Sazuna/UAT_keywords huggingface dataset:
Using Polarization to Uncover the Lyα Emission Mechanism in Lyα Nebulae. "Lyα nebulae" are immense (∼100 kpc) glowing gas clouds located in the distant universe, and the origin of their extended Lyα emission remains a mystery. Mapping their polarization offers critical insights, but imaging polarimetry to date has revealed polarization patterns that are difficult to interpret due to differences in the types and spatial configurations of their embedded sources. In this study, we more than double the sample size of polarization observations by targeting four additional Lyα nebulae: 4C41.17, SSA22-Sb3-LAB1, JACKPOT, and MAMMOTH-1, all of which host active galactic nuclei (AGN), from radio-loud to radio-quiet to type-I to type-II. Significant polarization is detected in three of these four nebulae, with polarization vectors distributed across the extended Lyα-emitting gas. In the two Lyα nebulae hosting radio-loud AGN, the polarization vectors exhibit a preferential alignment perpendicular to the radio jet direction, suggesting a scattering origin related to AGN outflows. In 4C41.17, JACKPOT, and MAMMOTH-1 (3/4 cases), the polarization strength shows a possible trend of increasing with radius. While the spatial patterns are complex and most large-radius measurements are upper limits, our results—together with previous work on three other targets—support the idea that scattering plays a key role in shaping the Lyα emission from these nebulae. Full interpretation requires direct comparison of these observations to radiative transfer models over a wide range of parameter space.

Keywords: Extragalactic astronomy, High-redshift galaxies, Polarimetry, Intergalactic medium
Variable X-Ray Reverberation in the Rapidly Accreting Active Galactic Nucleus Ark 564: The Response of the Soft Excess to the Changing Geometry of the Inner Accretion Flow. X-ray reverberation, which exploits the time delays between variability in different energy bands as a function of Fourier frequency, probes the structure of the inner accretion disks and X-ray coronae of active galactic nuclei. We present a systematic X-ray spectroscopic and reverberation study of the high-Eddington-ratio narrow-line Seyfert 1 galaxy Ark 564, using over 900 ks of XMM-Newton and NuSTAR observations spanning 13 yr. The time-averaged spectra can be well described by a model consisting of a coronal continuum, relativistic disk reflection, warm Comptonization, and three warm absorbers. Leveraging the high X-ray brightness of Ark 564, we are able to resolve the time evolution of the spectra and contemporaneous reverberation lags. The soft-band lag relative to the continuum increases with the X-ray flux, while Fe Kα lags are detected in only a subset of epochs and do not correlate with soft lags. Models based on a lamppost corona and reflection from a standard thin disk can broadly reproduce the observed lag-energy spectra of low-flux epochs; however, additional reverberation from the warm Comptonized atmosphere is required to explain the soft lags observed in high-flux epochs. A vertically puffed-up inner disk and a variable, vertically extended corona can better explain the observed evolution of the lags and covariance spectra. Our study underscores the importance of multiepoch, multiband analyses for a comprehensive understanding the inner accretion disk and corona.

Keywords: High energy astrophysics, Active galactic nuclei, Relativistic disks
A Detailed Analysis of the Milky Way Warp Based on Classical Cepheids. Classical Cepheids (CCs) are important probes for the large-scale warp structure of the Milky Way. Using Gaia Data Release 3 CCs, we establish an optimal time-dependent warp model, where the warp height increases with radius following a power law, the line of nodes (LONs) exhibit linear twisting with radius, following a leading spiral pattern, and the LONs undergo prograde evolution over time. Structurally, we identify significant warp features in the 5–9 kpc region of the Galactic disk, where the warp model performs better than the flat model. Beyond 15 kpc, the model with the second Fourier term does not fit the observations well, whereas the model with twisted LONs better matches the data. Kinematically, we derive expressions for the vertical velocities using direct differentiation and then calculate the precession rates for each CC. Our results intuitively indicate a nearly uniform and low warp precession rate of ω = 4.86 ± (0.88)stat ± (2.14)sys km s‑1 kpc‑1 beyond 12.5 kpc, in agreement with classical kinematic estimates. Based on these findings, we propose a simple yet comprehensive time-dependent warp model,  Zw(t)=0.00019R3.08sin(ϕ‑(3.87R‑41.79+4.86t)) , which provides a unified framework for describing both the geometric and kinematic evolution of the Galactic warp. We analyze the impact of the adopted solar vertical velocity on the inferred warp precession rate and confirm the reliability of the measured precession rate. In addition, we find that the extinction treatment affects the warp amplitude in the inner disk, while its influence on the outer-disk warp structure and the precession rate is negligible.

