Sazuna/UAT_keywords huggingface dataset:
Model Spectrum of Ultrahigh-energy Cosmic Rays Accelerated in FR-I Radio Galaxy Jets. Nearby radio galaxies (RGs) of Fanaroff–Riley Class I (FR-I) are considered possible sites for the production of observed ultrahigh-energy cosmic rays (UHECRs). Among those, some exhibit blazar-like inner jets, while others display plume-like structures. We reproduce the flow dynamics of FR-I jets using relativistic hydrodynamic simulations. Subsequently, we track the transport and energization of cosmic ray (CR) particles within the simulated jet flows using Monte Carlo simulations. The key determinant of flow dynamics is the mean Lorentz factor of the jet-spine flow, &lt;Γ&gt;spine. When &lt;Γ&gt;spine ≳ 6, the jet spine remains almost unimpeded, but for &lt;Γ&gt;spine ≲ 3, substantial jet deceleration occurs. CRs gain energy mainly through diffusive shock acceleration for E ≲ 1 EeV and shear acceleration for E ≳ 1 EeV. The time-asymptotic energy spectrum of CRs escaping from the jet can be modeled by a double power law, transitioning from ∼E ‑0.6 to ∼E ‑2.6 around a break energy, E break, with an exponential cutoff at ${E}_{\mathrm{break}}\langle {\rm{\Gamma }}{\rangle }_{\mathrm{spine}}^{2}$ . E break is limited either by the Hillas confinement condition or by particle escape from the cocoon via fast spatial diffusion. The spectral slopes primarily arise from multiple episodes of shock and relativistic shear acceleration, and the confinement–escape processes within the cocoon. The exponential cutoff is determined by nongradual shear acceleration that boosts the energy of high-energy CRs by a factor of $\sim \langle {\rm{\Gamma }}{\rangle }_{\mathrm{spine}}^{2}$ . We suggest that the model spectrum derived in this work could be employed to investigate the contribution of RGs to the observed population of UHECRs.

Keywords: Relativistic jets, Fanaroff-Riley radio galaxies, Cosmic rays
TESS Stellar Rotation up to 80 Days in the Southern Continuous Viewing Zone. The Transiting Exoplanet Survey Satellite (TESS) mission delivers time-series photometry for millions of stars across the sky, offering a probe into stellar astrophysics, including rotation, on a population scale. However, light-curve systematics related to the satellite's 13.7 day orbit have prevented stellar rotation searches for periods longer than 13 days, putting the majority of stars beyond reach. Machine-learning methods have the ability to identify systematics and recover robust signals, enabling us to recover rotation periods up to 35 days for GK dwarfs and 80 days for M dwarfs. We present a catalog of 7245 rotation periods for cool dwarfs in the Southern Continuous Viewing Zone, estimated using convolutional neural networks. We find evidence for structure in the period distribution consistent with prior Kepler and K2 results, including a gap in 10–20 day cool-star periods thought to arise from a change in stellar spin-down or activity. Using a combination of spectroscopic and gyrochronologic constraints, we fit stellar evolution models to estimate masses and ages for stars with rotation periods. We find strong correlations between the detectability of rotation in TESS and the effective temperature, age, and metallicity of the stars. Finally, we investigate the relationships between rotation and newly obtained spot filling fractions estimated from Apache Point Observatory Galactic Evolution Experiment spectra. Field starspot filling fractions are elevated in the same temperature and period regime where open clusters' magnetic braking stalls, lending support to an internal shear mechanism that can produce both phenomena.

