Sazuna/UAT_keywords huggingface dataset:
The Role of Environment in Triggering Active Galactic Nuclei—Evidence for a Change at z ∼ 1. What triggers active galactic nuclei (AGN) in some galaxies and what role this brief period of activity plays in the overall evolution of galaxies are still open questions. This paper explores whether or not the local, on scales of ≍1 Mpc, galaxy density plays a role in triggering AGN when controlling for stellar mass. We consider this question as a function of redshift and AGN selection in the X-ray versus in the IR. We use available density maps within 4.8 deg2 of the XMM-Large Scale Structure (XMM-LSS) field in the redshift range 0.1 &lt; z &lt; 1.6. Our key result is that the environment may play a role in triggering IR AGN. In particular, at z &gt; 1.2, the incidence of AGN increases in higher-density environments, controlling for stellar mass. However, this dependence reverses at z &lt; 1.2, where the incidence of IR AGN is higher in lower-density environments. By contrast, among X-ray-selected AGN, there is no significant local density dependence. Bootstrapping analysis confirms these conclusions. While these results agree with previous work on both obscured and unobscured AGN, this is the first study to use a consistent methodology across IR and X-ray samples, as well as study IR dependence in this full redshift range. Upcoming large spectroscopic surveys such as the Prime Focus Spectrograph Galaxy Evolution Survey will be critical in further elucidating how the environment affects AGN triggering across different cosmic epochs.

Keywords: X-ray active galactic nuclei
A Near-infrared Spectral Library of Very Young Brown Dwarfs and Planetary Mass Objects in the Orion Nebula Cluster. Age-benchmark brown dwarf and planetary-mass-object spectroscopy is key to characterizing substellar evolution. In this paper, we present the JHK medium-resolution (R ∼ 3000) spectra of 25 7─76 MJup (spectral types L3.0─M6.0) brown dwarfs and planetary mass objects in the Orion Nebula Cluster, obtained with MOSFIRE installed at the W. M. Keck I telescope. We obtained the spectral types of the targets in our sample using template brown dwarf and planetary-mass-object spectra. We confirmed their extreme youth (&lt;5 Myr) and membership of the cluster using spectral indices as well as the diversity of their spectra, even for targets with similar spectral types. Six of our targets presented Paschen β and Brackett γ emission lines, suggesting the existence of accreting protoplanetary disks for objects with masses as low as 7 MJup. After analyzing the emission lines of those objects, and measuring their accretion rates, we compared them to those of stars, brown dwarfs, and planetary mass objects, confirming that planetary mass young objects deplete their disks quickly at young ages. Finally, we illustrate the spectral evolution of a 7─10 MJup planetary mass object through its life from 1─3 to 200 Myr old, using one of our latest spectral type targets and other targets from the literature with older ages but similar estimated masses. The spectra are publicly available for the community's use as data behind the figures.

Keywords: Open star clusters, Young star clusters, L dwarfs
Fe Abundances of Early Galaxies at z = 9─12 Derived with Deep JWST Spectra. We derive Fe abundance ratios of seven galaxies at z = 9─12 with −22 &lt; MUV &lt; −19 whose JWST/NIRSpec spectra achieve very high signal-to-noise ratios, S/N = 60─320, at rest-frame UV wavelength. We fit stellar population synthesis model spectra to these JWST spectra, masking out nebular emission lines, and obtain Fe abundance ratios of [Fe/H] = −1─0 dex for five galaxies and upper limits of [Fe/H] ∼ −2─0 dex for two galaxies. We compare these [Fe/H] values with the oxygen abundances of these galaxies ( 7.4&lt;12+log(O/H)&lt;8.4 ) in the same manner as previous studies of z ∼ 2─6 galaxies, and derive oxygen-to-iron abundance ratios [O/Fe]. We find that two out of seven galaxies, GS-z11-0 and GN-z11, show Fe enhancements relative to O ([O/Fe] &lt; 0 dex), especially GS-z11-0 (z = 11.12) with an Fe enhancement ( [O/Fe]=−0.68−0.55+0.37  dex) beyond the solar abundance ratio at ∼2σ. Because, unlike GS-z11-0, GN-z11 (z = 10.60) may host an active galactic nucleus (AGN), we constrain [O/Fe] via Fe II emission under the assumption of an AGN and confirm that the Fe enhancement is consistent even in this case. While the [O/Fe] values of most galaxies are comparable to those of core-collapse supernovae (CCSNe) yields, the Fe enhancements of GS-z11-0 and GN-z11 are puzzling. We develop chemical evolution models, and find that the Fe enhancements in GS-z11-0 and GN-z11 can be explained by either (1) pair-instability supernovae or bright hypernovae with little contribution from CCSNe, or (2) Type Ia supernovae with short delay times (∼30─50 Myr) and top-light initial mass functions.