Keywords: Galaxy structure, Cepheid variable stars, Milky Way disk, Stellar kinematics
Unveiling the Galactic Baryon Cycle Process by an Empirical Model. We propose an empirical model to describe and constrain the baryon cycle process during galaxy evolution. This model utilizes the evolution of star formation rate, derived from the stellar mass–halo mass relations across different redshifts, and the cold gas content, derived from the NeutralUniverseMachine model, to constrain gas accretion and recycle of gas outflow in the model galaxy. Additionally, through detailed modeling of each cycle process, particularly the recycling process, and utilizing the gas-phase mass–metallicity relation at z = 0 as a constraint, our model establishes a relation between the recycle fraction and halo mass. It is found that the fraction of gas recycled from the outflow is a function of halo mass, with a value of 25% in galaxies with a halo mass of ∼1010.4M⊙, increasing to 75% in halos with a mass of ∼1012M⊙. We also find that the mass loading factor from the FIRE-2 simulation matches well with the constraints from both observational data and our model. Furthermore, using the gas content and metallicity of the circumgalactic medium (CGM) obtained from hydrodynamical simulations as constraints, our model predicts that, on average, 70% of universal baryon accretion is accreted to the halo and 80% of the nonrecycled gas in the outflow has escaped from the galaxy, entering the intergalactic medium (IGM). However, we note that future observational data are needed to finally constrain the mass and metal exchange between the CGM and the IGM.

Keywords: Galactic winds, Galaxy fountains, Galaxy chemical evolution, Galaxy evolution, Galaxy accretion, Circumgalactic medium
The Contribution of Turbulent Active Galactic Nucleus Coronae to the Diffuse Neutrino Flux. Active galactic nuclei (AGN) can accelerate protons to energies of ∼10─100 TeV, with secondary production of high-energy neutrinos. If the acceleration is driven by magnetized turbulence, the main properties of the resulting proton and neutrino spectra can be deduced based on insights from particle-in-cell simulations of magnetized turbulence. We have previously shown that these properties are consistent with the TeV neutrino signal observed from the nearby active galaxy NGC 1068. In this work, we extend this result to a population study. We show that the produced neutrino flux depends mainly on the energetics of the corona—the relative fractions of X-ray, magnetic, and nonthermal proton energy—and on the spectral energy distribution of the AGN. We find that coronae with similar properties can explain neutrinos from the candidate AGN for which IceCube has reported an excess, albeit less significant than NGC 1068. Building on this framework, we show how the neutrino signal evolves with AGN luminosity, and use this AGN sequence to predict the diffuse neutrino flux from the extragalactic population, showing that it can account for the diffuse neutrino signal observed by IceCube in the ∼1─100 TeV energy range.

Keywords: High energy astrophysics, Neutrino astronomy, Plasma astrophysics, Non-thermal radiation sources, Active galactic nuclei
UVIT Study of the Magellanic Clouds (U-SMAC). III. Hierarchical Star Formation in the Small Magellanic Cloud Regulated by Turbulence. The Small Magellanic Cloud (SMC), a satellite galaxy of the Milky Way, is an irregular dwarf galaxy exhibiting evidence of recent and ongoing star formation. We performed a spatial clustering analysis of far-ultraviolet stars in the SMC younger than 150 Myr using data from the Ultra Violet Imaging Telescope on board AstroSat. We identified 236 young stellar structures as surface overdensities at different significance levels. The sizes of these structures range from a few parsecs to several hundred parsecs. Their irregular morphologies are characterized by a perimeter–area dimension, derived from the projected boundaries of the young stellar structures, of Dp = 1.46 ± 0.4. The 2D fractal dimensions obtained from, respectively, the number–size relation and the size distribution are D2 = 1.64 ± 0.03 and D2 = 1.31 ± 0.16. These values indicate significant lumpiness among the young stellar structures. In addition, the surface density distribution of the identified structures follows a log-normal distribution. These features are strikingly similar to those of the turbulent interstellar medium, thus supporting the scenario of hierarchical star formation regulated by supersonic turbulence.

