Sazuna/UAT_keywords huggingface dataset:
Violent Starbursts and Quiescence Induced by Far-ultraviolet Radiation Feedback in Metal-poor Galaxies at High Redshift. JWST observations of galaxies at z ≳ 8 suggest that they are more luminous and clumpier than predicted by most models, prompting several proposals on the physics of star formation and feedback in the first galaxies. In this paper, we focus on the role of ultraviolet (UV) radiation in regulating star formation by performing a set of cosmological radiation hydrodynamics simulations of one galaxy at subparsec resolution with different radiative feedback models. We find that the suppression of cooling by far-UV (FUV) radiation (i.e., H2 dissociating radiation) from Population II stars is the main physical process triggering the formation of compact and massive star clusters and is responsible for the bursty star formation observed in metal-poor galaxies at z ≳ 10. Indeed, artificially suppressing FUV radiation leads to a less intense continuous mode of star formation distributed into numerous but low-mass open star clusters. Due to the intense FUV field, low-metallicity clouds remain warm (∼104 K) until they reach a relatively high density (≳103 cm‑3), before becoming self-shielded and transitioning to a colder (∼100 K), partially molecular phase. As a result, star formation is delayed until the clouds accumulate enough mass to become gravitationally unstable. At this point, the clouds undergo rapid star formation, converting gas into stars with high efficiency. We therefore observe exceptionally bright galaxies (10 times brighter than for continuous star formation) and subsequent quenched "dead" galaxies that did not form stars for tens of Myr.

Keywords: Primordial galaxies, High-redshift galaxies
Convective Overstability in Radially Global Protoplanetary Disks. I. Pure Gas Dynamics. Protoplanetary disks are prone to several hydrodynamic instabilities. One candidate, convective overstability (COS), can drive radial semiconvection that may influence dust dynamics and planetesimal formation. However, the COS has primarily been studied in local models. This paper investigates the COS near the midplane of radially global disk models. We first conduct a global linear stability analysis, which shows that linear COS modes exist only radially inward of their Lindblad resonance (LR). The fastest-growing modes have LRs near the inner radial domain boundary with effective radial wavelengths that can be a substantial fraction of the disk radius. We then perform axisymmetric global simulations and find that the COS's nonlinear saturation is similar to previous incompressible shearing box simulations. In particular, we observe the onset of persistent zonal and elevator flows for sufficiently steep radial entropy gradients. In full 3D, nonaxisymmetric global simulations, we find the COS produces large-scale, long-lived vortices, which induce the outward radial transport of angular momentum via the excitation of spiral density waves. The corresponding α-viscosity values of order 10‑3 agree well with those found in previous 3D compressible shearing box simulations. However, in global disks, significant modifications to their radial structure are found, including the formation of pressure bumps. Interestingly, the COS typically generates an outward radial mass transport, i.e., decretion. We briefly discuss the possible implications of our results for planetesimal formation and for interpreting dust rings and asymmetries observed in protoplanetary disks.

Keywords: Hydrodynamics, Protoplanetary disks, Planetesimals, Astrophysical fluid dynamics, Planet formation
Effect of Magnetic Diffusion in the Chromosphere on the Solar Wind. We investigate nonideal magnetohydrodynamical (MHD) effects in the chromosphere on the solar wind by performing MHD simulations for Alfvén-wave-driven winds, explicitly including ohmic and ambipolar diffusion. We find that MHD waves are significantly damped in the chromosphere by ambipolar diffusion so that the Alfvénic Poynting flux that reaches the corona is substantially reduced. As a result, the coronal temperature and the mass-loss rate of the solar wind are considerably reduced, compared with those obtained from an ideal MHD case, which is indicative of the great importance of the nonideal MHD effects in the solar atmosphere. However, the temperature and the mass-loss rate are recovered by a small increase in the convection-originated velocity perturbation at the photosphere because of the sensitive dependence of the ambipolar diffusion and reflection of Alfvén waves on the physical properties of the chromosphere. We also find that density perturbations in the corona are reduced by the ambipolar diffusion of Alfvén waves in the chromosphere because the nonlinear generation of compressible perturbations is suppressed.