Keywords: Starspots, Computational astronomy, Stellar properties, Stellar populations, Light curves, Convolutional neural networks, Stellar activity, Stellar physics, Stellar rotation, Stellar evolution
Kindling the First Stars. I. Dependence of Detectability of the First Stars with JWST on the Population III Stellar Masses. The first Population III (Pop III) stars formed out of primordial, metal-free gas, in minihalos at z &gt; 20, and kickstarted the cosmic processes of reionization and enrichment. While these stars are likely more massive than their enriched counterparts, the current unknowns of their astrophysics include when the first Pop III stars ignited, how massive they were, and when and how the era of the first stars ended. Investigating these questions requires an exploration of a multidimensional parameter space, including the slope of the Pop III stellar initial mass function (IMF) and the strength of the nonionizing UV background. In this work, we present a novel model which treats both the slope and maximum mass of Pop III stars as truly free parameters while including the physics of the fragmentation of primordial gas. Our results also hint at a nonuniversal Pop III IMF which is dependent on the efficiency of primordial gas fragmentation. Our relatively simple model reproduces the results from hydrodynamic simulations, but with a computational efficiency which allows us to investigate the observable differences between a wide range of potential Pop III IMFs. In addition, the evolution of the number density of Pop III stars may provide insight into the evolution of the H2 dissociating background. While the slope of the Pop III IMF does not significantly affect the predicted number density of the first stars, more top-heavy IMFs produce Pop III star clusters which are 2–3 magnitudes brighter than their more bottom-heavy counterparts. While the Pop III star clusters are too dim for direct detection by JWST, we find they are within the reach of gravitational lensing.

Keywords: Theoretical models, Population III stars, N-body simulations
EMPRESS. XIII. Chemical Enrichment of Young Galaxies Near and Far at z ∼ 0 and 4–10: Fe/O, Ar/O, S/O, and N/O Measurements with a Comparison of Chemical Evolution Models. We present gas-phase elemental abundance ratios of thirteen local extremely metal-poor galaxies (EMPGs), including our new Keck/LRIS spectroscopy determinations together with 33 James Webb Space Telescope z ∼ 4–10 star-forming galaxies in the literature, and compare chemical evolution models. We develop chemical evolution models with the yields of core-collapse supernovae (CCSNe), Type Ia SNe, hypernovae (HNe), and pair-instability supernovae (PISNe), and compare the EMPGs and high-z galaxies in conjunction with dust depletion contributions. We find that high Fe/O values of EMPGs can (cannot) be explained by PISN metal enrichments (CCSN/HN enrichments even with the mixing-and-fallback mechanism enhancing iron abundance), while the observed Ar/O and S/O values are much smaller than the predictions of the PISN models. The abundance ratios of EMPGs can be explained by the combination of Type Ia SNe and CCSNe/HNe whose inner layers of argon and sulfur mostly fallback, which are comparable to the Sculptor stellar chemical abundance distribution, suggesting that early chemical enrichment has taken place in the EMPGs. Comparing our chemical evolution models with the star-forming galaxies at z ∼ 4–10, we find that the Ar/O and S/O ratios of the high-z galaxies are comparable to those of the CCSN/HN models, while the majority of high-z galaxies do not have constraints good enough to rule out contributions from PISNe. The high N/O ratio recently reported in GN-z11 cannot be explained even by rotating PISNe, but could be reproduced by the winds of rotating Wolf–Rayet stars that end up as a direct collapse.

Keywords: Galaxy formation, Galaxy chemical evolution, Dwarf galaxies, Chemical abundances, Chemical enrichment, Galaxy evolution, Sculptor dwarf elliptical galaxy
Criss-cross Nebula: A Case Study of Shock Regions with Resolved Microstructures at Scales of ∼1000 au. Using integral field spectroscopy (IFS) from MaNGA, we study the resolved microstructures in a shocked region in the Criss-cross Nebula (CCN), with an unprecedentedly high resolution of ≲1000 au. We measure surface brightness maps for 34 emission lines, which can be broadly divided into three categories: (1) the [O III] λ5007-like group including seven high-ionization lines and two [O II] auroral lines that uniformly present a remarkable lane structure, (2) the Hα λ6563-like group, including 23 low-ionization or recombination lines that present a clump-like structure, and (3) [O II] λ3726 and [O II] λ3729 showing high densities at both the [O III] λ5007 lane and the Hα clump. We use these measurements to constrain resolved shock models implemented in MAPPINGS V. We find our data can be reasonably well fitted by a model that includes a plane-parallel shock with a velocity of 133 ± 5 km s ‑1, plus an isotropic two-dimensional Gaussian component, which is likely another clump of gas ionized by photons from the shocked region, and a constant background. We compare the electron density and temperature profiles as predicted by our model with those calculated using observed emission-line ratios. We find different line ratios to provide inconsistent temperature maps, and the discrepancies can be attributed to observational effects caused by limited spatial resolution and projection of the shock geometry, as well as contamination of the additional Gaussian component. Implications on shock properties and perspectives on future IFS-based studies of the CCN are discussed.