Keywords: Small Magellanic Cloud, Ultraviolet astronomy, Magellanic Clouds
Machine Learning Approach for Estimating Magnetic Field Strength in Galaxy Clusters from Synchrotron Emission. Magnetic fields play a crucial role in various astrophysical processes within the intracluster medium, including heat conduction, cosmic-ray acceleration, and the generation of synchrotron radiation. However, measuring magnetic field strength is typically challenging due to the limited availability of Faraday rotation measure sources. To address the challenge, we propose a novel method that employs Convolutional Neural Networks (CNNs) alongside synchrotron emission observations to estimate magnetic field strengths in galaxy clusters. Our CNN model is trained on either magnetohydrodynamic (MHD) turbulence simulations or MHD galaxy cluster simulations, which incorporate complex dynamics such as cluster mergers and sloshing motions. The results demonstrate that CNNs can effectively estimate magnetic field strengths with mean-squared error of approximately 0.135 µG2, 0.044 µG2, and 0.02 µG2 for β = 100, 200, and 500 conditions, respectively. Additionally, we have confirmed that our CNN model remains robust against noise and variations in viewing angles with sufficient training, ensuring reliable performance under a wide range of observational conditions. We compare the CNN approach with the traditional magnetic field strength estimate method that assumes equipartition between cosmic-ray electron energy and magnetic field energy. In contrast to the equipartition method, this CNN approach relies on the morphological feature of synchrotron images, offering a new perspective for complementing traditional estimates and enhancing our understanding of cosmic-ray acceleration mechanisms.

Keywords: Galaxy clusters, Convolutional neural networks, Magnetic fields, Intracluster medium, Radio astronomy
How Do Uncertainties in Galaxy Formation Physics Impact Field-level Galaxy Bias?. Our ability to extract cosmological information from galaxy surveys is limited by uncertainties in the galaxy–dark matter halo relationship for a given galaxy population, which are governed by the intricacies of galaxy formation. To quantify these uncertainties, we examine quenched and star-forming galaxies using two distinct approaches to modeling galaxy formation: UNIVERSEMACHINE, an empirical semianalytic model, and the ILLUSTRISTNG hydrodynamical simulation. We apply a second-order hybrid N-body perturbative bias expansion to each galaxy sample, enabling direct comparison of modeling approaches and revealing how uncertainties in the galaxy–halo connection affect bias parameters and non-Poisson noise across number densities and redshifts. Notably, we find that quenched and star-forming galaxies occupy distinct parts of the bias parameter space, and that the scatter induced from these different galaxy formation models is small when conditioned on similar selections of galaxies. We also detect the signature of assembly bias in our samples; this leads to small but significant deviations from analytic bias predictions, while assembly bias-removed samples match these predictions well. This work indicates that galaxy samples from a spectrum of reasonable, physically motivated models for galaxy formation give a relatively small range of field-level galaxy bias parameters. We estimate a set of priors from these models that should be useful in extracting cosmological constraints from luminous red galaxy– and emission line galaxy–like samples. Looking forward, careful estimates of the range of impacts of galaxy formation, for a given sample and cosmological analysis, will be an essential ingredient for extracting the most precise cosmological information from current and future large galaxy surveys.