Keywords: Stellar winds, Solar wind, Alfven waves, Magnetohydrodynamical simulations
Study of Particle Acceleration Using Fine Structures and Oscillations in Microwaves from the Electron Cyclotron Maser. The accelerated electrons during solar flares produce radio bursts and nonthermal X-ray signatures. The quasi-periodic pulsations (QPPs) and fine structures in spatial–spectral–temporal space in radio bursts depend on the emission mechanism and the local conditions, such as magnetic fields, electron density, and pitch-angle distribution. Radio burst observations with high-frequency time resolution imaging provide excellent diagnostics. In converging magnetic field geometries, the radio bursts can be produced via the electron cyclotron maser (ECM). Recently, using observations made by the Karl G. Jansky Very Large Array (VLA) at 1–2 GHz, Yu et al. reported a discovery of long-lasting auroral-like radio bursts persistent over a sunspot and interpreted them as ECM-generated emission. Here we investigate the detailed second and subsecond temporal variability of this continuous ECM source. We study the association of 5 s period QPPs with a concurrent GOES C1.5-class flare, utilizing VLA's imaging spectroscopy capability with an extremely high temporal resolution (50 ms). We use the density and magnetic field extrapolation model to constrain the ECM emission to the second harmonic O-mode. Using the delay of QPPs from X-ray emission times, combined with X-ray spectroscopy and magnetic extrapolation, we constrain the energies and pitch angles of the ECM-emitting electrons to ≈4–8 keV and &gt;26°. Our analysis shows that the loss-cone diffusion continuously fuels the ECM via Coulomb collisions and magnetic turbulence between a length scale of 5 and 100 Mm. We conclude that the QPP occurs via the Lotka–Volterra system, where the electrons from solar flares saturate the continuously operating ECM and cause temporary oscillations.

Keywords: Solar oscillations, Solar active region magnetic fields, Solar radio emission
Geometry, Dissipation, Cooling, and the Dynamical Evolution of Wind-blown Bubbles. Bubbles driven by energy and mass injection from small scales are ubiquitous in astrophysical fluid systems and essential to feedback across multiple scales. In particular, O stars in young clusters produce high-velocity winds that create hot bubbles in the surrounding gas. We demonstrate that the dynamical evolution of these bubbles is critically dependent upon the geometry of their interfaces with their surroundings and the nature of heat transport across these interfaces. These factors together determine the amount of energy that can be lost from the interior through cooling at the interface, which in turn determines the ability of the bubble to do work on its surroundings. We further demonstrate that the scales relevant to physical dissipation across this interface are extremely difficult to resolve in global numerical simulations of bubbles for parameter values of interest. This means the dissipation driving evolution of these bubbles in numerical simulations is often of a numerical nature. We describe the physical and numerical principles that determine the level of dissipation in these simulations; we use this, along with a fractal model for the geometry of the interfaces, to explain differences in convergence behavior between hydrodynamical and magnetohydrodynamical simulations presented here. We additionally derive an expression for momentum as a function of bubble radius expected when the relevant dissipative scales are resolved and show that it still results in efficiently cooled solutions, as postulated in previous work.

