central in the corona previously. The decreasing trend of the characteristic frequency of the lowest-frequency BLN component with increasing photon energy can then be interpreted as indicating that the corresponding seed photons originated from further out in the disk but on the opposite side of the central corona to the observer. These opposite trends then imply that the power spectral plateau represents the radial extension of the accretion disk that contributed the seed photons producing the BLNs, and show that the higher the photon energy is, the wider the plateau and the smaller the fractional variability. The plateau shows the analogy to the flat power spectrum with a low fractional variability of the power-law noise seen in the high-soft state, which corresponds to photons from the entire X-ray disk.

Keywords: Low-mass x-ray binary stars, X-ray binary stars, Stellar mass black holes
Deformation and Differential Rotation in Slowly Rotating Young Intermediate-mass Stars. Asteroseismology, the study of stellar vibrations, is a method that can probe the structure deformation and internal rotation of stars. Salient among the seismic inferences of rotation from TESS observations are TIC 408165734, whose equatorial rotation rate is 10% faster than the pole, and TIC 307930890, which has significant radial shear and shows a decreasing spin rate outward through its envelope. We also measure structural deformation in 15 stars, nine of which are oblate, a finding consistent with expectations for relatively fast-rotating nonmagnetic stars. The difference between polar and equatorial radii in TIC 47639058 is 130 times larger than that for the Sun. The remaining six stars display splittings consistent with a prolate shape (surprisingly), possibly indicating the presence of equatorial toroidal magnetic fields. These inferences provide constraints for numerical simulations and new insights to guide theories of δ Scuti structure and rotation.

Keywords: Delta Scuti variable stars
Electron-scale Magnetic Holes Generation Driven by Whistler-to-Bernstein Mode Conversion in Fully Kinetic Plasma Turbulence. Magnetic holes (MHs) are coherent structures characterized by a strong and localized magnetic field amplitude dip, commonly observed in the heliosphere. These structures come in different sizes, from magnetohydrodynamic to kinetic scales. Subion-scale MHs are usually sustained by an electron current vortex and exhibit a strong electron temperature anisotropy, with higher temperatures perpendicular to the background magnetic field. Magnetospheric multiscale observations (MMSs) have revealed electron-scale MHs to be ubiquitous in the turbulent Earth's magnetosheath and the solar wind, potentially playing an important role in the energy cascade and dissipation. Despite abundant observations, the origin of electron-scale MHs is still unclear and debated. In this work, we use fully kinetic simulations to investigate the role of plasma turbulence in generating electron-scale MHs. We find that the turbulence spontaneously produces electron-scale MHs via the following mechanism: first, large-scale turbulent velocity shears produce regions with high electron temperature anisotropy; these localized regions become unstable, generating oblique electron-scale whistler waves; as they propagate over the inhomogeneous turbulent background, whistler fluctuations develop an electrostatic component, turning into Bernstein-like modes; the strong electrostatic fluctuations produce current filaments that merge into an electron-scale current vortex; the resulting electron vortex locally reduces the magnetic field amplitude, finally evolving into an electron-scale MH. We show that MHs generated by this mechanism have properties consistent with MMSs and nontrivial kinetic features with a "mushroom"-shaped electron velocity distribution function. Our results have potential implications for understanding the formation and occurrence of electron-scale MHs in astrophysical turbulent and space environments, such as the Earth's magnetosheath and the solar wind.

Keywords: Interplanetary turbulence, Planetary magnetospheres, Solar wind