Keywords: Galaxy formation, Galaxy chemical evolution, Star formation, Galaxy evolution, High-redshift galaxies
Multibaseline NenuFAR Interferometry in Transit Mode: Continuous Low-frequency Spectrum of the Crab Nebula. The Crab Nebula, a historical supernova remnant originating from the explosion recorded in 1054 CE, remains a cornerstone of multiwavelength astrophysical research. Its evolution across the radio, optical, and X-ray domains continues to be studied extensively. At low radio frequencies (&lt;100 MHz), accurate spectral measurements are hindered by strong scintillation effects from the compact central component. However, under favorable space weather and ionospheric conditions, reliable observations of the integrated spectrum become feasible. We present new low-frequency measurements of the Crab Nebula's integrated radio spectrum, obtained in 2025 using the New Extension in Nançay Upgrading LOFAR (NenuFAR) radio telescope, operating over the range 22─75 MHz. No significant flux decrease is detected between 1963 and 2025 within observational uncertainties. The full low-frequency spectral profile comprises two components: a compact source within the nebula and an extended shell contribution. The shell's flux density spectrum peaks at 2069 ± 200 Jy near 27.5 ± 0.5 MHz, consistent with a turnover caused by unshocked ejecta. Its spectral index between 50 and 70 MHz is ∼−0.36, following the convention Sν ∝ να, while the total spectrum follows a power law with index ∼−0.54. Free─free absorption modeling yields internal parameters of T ≍ 1000 K, ionization state Z ≍ 3.3, and emission measure EM ≍ 38 pc cm−6. The inferred electron density of the unshocked ejecta is ∼15 cm−3, corresponding to a mass of  ∼1.84−0.30+0.46M⊙ . These results are complemented by URAN─2 observations at 10.7, 16.7, 20.0, and 25.0 MHz.

Keywords: Galactic radio sources, Supernova remnants, Radio telescopes, Radio continuum emission, Radio interferometry, Radio astronomy, Radio sources
Investigating the System Configuration of Kepler-451 through Orbital Period Variations: Dynamical and Magnetic Interpretations. We present an analysis of eclipse timing variations in Kepler-451 using data spanning 2004─2024 from both ground- and space-based observations. Using two data sets, Data Set A (DS-A) and Data Set B (DS-B), we constructed updated O─C diagrams. By modeling both data sets with various light-travel time (LTT) configurations, we tested for the presence of circumbinary companions. For DS-A, the two-companion model (LTT34) provides the best fit with rms = 3.23 s and  χν2=1.23 , while adding a fifth body (LTT345) does not improve the fit (rms = 3.24 s,  χν2=1.28 ). For DS-B, the three-companion model (LTT345) yields the best fit (rms = 2.31 s,  χν2=1.01 ), although the semiamplitude of the inner companion (1.34 s) is smaller than the systematic error (1.81 s), suggesting it may originate from observational or calibration systematics. Applegate-mechanism tests indicate that most signals exceed the available energy budget, while the outer LTT terms in both data sets remain consistent with the Standard Model and may have a magnetic origin. Removing these magnetic terms yields dynamically stable configurations for at least 107 yr. These findings support the presence of a second-generation circumbinary planet at ∼3.4 au around Kepler-451, while the origin of the remaining LTT signals remains uncertain.

