Sazuna/UAT_keywords huggingface dataset:
Observation-based Iterative Map for Solar Cycles. I. Nature of Solar Cycle Variability. Intercycle variations in the series of 11 yr solar activity cycles have a significant impact on both the space environment and climate. Whether solar cycle variability is dominated by deterministic chaos or stochastic perturbations remains an open question. Distinguishing between the two mechanisms is crucial for predicting solar cycles. Here we reduce the solar dynamo process responsible for the solar cycle to a one-dimensional iterative map, incorporating recent advances in the observed nonlinearity and stochasticity of the cycle. We demonstrate that deterministic chaos is absent in the nonlinear system, regardless of model parameters, if the generation of the poloidal field follows an increase-then-saturate pattern as the cycle strength increases. The synthesized solar cycles generated by the iterative map exhibit a probability density function (PDF) similar to that of observed normal cycles, supporting the dominant role of stochasticity in solar cycle variability. The parameters governing nonlinearity and stochasticity profoundly influence the PDF. The iterative map provides a quick and effective tool for predicting the range, including uncertainty, of the subsequent cycle strength when an ongoing cycle amplitude is known. Due to stochasticity, a solar cycle loses almost all its original information within one or two cycles. Although the simplicity of the iterative map, the behaviors it exhibits are generic for the nonlinear system. Our results provide guidelines for analyzing solar dynamo models in terms of chaos and stochasticity, highlight the limitations in predicting the solar cycle, and motivate further refinement of observational constraints on nonlinear and stochastic processes.

Keywords: Solar cycle, Solar magnetic fields, Solar active regions, Solar dynamo
The Origin of the Gas and Its Low Star Formation Efficiency in Quiescent Galaxies. Quiescent galaxies (QGs) typically have little cold gas to form stars. The discovery of gas-rich QGs challenges our conventional understanding of the evolutionary paths of galaxies. We take advantage of a new catalog of nearby massive galaxies with robust uniformly derived physical properties to better understand the origin of gas-rich QGs. We perform a comparative analysis of the cold interstellar medium and star formation properties of carefully matched samples of galaxies with varying degrees of star formation activity and gas richness. QGs with different gas content have virtually identical morphological type, light concentration, mass–size relation, stellar age, dark matter halo mass, and black hole activity. The only distinguishing characteristic is the environment. Gas-rich satellite QGs reside in a lower-density environment than their gas-poor counterparts, as a consequence of which they manage to retain their gas and experience a higher probability of cold-gas accretion or gas-rich mergers. The environmental densities of central QGs are similar regardless of their gas content. We suggest that the cold gas resides mainly in the outskirts of the gas-rich QGs, where bars, if present, cannot transport it inward efficiently to fuel central star formation. The prominent bulges in gas-rich QGs stabilize the cold gas from fragmentation and lead to low star formation efficiency.

Keywords: Star formation, Galaxy evolution, Interstellar medium
Destratification in the Progenitor Interior of the Mg-rich Supernova Remnant N49B. Simulations of presupernova evolution suggest that intense O-shell burning can be so active that, in extreme cases, it can merge with the outer C-burning shell, changing the initial conditions for the supernova explosion. However, such violent activity in the interior of stars has been difficult to confirm from observations of stars. Here we propose that the elemental composition of O-rich ejecta in supernova remnants (SNRs) can be a tool to test for this kind of intense shell burning activity in the final stages of progenitor evolution. As an example, we discuss the origin of "Mg-rich" ejecta in the SNR N49B. A high Mg/Ne mass ratio ≳ 1 suggests that the Ne- or O-burning shell has broken into or merged with the outer shell before the collapse. Such Mg-rich (or Ne-poor) ejecta has been identified in some other SNRs, supporting the idea that some destratification process, such as a shell merger, does indeed occur in the interiors of some massive stars, although they may not be the majority. Our results suggest that X-ray observations of O-rich ejecta in core-collapse SNRs will be a unique tool to probe the shell burning activity in the stellar interior during the final weeks to days of a massive star's evolution.