Keywords: Stellar feedback, Stellar wind bubbles, Star forming regions, Young star clusters, Stellar winds, Interstellar medium
Statistics for Galaxy Outflows at z ∼ 6–9 with Imaging and Spectroscopic Signatures Identified with JWST/NIRCam and NIRSpec Data. We present statistics of z ∼ 6–9 galaxy outflows indicated by spatially extended gas emission and broad lines. With a total of 61 spectroscopically confirmed galaxies at z ∼ 6–9 in the JWST CEERS, GLASS, and ERO data, we find four galaxies with [O III] + Hβ ionized gas emission significantly extended beyond the kiloparsec-scale stellar components on the basis of the emission line images constructed by the subtraction of NIRCam broadband (line on/off-band) images. By comparison with low-z galaxies, the fraction of galaxies with spatially extended gas, 4/18, at z ∼ 6–9 is an order of magnitude higher than that at z ∼ 0–1, which can be explained by events triggered by frequent major mergers at high redshift. We also investigate medium- and high-resolution NIRSpec spectra of 30 galaxies at z ∼ 6–9, and identify five galaxies with broad (140‑800 km s‑1) lines in the [O III] forbidden line emission, suggestive of galaxy outflows. One galaxy at z = 6.38 shows both spatially extended gas emission and the broad lines, while none of the galaxies with spatially extended gas emission or broad lines present a clear signature of active galactic nuclei (AGN) in either the line diagnostics or type 1 AGN line broadening (&gt;1000 km s‑1), which suggests that outflows are mainly driven by stellar feedback. The existence of galaxies with/without spatially extended gas emission or broad lines may be explained by different viewing angles toward outflows or the fact that these are galaxies in the early, late, or post phases of galaxy outflows at high redshift, where relatively large fractions of such galaxies indicate longer-duration and/or more frequent outflows at early cosmic epochs.

Keywords: Galaxy formation, Galaxy evolution, Circumgalactic medium
Controls of Atmospheric Methane on Early Earth and Inhabited Earth-like Terrestrial Exoplanets. Methane (CH4) is a primarily biogenic greenhouse gas. As such, it represents an essential biosignature to search for life on exoplanets. Atmospheric CH4 abundance on Earth-like inhabited exoplanets is likely controlled by marine biogenic production and atmospheric photochemical consumption. Such interactions have been previously examined for the case of the early Earth where primitive marine ecosystems supplied CH4 to the atmosphere, showing that the atmospheric CH4 response to biogenic CH4 flux variations is nonlinear, a critical property when assessing CH4 reliability as a biosignature. However, the contributions of atmospheric photochemistry, metabolic reactions, or solar irradiance to this nonlinear response are not well understood. Using an atmospheric photochemical model and a marine microbial ecosystem model, we show that the production of hydroxyl radicals from water vapor photodissociation is a critical factor controlling the atmospheric CH4 abundance. Consequently, atmospheric CH4 partial pressure (pCH4) on inhabited Earth-like exoplanets orbiting Sun-like stars (F-, G-, and K-type stars) would be controlled primarily by stellar irradiance. Specifically, irradiance at wavelengths of approximately 200–210 nm is a major controlling factor for atmospheric pCH4 when the carbon dioxide partial pressure is sufficiently high to absorb most stellar irradiance at 170–200 nm. Finally, we also demonstrated that inhabited exoplanets orbiting near the outer edge of K-type stars' habitable zones are better suited for atmospheric pCH4 buildup. Such properties will provide valuable support for future detection of life signatures.

Keywords: Atmospheric composition, Exoplanet atmospheric composition , Astrobiology, Earth atmosphere
Solar Flare Ribbon Fronts. II. Evolution of Heating Rates in Individual Flare Footpoints. Solar flare ribbon fronts appear ahead of the bright structures that normally characterize solar flares, and can persist for an extended period of time in spatially localized patches before transitioning to "regular" bright ribbons. They likely represent the initial onset of flare energy deposition into the chromosphere. Chromospheric spectra (e.g., He I 10830 Å and the Mg II near-UV lines) from ribbon fronts exhibit properties rather different to typical flare behavior. In prior numerical modeling efforts we were unable to reproduce the long lifetime of ribbon fronts. Here we present a series of numerical experiments that are rather simple but which have important implications. We inject a very low flux of nonthermal electrons (F = 5 × 108 erg s‑1 cm‑2) into the chromosphere for 100 s before ramping up to standard flare energy fluxes (F = 1010‑11 erg s‑1 cm‑2). Synthetic spectra not only sustained their ribbon-front-like properties for significantly longer: in the case of harder nonthermal electron spectra, the ribbon front behavior persisted for the entirety of this weak-heating phase. Lengthening or shortening the duration of the weak-heating phase commensurately lengthened or shortened the ribbon front lifetimes. Ribbon fronts transitioned to regular bright ribbons when the upper chromosphere became sufficiently hot and dense, which happened faster for softer nonthermal electron spectra. Thus, the lifetime of flare ribbon fronts are a direct measure of the duration over which a relatively low flux of high-energy electrons precipitates to the chromosphere prior to the bombardment of a much larger energy flux.