Keywords: Cosmology, Galaxy formation, Cosmological perturbation theory, Large-scale structure of the universe
From UV-bright Galaxies to Early Disks: The Importance of Turbulent Star Formation in the Early Universe. Bursty star formation at early times can explain the surprising abundance of early UV-bright galaxies revealed by JWST but can also be a reason for the delayed formation of galactic disks in high-resolution cosmological simulations. We investigate this interplay in a cosmological simulation of an early-forming Milky Way analog with detailed modeling of the cold turbulent interstellar medium (ISM), star formation, and feedback. We find that the modeling of locally variable star formation efficiency (SFE) coupled with the ISM turbulence on the scales of star-forming regions is important for producing both early bursty evolution and early formation and survival of galactic disks. Such a model introduces a qualitatively new channel of the global star formation rate (SFR) burstiness caused by chaotic fluctuations in the average SFE due to changes in the ISM turbulence, which, in our simulation, dominates the short-term SFR variability. The average SFE stays low, close to ∼1% per freefall time, and its variation decreases when the gas disk forms, leading to only mild effects of stellar feedback on the early disk, enabling its survival. By rerunning our simulation with fixed SFE values, we explicitly show that low SFEs lead to smoother SFR histories and disk survival, while high SFEs lead to bursty SFRs and hinder disk formation. The model with variable SFE switches between these two regimes at the moment of disk formation. These trends are missing in more commonly used star formation prescriptions with fixed SFE; in particular, the prescriptions tying star formation to molecular gas should be interpreted with caution because the two are decoupled at early times, as we also show in this paper.

Keywords: Early universe, Galaxy formation, Hydrodynamical simulations, Galaxy disks, Milky Way disk, Star formation, Interstellar medium
Clump-fed Black Hole Growth in the First Billion Years of the Universe. Understanding how supermassive black holes (SMBHs) form in the early Universe is one of the most challenging problems in astrophysics. Their high abundance in the first billion years, as observed by the James Webb Space Telescope, hints toward black hole seeds that accrete mass rapidly. The origin of this accreted mass is not known. Here, we consider a billion solar mass clumpy galaxy at z = 5.48 with a 30 million solar mass black hole in the center. We show that the clumps should migrate to the central region because of torques from dynamical friction with the halo, funneling in at least 14 solar masses per year. This is fast enough to grow the observed SMBH, with only 1% of the accreted mass getting in and the rest going to a bulge. Clump-fed accretion could explain most young SMBHs because young galaxies are highly irregular with massive star-forming clumps.

Keywords: Accretion, Supermassive black holes, Galaxy kinematics, Spectral energy distribution, Lyman-alpha galaxies, Dynamical friction
High-resolution Radio Study of Pulsar Wind Nebula MSH 15─52 and Supernova Remnant RCW 89. We present high-resolution radio observations of the pulsar wind nebula (PWN) MSH 15─52, which is renowned for its distinctive handlike shape, and its associated supernova remnant RCW 89. Using the Australia Telescope Compact Array, we obtained 3 and 6 cm radio maps with a resolution of 2″. These unveil small-scale radio features in the system and allow a direct comparison with the arcsecond-resolution X-ray images. We find that the radio emission is composed of a complex filamentary structure. In particular, there is a bar-like feature across the central pulsar B1509−58 in the inner PWN, and the radio sheath wrapping around the pulsar also appears to be made up of filaments. Some prominent X-ray features are not detected in radio, including the one-sided jet in the south and the fingerlike structures in the north. These indicate turnover of the particle distribution at low energies in these regions. For RCW 89, the radio emission well coincides with both the X-ray knots and the Hα filaments. The high polarization fraction shows that the emission is synchrotron in nature, but it extends well beyond the sharp boundary of the nonthermal X-ray emission, which is difficult to explain.

Keywords: Supernova remnants, Polarimetry, Pulsar wind nebulae
Generation of Surface Sausage Oscillations of a Current Sheet and Propagating Magnetoacoustic Waves by Impulsive Reconnection. Magnetic reconnection and magnetohydrodynamic waves may well be both playing a role in coronal heating. In this paper, we simulate reconnection in the corona as a response to the convergence of opposite-polarity magnetic sources at the base of the corona. A current sheet forms at a magnetic null and undergoes impulsive bursty reconnection, which drives natural modes of oscillation of the current sheet by a process of symbiosis. These are leaky surface sausage modes, which cause the length of the current sheet to oscillate. Interaction of the oscillations and reconnection outflows with the magnetic Y-points at the ends of the sheet acts as sources for magnetoacoustic waves. Fast-mode waves propagate outward into the coronal environment, while slow-mode waves propagate along the separatrices extending from the ends of the current sheet. The periodicities for sausage oscillations of the current sheet, for the current sheet length, and for the propagating large-scale magnetoacoustic waves are all estimated to be approximately 91 s for the parameters of our experiment.