Keywords: Timing variation methods, Eclipsing binary minima timing method
The Carrying Capacity of the Solar Wind: Applications to Ion Escape. We present a physically motivated analytic framework for estimating solar wind mass-loading rates from ion sources using a simplified "particles in a box" (PIB) model. By applying conservation of energy and conservation of magnetic flux, we derive a general equation for the global pickup ion rate that explicitly accounts for both kinetic and electromagnetic (Poynting) energy fluxes supplied by the upstream wind and distributed to downstream particles and fields. Our analysis reveals that the global pickup rate may be fundamentally constrained by upstream wind parameters and the geometry of the interaction in a nontrivial manner. We further derive a theoretical upper limit to the maximum mass flux that a super-Alfvénic wind can transport. We call this limit the carrying capacity; it is an inherent property of the wind. We apply this framework to the Giotto flyby of Grigg─Skjellerup, and to unmagnetized and weakly magnetized terrestrial planets. The results suggest that the PIB framework may provide a useful big-picture approach for understanding and estimating stellar wind ion pickup in cometary and planetary environments inside and out of the solar system.

Keywords: Space plasmas, Atmospheric evolution, Plasma physics, Solar wind, Stellar magnetic fields, Pickup ions, Stellar winds, Alfven waves, Planetary magnetospheres, Exoplanet atmospheric evolution
Transferring Data from a Voronoi Mesh to an Adaptive Cartesian Grid in Pursuit of Self-consistent Top-down Star Formation. Unstructured Voronoi mesh simulations offer many advantages for simulating self-gravitating gas dynamics on galactic scales. Adaptive mesh refinement (AMR) can be a powerful tool for simulating the details of star cluster formation and gas dispersal by stellar feedback. Zooming in from galactic to local scales using the star cluster formation simulation package Torch requires transferring simulation data from one scale to the other. Therefore, we introduce VorAMR, a novel computational tool that interpolates data from an unstructured Voronoi mesh to an AMR Cartesian grid. VorAMR is integrated into the Torch package, which integrates the FLASH AMR magnetohydrodynamics code into the Astrophysical Multipurpose Software Environment. VorAMR interpolates data from an AREPO simulation to a FLASH AMR grid using a nearest-neighbor particle scheme, which can then be evolved within the Torch package, representing the first ever transfer of data from a Voronoi mesh to an AMR Cartesian grid. Interpolation from one numerical representation to another results in an error of a few percent in global mass and energy conservation, which could be reduced with higher-order interpolation of the Voronoi cells. We show that the postinterpolation Torch simulation evolves without numerical abnormalities. A preliminary Torch simulation is evolved for 3.22 Myr and compared to the original AREPO simulation over the same time period. We observe similarly distributed star cluster formation between the two simulations. More compact clusters are produced in the Torch simulation as well as 2.3 times as much stellar material as in AREPO, likely due to the differences in resolution.

Keywords: Star forming regions, Molecular clouds, Giant molecular clouds, Computational methods, Star clusters
Formation of Polyoxymethylenes in Extraterrestrial Ice Analogs of Formaldehyde Exposed to Ionizing Radiation. Polyoxymethylenes (POMs) have long been hypothesized as key organics in comets, as their decomposition products could account for the possible extended cometary formaldehyde (H2CO) source. However, POMs (X─(CH2O)n─Y; n &gt; 2) are hitherto unobserved in deep space, and their possible formation mechanisms have still remained elusive. Here, we report on the laboratory formation of formaldehyde oligomers (H─(CH2O)n─H; n = 2−4) within extraterrestrial ice analogs of formaldehyde exposed to energetic electrons simulating secondary electrons generated by galactic cosmic rays passing through ices. The potential identification of these short-chain-length POMs, such as methoxymethanol (CH3OCH2OH), (methoxymethoxy)methanol (CH3OCH2OCH2OH), and (methoxymethoxymethoxy)methanol (CH3OCH2OCH2OCH2OH), is accomplished by utilizing the synchrotron vacuum ultraviolet photoionization reflectron time-of-flight mass spectrometry (SVUV-PI-ReTOF-MS) technique coupled with the temperature-programmed desorption method. A radical-induced formaldehyde polymerization mechanism is proposed to address the formation of POMs, with the competition between chain propagation and chain termination determining the chain length of the polymers and availability of reactive hydrogen atoms. The electron impact ionization of POMs as well as accompanied fragmentation of their cations are analyzed via a quadrupole mass spectrometer, with mass peaks compared with those collected by the Positive Ion Cluster Composition Analyzer instrument on board the Giotto spacecraft in the inner coma of comet 1P/Halley, and by the Ptolemy instrument on the comet 67P/Churyumov─Gerasimenko. Our findings might support the proposal that (small) POMs exist on comets and nominate hitherto unobserved POMs such as (methoxymethoxy)methanol (CH3OCH2OCH2OH) and (methoxymethoxymethoxy)methanol (CH3OCH2OCH2OCH2OH) for future astronomical searches.