Keywords: Shocks, Interstellar medium, Nebulae
Yet Another Sunshine Mystery: Unexpected Asymmetry in GeV Emission from the Solar Disk. The Sun is one of the most luminous γ-ray sources in the sky and continues to challenge our understanding of its high-energy emission mechanisms. This study provides an in-depth investigation of the solar disk γ-ray emission, using data from the Fermi Large Area Telescope spanning 2008 August to 2022 January. We focus on γ-ray events with energies exceeding 5 GeV, originating from 0.°5 angular aperture centered on the Sun, and implement stringent time cuts to minimize potential sample contaminants. We use a helioprojection method to resolve the γ-ray events relative to the solar rotation axes and combine statistical tests to investigate the distribution of events over the solar disk. We found that integrating observations over large time windows may overlook relevant asymmetrical features, which we reveal in this work through a refined time-dependent morphological analysis. We describe significant anisotropic trends and confirm compelling evidence of energy-dependent asymmetry in the solar disk γ-ray emission. Intriguingly, the asymmetric signature coincides with the Sun's polar field flip during the cycle 24 solar maximum, around 2014 June. Our findings suggest that the Sun's magnetic configuration plays a significant role in shaping the resulting γ-ray signature, highlighting a potential link between the observed anisotropies, solar cycle, and the solar magnetic fields. These insights pose substantial challenges to established emission models, prompting fresh perspectives on high-energy solar astrophysics.

Keywords: Solar cycle, High energy astrophysics, Solar gamma-ray emission, Quiet sun, Solar magnetic fields
rms–Flux Slope in MAXI J1820+070: A Measure of Disk–Corona Coupling. The linear rms–flux relation has been well established in different spectral states of all accreting systems. In this work, we study the evolution of the frequency-dependent rms–flux relation of MAXI J1820+070 during the initial decaying phase of its 2018 outburst with Insight-HXMT over a broad energy range of 1–150 keV. As the flux decreases, we first observe a linear rms–flux relation at frequencies from 2 mHz to 10 Hz, while such a relation breaks at varying times for different energies, leading to a substantial reduction in the slope. Moreover, we find that the low-frequency variability exhibits the highest sensitivity to the break, which occurs prior to the hard-to-hard state transition time determined through time-averaged spectroscopy, and the time deviation increases with energy. The overall evolution of the rms–flux slope and intercept suggests the presence of a two-component Comptonization system. One component is radially extended, explaining the strong disk–corona coupling before the break, while the other component extends vertically, contributing to a reduction of disk–corona coupling after the break. A further vertical expansion of the latter component is required to accommodate the dynamic evolution observed in the rms–flux slope. In conclusion, we suggest that the rms–flux slope in the 1–150 keV band can be employed as an indicator of disk–corona coupling, and the hard-to-hard state transition in MAXI J1820+070 could be partially driven by changes in the coronal geometry.

Keywords: Accretion, Black holes, High energy astrophysics
Formation of PSR J1012+5307 with an Extremely Low-mass White Dwarf: Testing Magnetic Braking Models. PSR J1012+5307 is a millisecond pulsar with an extremely low-mass white dwarf (WD) companion in an orbit of 14.5 hr. Magnetic braking (MB) plays an important role in influencing the orbital evolution of binary systems with a low-mass (≲1–2 M ⊙) donor star. At present, there exist several different MB descriptions. In this paper, we investigate the formation of PSR J1012+5307 as a probe to test plausible MB models. Employing a detailed stellar evolution model with the MESA code, we find that the convection- and rotation-boosted MB and "Intermediate" MB models can reproduce the WD mass, WD radius, WD surface gravity, neutron star mass, and orbital period observed in PSR J1012+5307. However, our simulated WD has a higher effective temperature than the observations. Three other MB mechanisms, including the standard MB model, are too weak to account for the observed orbital period in the Hubble time. A long cooling timescale caused by H-shell flashes of the WD may alleviate the discrepancy between the simulated effective temperature and the observed value.