Keywords: X-ray astronomy, Stellar structures, Supernova dynamics, Core-collapse supernovae, Massive stars, Supernova remnants, Supernovae
Analyzing the Morphology of Late-phase Stellar Flares from G-, K-, and M-type Stars. Stellar flares occasionally present a peak-bump light-curve morphology, consisting of an initial impulsive phase followed by a gradual late phase. Analyzing this specific morphology can uncover the underlying physics of stellar flare dynamics, particularly the plasma heating–evaporation–condensation process. While previous studies have mainly examined peak-bump occurrences on M dwarfs, this report extends the investigation to G-, K-, and M-type stars. We utilize the flare catalog published by J. Crowley et al., encompassing 12,597 flares, detected by using Transiting Exoplanet Survey Satellite (TESS) observations. Our analysis identifies 10,142 flares with discernible classical and complex morphology, of which 197 (∼1.9%) exhibit the peak-bump feature. We delve into the statistical properties of these TESS late-phase flares, noting that both the amplitude and FWHM durations of both the peaks and bumps show positive correlations across all source-star spectral types, following a power law with indices 0.69 ± 0.09 and 1.0 ± 0.15, respectively. Additionally, a negative correlation between the flare amplitude and the effective temperature of their host stars is observed. Compared to the other flares in our sample, peak-bump flares tend to have larger and longer initial peak amplitudes and FWHM durations and possess energies ranging from 1031 to 1036 erg.

Keywords: Stellar flares, Stellar activity
Irradiated Atmospheres. III. Radiative-convective-mixing Equilibrium for Nongray Picket-fence Model. The nongray picket-fence model predicts more accurately the temperatures in low-density regions compared to semigray models. This study investigates how the vertical-mixing and convection fluxes modify the picket-fence model. The usual radiative-convective-equilibrium is now extended to radiative-convective-mixing-equilibrium. The temperature profile, characterized by an increase with pressure in the upper region and an inversion in the lower, is influenced by Rosseland opacity, spectral bands, and chemical composition. The atmosphere consists of five distinct layers: a pseudo-adiabatic zone shaped by mixing flux, two convective layers driven by convective flux with a smaller adiabatic gradient, and two radiative layers. In scenarios with lower Rosseland opacity, vertical mixing significantly reduces the width of temperature inversion, counteracting the cooling effect of the convective layers and driving the deep convective layer inward. The convective flux lowers the upper temperature and expands the upper convective layer. In the low-Rosseland-opacity five-band model, these fluxes significantly cool the midatmosphere when temperature increases with pressure, enlarging the pseudo-adiabatic region. Without TiO/VO, the pseudo-adiabatic region shrinks, indicating that TiO/VO enhances the mixing effect. Moreover, less mixing intensity is essential to maintain a stable five-layer structure. Therefore, future studies of chemical equilibrium with multifrequency atmospheric opacity should clearly define the constraints on vertical mixing.

Keywords: Radiative transfer simulations, Radiative transfer equation, Exoplanet atmospheres, Atmospheric structure
Exploring the Relationship between Stellar Mass, Metallicity, and Star Formation Rate at z ∼ 2.3 in KBSS-MOSFIRE. The metal enrichment of a galaxy is determined by the cycle of baryons in outflows, inflows, and star formation. The relative contribution and timescale of each process sets the relationship between stellar mass, metallicity, and the star formation rate (SFR). In the local Universe, galaxies evolve in an equilibrium state where the timescales on which SFR and metallicity vary are comparable, and they define a surface in mass─metallicity─SFR space known as the fundamental metallicity relation (FMR). However, high-redshift observations suggest that this state of equilibrium may not persist throughout cosmic time. Using galaxies from the Keck Baryonic Structure Survey (KBSS) observed with MOSFIRE, we explore the relationship between stellar mass, gas-phase oxygen abundance, and SFR at z ∼ 2.3. Across multiple strong-line calibrations and SFR calculation methods, KBSS galaxies are inconsistent with the locally defined FMR. We use both parametric and nonparametric methods of exploring a mass─metallicity─SFR relation. When using a parametric approach, we find no significant reduction mass─metallicity relation scatter when folding in SFR as a third parameter, although a nonparametric approach reveals that there could be a weak, redshift-dependent anticorrelation between residual gas-phase oxygen abundance and SFR. Injection-recovery tests show that a significant reduction in scatter requires a stronger anticorrelation between SFR and residual metallicity. Our results suggest that the local FMR may not persist to z ∼ 2.3, implying that z ∼ 2.3 galaxies at this redshift may not be in the equilibrium state described by the FMR and are more similar to higher-redshift galaxies.