Keywords: Interstellar molecules, Mass spectrometry, Laboratory astrophysics, Astrochemistry, Surface ices, Comet volatiles
Characterizing Nanoflare Energy and Frequency through Field Line Analysis. We present a detailed analysis of a 3D MHD simulation of a subset of the magnetic flux in an active region. The simulation models the generation of nanoflares and response of the plasma to imposed photospheric motions. Our study focuses on characterizing the energy distribution and occurrence frequency of the nanoflares in the simulation that self-consistently heat the corona. This field line─based analysis reveals that the nanoflare energy distribution (energy per unit cross sectional area) follows a log-normal profile, where low-energy nanoflares are significantly more prevalent than those with high energy. When compared with the plasma cooling time, different energy nanoflares tend to repeat with different frequencies. Low-energy nanoflares repeat at high frequencies, while high-energy nanoflares repeat at low frequencies. However, the thermal evolution of plasma along the individual field lines is governed predominantly by the high-energy nanoflares. These findings provide critical insights into the role of small-scale magnetic reconnection events in heating the solar corona.

Keywords: Solar magnetic reconnection, The Sun, Solar coronal heating, Solar active regions, Solar physics
Inferring the Magnetic Field Configuration of an ICME From the In Situ Observations at Different Points. Interplanetary coronal mass ejections (ICMEs) would significantly influence the space environment when they encounter different planets, with their magnetic field configurations determining the level of such influences. Unfortunately, due to the lack of in situ observations, the magnetic field configurations of ICMEs in the heliosphere are only available at some special points. In this work, we present a novel model, called the Magnetic Field Configuration Inferring model, to reconstruct the magnetic field configuration of ICMEs using in situ observations from radial aligned observers. Originally, the model utilizes in situ magnetic field observations at a specified point as input data. A flux rope fitting model is applied to derive the magnetic field configuration at this point. Subsequently, the drag-based model and self-similar expansion assumption are incorporated to obtain the ICME parameters at the target point. Finally, the magnetic field configuration of the ICME at the target point is obtained based on the magnetic field and geometry parameters. We validate the model using two ICME events observed by Venus Express (VEX) and STEREO-A, showing the case of backcasting (STEREO-A to VEX) and forecasting (VEX to STEREO-A). The model results are well consistent with the observations except for some minor differences. These results demonstrate the model's ability to infer the magnetic field configuration of ICMEs at different points in the heliosphere based on in situ observations from one specified point. The model can be useful for space weather forecasting, especially for space weather predictions on other planets.

Keywords: Space weather, Interplanetary magnetic fields, Solar coronal mass ejections, Planetary science
Highly Polarized Intrinsic Emission and Its Orthogonal Counterpart in Vela X-1. Vela X-1 is one of the most archetypal wind-fed X-ray pulsars (XRPs), and the emergence of its orthogonal polarization states reveals distinctive polarimetric properties. Using data from Imaging X-ray Polarimetry Explorer observations of Vela X-1, we perform a polarization analysis of Vela X-1 using a triple power-law spectral model absorbed by varying column densities, successfully isolating two physically distinct orthogonal polarized components. The first polarized component corresponds to emission from the accretion mound surface that is not obscured by the wind clumps, with its polarization degree (PD) exceeding 30%. In specific phase intervals, the PD reaches 50.9% ± 10.7%. This marks the first detection of such highly polarized neutron star emission in an XRP. The second polarized component likely originates from complex physical processes within or near the accretion mound, with its PD showing a potential negative correlation with column density. Furthermore, by rotating the predicted polarization angle (PA) of the first polarized component by 90°, we successfully achieve separate fitting and simultaneous fitting of the two orthogonal polarization states using the rotating vector model.