Keywords: Magnetohydrodynamics, Solar coronal heating, Solar coronal waves, Solar magnetic reconnection
MeerKAT 1.3 GHz Observations of the Wide-angle Tail Radio Galaxy J1712–2435. We present full-polarization MeerKAT images of the wide-angle tail, giant radio galaxy J1712‑2435 at 1.3 GHz with 7 .″ 5 resolution and an rms sensitivity of 8 μJy beam‑1. Due to its angular proximity to the Galactic center (l = 359 .° 6, b = +8 .° 5), the immediate environment is not well understood, but there are massive clusters nearby. Emission can be traced over an extent of 34 .' 6, which at the redshift of 0.024330 corresponds to a projected length of 1.02 Mpc. The inner jets are quite straight, but then bend and completely decollimate into extended plumes nearly orthogonal to the initial jet directions at a projected distance of approximately 100 kpc. The near-unity brightness ratio of the inner jets suggest that they are orientated within a few degrees of the plane of the sky. The 1400 MHz power is 3.9 × 1024 W Hz‑1, somewhat below the FRI/FRII divide. The total power emitted is estimated to be 5.6 × 1041 erg s‑1 over the range 10 MHz–100 GHz. The source dynamics are modeled with magnetohydrodynamics simulations; the result is a rough reproduction of the source's radio morphology/appearance. This study further highlights the merit of alternative scenarios, calling for future observational and numerical efforts.

Keywords: Radio jets, Radio plumes, Active galactic nuclei, Giant radio galaxies, Tailed radio galaxies
The Gap─Giant Association: Are Planets Hiding in the Gaps?. A handful of stars are known to host both an inner system of multiple transiting planets and an outer giant planet. These systems all feature a prominent gap between the orbits of two of the transiting planets, distinguishing them from typical multiplanet systems with more uniform orbital spacings. The reason for the association between inner gaps and outer giants is unknown. In this paper, we assess whether undiscovered planets might occupy these gaps in systems with outer giants. For each of the four relevant systems—Kepler-48, Kepler-65, Kepler-90, and Kepler-139—we found that a typical small planet (∼1─20 M⊕) could reside in the gap without inducing dynamical instability. However, in each case the gravitational influence of the outer giant planet is insufficient to tilt the orbit of the hypothetical planet by enough to prevent transits, strongly disfavoring a proposed theory for the observed gap─giant association. The gaps might instead contain smaller, undetected planets (≲ 1 R⊕), or be entirely devoid of planets.

Keywords: Transits, Extrasolar gaseous giant planets, Exoplanets, Planetary dynamics
Frequency Characteristics of Magnetosonic Waves Driven by Hot Ring-Beam Protons. Magnetosonic (MS) waves can be generated by energetic ring-beam protons, appearing as harmonics near the local proton cyclotron frequency, in the planetary ionospheres/magnetospheres. A theoretical dispersion relation is derived using kinetic theory to study the growth and frequency characteristics of these locally generated MS waves in a background of cold plasma consisting of electrons, protons, and heavier ions such as atomic and molecular oxygen ions. The real frequencies and linear growth rates are calculated numerically by choosing parameters relevant to the Martian dayside upper ionosphere, where ring-beam generated MS waves have been previously reported. The study reveals that the ring component plays a dominant role in determining the growth or damping rates of the waves, while the beam component shifts the growth peaks of each harmonic farther away from integer multiples of the local proton cyclotron frequency. This frequency shift is influenced by the harmonic number, beam energy, and propagation angle. An increase in harmonic number and beam energy increases the shift, which is further enhanced as the propagation angle deviates from 90°. While the numerical results are specific to Martian parameters, the theoretical framework presented here provides a generalized description of MS waves driven by hot ring-beam protons, relevant to diverse space plasma environments.

Keywords: Space plasmas, Mars, Planetary ionospheres, Planetary magnetospheres