Keywords: Galaxy properties, Galaxy chemical evolution, Scaling relations, Galaxy abundances, Galaxy evolution
Flipping of the Tidal Tails of the Ophiuchus Stream due to the Decelerating Galactic Bar. The Ophiuchus stellar stream presents a puzzle due to its complicated morphology, with a substructure perpendicular to the main track (spur), a broadened tail (fanning), and a shorter than expected angular extent given its old stellar population and short orbital period. The location of the stream approaches the Galactic center, implying a possible connection between its orbit and its unusual morphology. Here we demonstrate that the morphology of Ophiuchus can be attributed to its interaction with the decelerating Galactic bar, which leads to the flipping or transposition of its tidal tails. The short length of the stream is the result of stars stripped in the ancient past still remaining concentrated, and the spur, as well as the fanning, are composed of either leading or trailing tails built up of stars released at different time intervals. Our new spectroscopic data, obtained as part of the Southern Stellar Stream Spectroscopic Survey, and modeling of Ophiuchus indicate that, in the presence of the bar, an initial leading tail can be redistributed to the trailing side and vice versa, and the morphology of a stream can be reshaped. This result confirms that the Galactic bar plays a vital role in reconstructing the orbital behavior of streams passing close to the central region of the Milky Way.

Keywords: Globular star clusters, Stellar streams, Milky Way dynamics, Stellar dynamics, Milky Way Galaxy, Galactic bar
X-Raying CAMELS: Constraining Baryonic Feedback in the Circumgalactic Medium with the CAMELS Simulations and eRASS X-Ray Observations. The circumgalactic medium (CGM) around massive galaxies plays a crucial role in regulating star formation and feedback. Using the Cosmology and Astrophysics with MachinE Learning Simulations (CAMELS) suite, we develop emulators for the X-ray surface brightness profile and the X-ray luminosity–stellar mass scaling relation, to investigate how stellar and active galactic nucleus (AGN) feedback shape the X-ray properties of the hot CGM. Our analysis shows that at CGM scales (1012 ≲ Mhalo/M⊙ ≲ 1013, 10 ≲ r kpc‑1 ≲ 400), stellar feedback more significantly impacts the X-ray properties than AGN feedback within the parameters studied. Comparing the emulators to recent eROSITA All Sky Survey (eRASS) observations, it is found that stronger feedback than is currently implemented in the IllustrisTNG, SIMBA, and Astrid simulations is required to match the observed CGM properties. However, adopting these enhanced feedback parameters causes deviations in the stellar mass–halo mass relations from observational constraints below the group-mass scale. This tension suggests possible unaccounted-for systematics in X-ray CGM observations or inadequacies in the feedback models of cosmological simulations.

Keywords: X-ray astronomy, Hydrodynamical simulations, Galactic and extragalactic astronomy, Circumgalactic medium
Cloud Properties in Simulated Galactic Winds. In this work, we investigate the properties of a population of cool clouds in simulated galaxy outflows. Using data from the Cholla Galactic OutfLow Simulations (or CGOLS) isolated galaxy simulations, we generate catalogs of ∼105 clouds. We describe the impact of two different supernova feedback models—a centrally concentrated starburst and disk-wide distributed star formation—on the resulting cloud population. In both cases we find that the mass distribution function dN/dM ∝ M−2, in good agreement with model predictions of turbulent fragmentation. We explore how cloud properties change with distance from the galaxy and find no qualitative distinction between the two feedback modes, although significant quantitative differences exist in attributes such as the total number of clouds, their densities, etc. We further show that both internal cloud velocities and cloud─cloud relative velocities are described well by properties of turbulent motion, despite significant bulk radial velocities. Finally, we investigate the distribution of cloud sizes in the context of recent theoretical arguments about cloud survival in winds. We find that the proposed cloud survival criteria are a good predictor of cloud survival, in both the case where clouds are primarily destroyed and the case where cloud growth occurs in the outflow.