Keywords: Neutron stars, Accretion, X-ray binary stars, High mass x-ray binary stars, Pulsars, Polarimetry
Formation of Multiple Dynamical Classes in the Kuiper Belt via Disk Dissipation. Planetesimal formation likely lasted for millions of years in the solar nebula, and the cold classicals in the Kuiper Belt are suggested to be the direct products of streaming instability. The presence of minor planetary bodies in the outer solar system and the exo-Kuiper belts provide key constraints to planet formation models. In this work, we connected dust drift and coagulation, planetesimal formation, N-body gravity, pebble accretion, planet migration, planetary core accretion, gap opening, and internal photoevaporation in one modeling framework. We demonstrate that multiple classes of minor planets, or planetesimals, can form during disk dissipation and remain afterwards, including a scattered group, a resonant group, and a dynamically cold group. Significant growth by pebble accretion was prevented by both dynamical heating due to the giant planet in the system and rapid dispersal of the disk toward the end of its lifetime. We also conducted a parameter study which showed that this is not a universal case, where the outcome is determined by the competition for dust between planetesimal formation and pebble accretion. Combining this scenario with sequential planet formation, this model provides a promising pathway toward an outer solar system formation model.

Keywords: Kuiper belt, Protoplanetary disks, Planetesimals, Debris disks, Planetary dynamics, Planet formation
Extreme Geomagnetic Storm on the Early Earth Induced by Corotating Interaction Regions from the Young Sun. Recent multiwavelength observations of young solar analogs suggest that the young Sun in the first 600 Myr was a magnetically active star that produced an X-ray and extreme-UV bright corona, fast, massive stellar wind, and energetic eruptive events. These outputs affected the magnetospheric environments of the early Earth and young rocky exoplanets. The interaction of the fast solar wind with the slow wind produced strong shocks from corotating interaction regions (CIRs) that provided high dynamic pressure on the magnetospheres of early Venus, Earth, and Mars. Here, we apply the Space Weather Modeling Framework, coupled with the Rice Convection Model, to simulate the response of the magnetospheric environments and associated Joule heating deposited in the upper atmosphere of the early Earth as it passed through a CIR shock from the young Sun. The model suggests a ∼40% closer dayside magnetopause standoff distance, and higher negative SYMH, cross polar cap potentials, atmospheric Joule heating, field-aligned currents, electron precipitations, and equatorward polar cap expansions, comparable to or exceeding those of recent intense and super geomagnetic storms. The magnetic storm produces dawn─dusk asymmetries in the polar cap boundary arising from the stellar magnetic field By. The proton density enhancements during the CIR event are the dominant factor in the overall dynamic pressure for resulting electron precipitation and Joule heating deposited into the Earth's ionosphere. We discuss implications for the magnetospheric states and associated habitability conditions on the early Earth and young rocky exoplanets around magnetically active solar-like stars.

Keywords: Magnetohydrodynamics, Solar analogs, Earth ionosphere, Stellar winds, Planetary magnetospheres, Corotating streams, Habitable planets, Magnetic storms
Atomic and Molecular Gas in the Milky Way. I. Structure Decomposition. We present GDCluster, a fully automated algorithm for decomposing a spectral-line data cube of interstellar gas into coherent structures. Assuming a multi-Gaussian nature of observed spectra, GDCluster employs and augments the derivative spectroscopy technique for precise parameter estimation, incorporates spatial-continuity constraints during spectral fitting, and extends these constraints to spatial clustering. This approach effectively resolves velocity blending structures in position-position-velocity (PPV) space—which is particularly critical for ubiquitous H I spectra where emissions from multiple phases are severely blended. Applied to the all-sky HI4PI data, a 10° × 10° CRAFTS survey region, and a 45° × 10° MWISP survey region, GDCluster extracts 45,299, 2247, and 47,119 structures in H I and CO (1─0), respectively. Comparative analyses demonstrate GDCluster's superiority over DBSCAN for separating overlapping spectra with complex velocity components.

Keywords: Molecular clouds, Neutral hydrogen clouds, Computational methods, Interstellar clouds, Interstellar medium