Keywords: Neutron stars, Accretion, X-ray binary stars, White dwarf stars, Orbital evolution
Life in a Random Universe: Sciama's Argument Reconsidered. Random sampling in high dimensions has successfully been applied to phenomena as diverse as nuclear resonances, neural networks, and black hole evaporation. Here we revisit an elegant argument by the British physicist Dennis Sciama, who demonstrated that were our Universe random, it would almost certainly have a negligible chance for life. Under plausible assumptions, we show that a random universe can masquerade as "intelligently designed," with the fundamental constants instead appearing to be fined tuned to achieve the highest probability for life to occur. For our Universe, this mechanism may only require there to be around a dozen currently unknown fundamental constants. We speculate on broader applications for the mechanism we uncover.

Keywords: Cosmology, Search for extraterrestrial intelligence, Astrobiology, Anthropic principle
Prediction of Astrometric and Timing Microlensing Events with Pulsars by ATNF Catalog and Gaia DR3. Determining the mass of neutron stars is crucial for understanding their formation, evolution, and interior structure. Currently, only a few dozen neutron stars have had their masses measured, and most of them belong to binary systems. However, there are a huge number of isolated neutron stars with unknown masses. Microlensing events with neutron stars provide unique opportunities for knowing these compact objects. Astrometric microlensing with a background source lensed by a neutron star might be used to determine the neutron star's mass by measuring the deviation of the motion of the centroid of the images from its unlensed one. We search and predict these recent and future events based on the Australia Telescope National Facility Pulsar Catalog and Gaia DR3. We find 60 candidate astrometric microlensing events caused by neutron stars and the probability distributions of their observables by the Monte Carlo sampling. We also find four candidate "timing microlensing" events with a pulsar lensed by a foreground object that might be detected by timing measurements. While some of these events may be verified by future astrometric missions or pulsar-timing observations, we note that our prediction of these events is significantly restricted by the uncertainties of the available astrometric and timing measurements after assessing and comparing our results with previous works.

Keywords: Neutron stars, Astrometric microlensing effect, Gravitational lensing, Astrometry, Stellar masses
A Cacophony of Echoes from Daily Monitoring of the Crab Pulsar at Jodrell Bank. Using archival data from the 42-foot telescope at the Jodrell Bank Observatory, we produce daily stacks of aligned giant pulses for the Crab pulsar, to study changes to the daily profiles between 2012 April and 2016 December. From these, we identify echoes, where intervening material away from the line of sight causes pulsed emission to be redirected toward the observer, with delay corresponding to the increased distance of travel, resulting in additional profile components. These observations show that such echoes may be far more common than implied by the previous rate of detections. All the observed echoes are consistent with approaching zero delay at their closest approach to the normal giant pulse emission. This indicates that the structures responsible for producing these events must be highly anisotropic, with typical lengths greater than ∼4 au, typical widths on the sky of ∼0.1 au, and typical depths of ∼5 au, given the previously observed electron densities of the nebular filaments, on the order of 1000 cm‑3. This suggests that these inhomogeneities are likely to be offshoot substructure from the larger nebular filaments of the Crab nebula.

Keywords: Interstellar scattering, Radio bursts, Pulsar wind nebulae, Pulsars
Properties of Voids and Void Galaxies in the TNG300 Simulation. We investigate the properties of voids and void galaxies in the TNG300 simulation. Using a luminous galaxy catalog and a spherical void-finding algorithm, we identify 5078 voids at redshift z = 0. The voids cover 83% of the simulation volume and have a median radius of 4.4 h ‑1 Mpc. We identify two populations of field galaxies based on whether the galaxies reside within a void ("void galaxies"; 75,220 objects) or outside a void ("nonvoid galaxies"; 527,454 objects). Within the voids, mass does not directly trace light. Instead, the mean radial underdensity profile as defined by the locations of void galaxies is systematically lower than the mean radial underdensity profile as defined by the dark matter (i.e., the voids are more "devoid" of galaxies than they are of mass). Within the voids, the integrated underdensity profiles of the dark matter and the galaxies are independent of the local background density (i.e., voids-in-voids versus voids-in-clouds). Beyond the void radii, however, the integrated underdensity profiles of both the dark matter and the galaxies exhibit strong dependencies on the local background density. Compared to nonvoid galaxies, void galaxies are on average younger, less massive, bluer in color, less metal enriched, and have smaller radii. In addition, the specific star formation rates of void galaxies are ∼20% higher than nonvoid galaxies and, in the case of galaxies with central supermassive black holes with M BH ≳ 3 × 106 h ‑1 M ⊙, the fraction of active void galaxies is ∼25% higher than active nonvoid galaxies.