Keywords: Starburst galaxies, Hydrodynamical simulations, Galactic winds, Astronomical simulations, High-velocity clouds, Galaxies
On the External Inverse Compton Scattering off the Prompt Emission in GRB 221009A. The temporal evolution of the TeV emission of GRB 221009A displays a smooth transition from an initial rapid rise to a slower rise and eventually a decay phase. The smooth light curve suggests an afterglow origin of the TeV emission. The temporal overlap between the prompt keV–MeV emission and the early TeV afterglow indicates that external inverse Compton (EIC) scattering between the prompt keV–MeV photons and the afterglow electrons is inevitable. Since the energy density of the prompt emission is much higher than that of the afterglow during the early phase, the EIC process dominates the cooling of afterglow electrons. The EIC scattering rate is influenced by the anisotropy of the seed photon field, which depends on the radius of the internal dissipation (Rdis), where the prompt emission is produced, and that of the external shock (Rext), where the afterglow emission is produced. We investigate the EIC process for different values of Rdis/Rext and find that the EIC scattering rate can differ by a factor of ∼2 accordingly. For GRB 221009A, the EIC emission dominates during the early rising phase of the TeV afterglow. It then transitions to a phase dominated by the synchrotron self-Compton emission as the intensity of the prompt emission decreases. Additionally, we investigate the effect of γγ absorption in the TeV afterglow by prompt MeV photons and find it insufficient to explain the early rapid rise in the TeV afterglow.

Keywords: Gamma-ray bursts, Non-thermal radiation sources, Radiative processes
Photometric Objects Around Cosmic Webs (PAC). VII. Disentangling Mass and Environment Quenching with the Aid of Galaxy–Halo Connection in Simulations. Star formation quenching in galaxies plays a crucial role in galaxy evolution and is believed to be driven primarily by galaxy mass and environment. However, disentangling these effects is difficult because galaxy mass and environment are strongly correlated. In Paper V, we addressed this challenge using the Photometric Objects Around Cosmic Webs method, which integrates spectroscopic and deep photometric surveys. This approach enabled us to measure the excess surface density   of blue and red galaxies surrounding massive central galaxies down to 109.0M⊙. Despite this, fully separating mass and environmental effects remains challenging due to the difficulty in identifying a complete sample of low-mass central galaxies in redshift space. To overcome this, we derive the average quenched fraction of central galaxies,  , by combining the reconstructed 3D quenched fraction distribution  , the stellar mass-halo mass relation in simulations, and the observed total quenched fraction,  . With  ,   and the galaxy–halo connection, we assign a quenched probability to each (sub)halo and analyze galaxy quenching comprehensively. Our findings indicate that mass quenching dominates, with the mass-quenched fraction increasing from 0.3 to 0.87 across the stellar mass range [109.5, 1011.0]M⊙, while environmental quenching decreases from 0.17 to 0.03. Furthermore, more massive host halos are more effective at quenching their satellite galaxies, whereas satellite stellar mass has a minimal impact on environmental quenching. Within the studied stellar mass range, TNG300-1 exhibits lower mass-quenching efficiency but higher environmental-quenching compared to observations.

Keywords: Galaxy quenching, Galaxy formation, Galaxy evolution
LAMOST Young Stellar Objects. I. Spectroscopically Identifying and Characterizing M-type YSOs. This study utilized Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) low-resolution spectra to identify M-type young stellar objects (YSOs) and characterize their accretion signatures. We measured characteristic features, including hydrogen Balmer, Li I, He I, Na I, and Ca II lines, as well as molecular absorption bands such as CaH. These features were evaluated for their potential to distinguish between different classes of M-type stars. In addition to the commonly used Hα emission and Li I λ6708 absorption, other features such as He I, Na I, Ca II HK and infrared triplet (IRT) lines, and CN, CaH, and VO bands also show potential for identifying YSOs from M-type dwarfs and giants. Based on key red-band features, we identified over 8500 M-type YSO candidates from the LAMOST DR8 archive using the random forest technique, with over 2300 of them likely being classical T Tauri stars (CTTSs). By incorporating Gaia astrometry, Two Micron All Sky Survey photometry, and extinction from 3D dust maps, we estimated the basic properties (such as age and mass) of the YSO candidates based on PARSEC models. We also estimated the mass accretion rates of the CTTS candidates using Hα emission. The derived accretion rates show a dependence on age and mass similar to that described in previous studies. Significant scatter in mass accretion rates exists even among stars with a similar age and mass, which may be partly attributed to variations in Hα emission and the veiling.