Keywords: Hydrodynamical simulations, Solar flares, Solar flare spectra, Radiative transfer, Solar chromosphere
Advancing Precision Particle Background Estimation for Future X-Ray Missions: Correlated Variability between the Alpha Magnetic Spectrometer and Chandra/XMM-Newton. Galactic cosmic-ray (GCR) particles have a significant impact on the particle-induced background of X-ray observatories, and their flux exhibits substantial temporal variability, potentially influencing background levels. In this study, we present 1 day binned high-energy reject rates derived from the Chandra-ACIS and XMM-Newton EPIC-pn instruments, serving as proxies for the GCR particle flux. We systematically analyze the ACIS and EPIC-pn reject rates and compare them with the AMS proton flux. Our analysis initially reveals robust correlations between the AMS proton flux and the ACIS/EPIC-pn reject rates when binned over 27 day intervals. However, a closer examination reveals substantial fluctuations within each 27 day bin, indicating shorter-term variability. Upon daily binning, we observe finer temporal structures in the data sets, demonstrating the presence of recurrent variations with periods of ∼25 days and 23 days in the ACIS and EPIC-pn reject rates, respectively, spanning the years 2014–2018. Notably, during the 2016–2017 period, we additionally detect periodicities of ∼13.5 days and 9 days in the ACIS and EPIC-pn reject rates, respectively. Intriguingly, we observe a time lag of ∼6 days between the AMS proton flux and the ACIS/EPIC-pn reject rates during the second half of 2016. This time lag is not visible before 2016 and after 2017. The underlying physical mechanisms responsible for this time lag remain a subject of ongoing investigation.

Keywords: Galactic cosmic rays
Hyperfine Structure Investigation of Singly Ionized Thulium in Fourier-transform Spectra. The hyperfine structure of 40 spectral lines of singly ionized thulium (Tm II) in emission spectra from a hollow cathode discharge lamp measured with a Fourier transform spectrometer in the wavelength range from 335 to 2345 nm has been investigated. As a result of the analysis, the magnetic dipole hyperfine structure constants A for 27 fine structure levels of Tm II were determined for the first time. In addition, the values of two magnetic dipole hyperfine structure constants A from the literature were declared incorrect, and the corrected values were given.

Keywords: Solar abundances, Atomic spectroscopy, Atomic data
The Stagger Code for Accurate and Efficient, Radiation-coupled Magnetohydrodynamic Simulations. We describe the Stagger code for simulations of magnetohydrodynamic (MHD) systems. This is a modular code with a variety of physics modules that will let the user run simulations of deep stellar atmospheres, sunspot formation, stellar chromospheres and coronae, proto-stellar disks, star formation from giant molecular clouds, and even galaxy formation. The Stagger code is efficiently and highly parallelizable, enabling such simulations with large ranges of both spatial and temporal scales. We describe the methodology of the code and present the most important of the physics modules, as well as its input and output variables. We show results of a number of standard MHD tests to enable comparison with other, similar codes. In addition, we provide an overview of tests that have been carried out against solar observations, ranging from spectral line shapes, spectral flux distribution, limb darkening, intensity and velocity distributions of granulation, to seismic power spectra and the excitation of p-modes. The Stagger code has proven to be a high-fidelity code with a large range of uses.