Keywords: Magnetohydrodynamical simulations, Voids, Galaxy evolution, Large-scale structure of the universe
Strategies for Obtaining Robust Spectral Energy Distribution Fitting Parameters for Galaxies at z ∼ 1 and z ∼ 2 in the Absence of Infrared Data. Robust estimation of star formation rates (SFRs) at higher redshifts (z ≳ 1) using UV–optical–near-infrared (NIR) photometry is contingent on the ability of spectral energy distribution (SED) fitting to constrain the dust attenuation, stellar metallicity, and star formation history (SFH) simultaneously. IR-derived dust luminosities can help break the degeneracy between these parameters, but IR data are often not available. Here, we explore strategies for SED fitting at z ≳ 1 in the absence of IR data using a sample of log M * &gt; 10.2 star-forming galaxies from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) for which 24 μm data are available. We adopt the total IR luminosity (L TIR) obtained from 24 μm as the "ground truth," which allows us to assess how well it can be recovered (as L dust) from UV–optical–NIR SED fitting. We test a variety of dust attenuation models, stellar population synthesis models, metallicity assumptions, and SFHs separately to identify which assumptions maximize the agreement (correlation and linearity) between L TIR and L dust. We find that a flexible dust attenuation law performs best. For stellar populations, we find that Bruzual &amp; Charlot models are favored over those of Eldridge et al. Fixing the stellar metallicity at solar value is preferred to other fixed values or leaving it as a free parameter. For SFHs, we find that minimizing the variability in the recent (&lt;100 Myr) SFH improves the agreement with L TIR. Finally, we provide a catalog of galaxy parameters (including M * and SFR) for CANDELS galaxies with $\mathrm{log}{M}_{* }\gt 8$ and 0.7 &lt; z &lt; 1.3, obtained using the models we found to be the most robust.

Keywords: Galaxy formation, Astronomical models, Galaxy properties, Model selection, Stellar populations, Star formation, Galaxy evolution, Spectral energy distribution, Galaxy masses, Metallicity, High-redshift galaxies, Galaxies
Cosmological Distance Measurement of Twelve Nearby Supernovae IIP with ROTSE-IIIb. We present cosmological analysis of 12 nearby (z &lt; 0.06) Type IIP supernovae (SNe IIP) observed with the ROTSE-IIIb telescope. To achieve precise photometry, we present a new image-differencing technique that is implemented for the first time on the ROTSE SN photometry pipeline. With this method, we find up to a 20% increase in the detection efficiency and significant reduction in residual rms scatter of the SN lightcurves when compared to the previous pipeline performance. We use the published optical spectra and broadband photometry of well-studied SNe IIP to establish temporal models for ejecta velocity and photospheric temperature evolution for our SNe IIP population. This study yields measurements that are competitive with other methods even when the data are limited to a single epoch during the photospheric phase of SNe IIP. Using the fully reduced ROTSE photometry and optical spectra, we apply these models to the respective photometric epochs for each SN in the ROTSE IIP sample. This facilitates the use of the Expanding Photosphere Method (EPM) to obtain distance estimates to their respective host galaxies. We then perform cosmological parameter fitting using these EPM distances, from which we measure the Hubble constant to be ${72.9}_{-4.3}^{+5.7}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ , which is consistent with the standard ΛCDM model values derived using other independent techniques.

Keywords: CCD photometry, Type II supernovae, Distance measure, Astronomy image processing, Spectroscopy, Supernovae, Galaxies