Keywords: Late-type stars, T Tauri stars, Young stellar objects, Stellar accretion, Stellar spectral lines
SF-R You Sure? The Conflicting Role of Star Formation Rates in Constraining the Evolution of Milky Way Analogs in Cosmological Simulations. Milky Way analogs (MWAs) have long been studied by astronomers to place our Galaxy within an extragalactic context. With the power of cosmological simulations, we are now able to not only characterize MWAs today, but also watch as they evolve through cosmic time. We use the Evolution and Assembly of GaLaxies and their Environments (EAGLE) and Illustris The Next Generation (IllustrisTNG) simulations to study a group of MWAs defined by their stellar mass (SM) and star formation rate (SFR). We trace these galaxies back along their evolution to investigate the star-forming and mass assembly tracks taken by a galaxy to become an MWA today in light of these chosen parameters. We also take mock-observations of "MWAs" at z &gt; 0 and trace them forward in time to determine if galaxies that looked similar to the Milky Way earlier in their evolution still look like the Milky Way today, thus quantifying a selection efficiency that could inform future observational studies of MWAs. We find that most galaxies with Milky Way–SM follow a similar evolution regardless of present-day SFR, although MWAs in IllustrisTNG generally have not quenched, leading to star formation histories that produce "too-blue" galaxies today. Additionally, we find contamination by MWA-"imposters" in our mock-observations, with low selection efficiency at high redshift due to the tight constraint requiring convergence to the Milky Way's present-day SFR. Our work suggests present-day SM may suffice as a stand-alone selection parameter and helps to clarify how MWAs should be selected, and thus will be an important reference for future studies of both simulated and observed MWAs.

Keywords: Hydrodynamical simulations, Theoretical techniques, Milky Way Galaxy physics, Galaxy evolution, Milky Way evolution, Milky Way Galaxy
Late-time HST and JWST Observations of GRB 221009A: Evidence for a Break in the Light Curve at 50 days. GRB 221009A is one of the brightest transients ever observed, with the highest peak gamma-ray flux for a gamma-ray burst (GRB). A Type Ic-BL supernova (SN), SN 2022xiw, was definitively detected in late-time JWST spectroscopy (t = 195 days, observer frame). However, photometric studies have found SN 2022xiw to be less luminous (10%‑70%) than the canonical GRB-SN, SN 1998bw. We present late-time Hubble Space Telescope (HST)/WFC3 and JWST/NIRCam imaging of the afterglow and host galaxy of GRB 221009A at t ∼185, 277, and 345 days post-trigger. Our joint archival ground, HST, and JWST light-curve fits show strong support for a break in the light-curve decay slope at t = 50 ± 10 days (observer frame) and a SN at &lt;1.5× the optical/near-IR flux of SN 1998bw. This break is consistent with an interpretation as a jet break when requiring slow-cooling electrons in a wind medium with an electron energy spectral index p &gt; 2 and νm &lt; νc. Our light curves and joint HST/JWST spectral energy distribution (SED) also show evidence for the late-time emergence of a bluer component in addition to the fading afterglow and SN. We find consistency with the interpretations that this source is either a young, massive, low-metallicity star cluster or a scattered-light echo of the afterglow with a SED shape of fν ∝ ν2.0±1.0.

Keywords: Gamma-ray bursts, High energy astrophysics, Core-collapse supernovae, Hubble Space Telescope, HST photometry, James Webb Space Telescope, Supernovae