Keywords: Computational methods, Radiative magnetohydrodynamics, Atomic physics
Asymmetry, Gap Opening, and a High Accretion Rate on DM Tau: A Hypothesis Based on the Interaction of Magnetized Disk Wind with Planets. Over 200 protoplanetary disk systems have been resolved by the Atacama Large Millimeter/submillimeter Array (ALMA), and the vast majority suggest the presence of planets. The dust gaps in transition disks are considered evidence of giant planets sculpting gas and dust under appropriate disk viscosity. However, the unusually high accretion rates in many T Tauri stars hosting transition disks challenge this theory. As the only disk currently observed with high turbulence, the high accretion rate (∼10‑8.3 M ⊙ yr‑1) observed in DM Tau indicates the presence of strong turbulence within the system. Considering the recent theoretical advancements in magnetized disk winds are challenging the traditional gap-opening theories and viscosity-driven accretion models, our study presents a pioneering simulation incorporating a simplified magnetized disk wind model to explain the observed features in DM Tau. Employing multifluid simulations with an embedded medium mass planet, we successfully replicate the gap formation and asymmetric structures evident in ALMA Band 6 and the recent Karl G. Jansky Very Large Array 7 mm observations. Our results suggest that when magnetized disk wind dominates the accretion mode of the system, it is entirely possible for a planet with a medium mass to exist within the gap inside 20 au of DM Tau. This means that DM Tau may not be as turbulent as imagined. However, viscosity within the disk should also contribute a little turbulence to maintain disk stability.

Keywords: Planet formation, Astrophysical fluid dynamics, Protoplanetary disks, Hydrodynamics
Millimeter to THz Spectroscopy of HC<SUP>18</SUP>O<SUP>+</SUP> and HC<SUP>17</SUP>O<SUP>+</SUP>: Accurate Rest Frequencies for Astrophysical Studies. Heavy oxygen isotopic species of HCO+ are important optically thin astrophysical tracers. The ground-state rotational spectrum of HC18O+, DC18O+, HC17O+, and DC17O+ has been recorded in the laboratory in the frequency range from 85 GHz to 1.3 THz. The ions have been produced in the negative column of a glow-discharge plasma, and their spectrum has been recorded in absorption using a frequency-modulation submillimeter-wave spectrometer. Various sources of systematic error have been carefully accounted for in order to obtain highly accurate line-position measurements. Theoretical estimates of the molecular parameters and of the collision effects on the line shape have been obtained by high-level ab initio calculations. The analysis yielded much improved rotational and centrifugal distortion constants, thus bringing the spectroscopic characterization of these rare isotopic variants to the same level of the parent species. Also, the first experimental rotational data for DC17O+ have been provided. These results allow for the calculation of an updated set of rest frequencies to support current and future astrophysical studies. The derived data set for the widely used HC18O+ tracer reaches an accuracy of a few parts in 109 up to 1.5 THz. Such accuracy is important for the analysis of astrophysical objects targeted by Atacama Large Millimeter/submillimeter Array observations at the submillimeter regime.

Keywords: Collisional broadening, Spectral line lists, Laboratory astrophysics
Constraints from Parallaxes and Average Period Spacings in the Asteroseismic Study of Eight Hydrogen-atmosphere Pulsating White Dwarfs. With space missions such as Kepler, TESS, and Gaia, we have a wealth of data on pulsating white dwarfs that can be leveraged in white dwarf asteroseismology. We address the question of the proportion of white dwarfs with thin hydrogen layers versus those with thick hydrogen layers. We also provide a mass–radius relation for carbon–oxygen-core, hydrogen-atmosphere white dwarfs. Such a relationship can be used in conjunction with magnitudes and distance measurements to constrain the mass and effective temperature of the white dwarfs. We select nine hydrogen-atmosphere pulsating white dwarfs for their rich pulsation spectra. From such pulsation spectra, we can derive the asymptotic period spacing, which in turn allows us to determine the thickness of the hydrogen and helium envelope of the models, without having to perform period-by-period fitting. We find that the majority of the white dwarfs have thicker hydrogen layers and we determine an upper limit of M  r  = 1–10‑2.2 for the location of the base of the helium layer, in accordance with stellar evolution models. We confirm a finding from earlier studies that used a mass–radius relation and Gaia data to determine the effective temperatures of white dwarfs. The Gaia data systematically point to white dwarfs of lower effective temperature than indicated by the spectroscopy. Our results also support the hypothesis that white dwarfs with thicker hydrogen layers are more common than those with thinner layers.

Keywords: Stellar interiors, Periodic variable stars, White dwarf stars, Stellar astronomy, DA stars, Compact objects, Stellar oscillations, Asteroseismology