Sazuna/UAT_keywords huggingface dataset:
B-fields and Dust in Interstellar Filaments Using Dust Polarization (BALLAD-POL). IV. Grain Alignment Mechanisms in the Cocoon Nebula (IC 5146) Using Polarization Observations from JCMT/POL-2. The polarization of starlight and thermal dust emission from aligned nonspherical grains provides a powerful tool for tracing magnetic field morphologies and strengths in the diffuse interstellar medium to star-forming regions, and constraining the properties of dust grains and their alignment mechanisms. However, the physics of grain alignment is not yet fully understood. The alignment based on radiative torques (RATs), known as RAT alignment or the RAT-A mechanism, is the most acceptable mechanism. In this work, we investigate the grain alignment mechanisms in the F13 (F13N and F13C) and F13S filamentary regions of the Cocoon Nebula (IC 5146) using observations of polarized thermal dust emission from James Clerk Maxwell Telescope/POL-2 at 850 μm. We find that the polarization fraction decreases with increasing total intensity and gas column density in each region, termed a polarization hole. We investigate any role of magnetic field tangling in the observed polarization hole by estimating the polarization angle dispersion function. Our study finds that the polarization hole is not significantly influenced by magnetic field tangling, but is mainly due to the decrease in RAT alignment efficiency of grains in denser regions. To test whether the RAT-A mechanism can reproduce the observed results, we estimate the minimum alignment size of grains using RAT theory. Our study finds strong evidence for the RAT-A mechanism that can explain the polarization hole. We also find potential hints that the observed higher polarization fractions in some regions of the F13 filament can be due to the combined effects of both suprathermal rotation by RATs and enhanced magnetic relaxation, supporting the magnetically enhanced RAT mechanism.

Keywords: Interstellar dust, Interstellar magnetic fields, Star forming regions, Interstellar filaments
Introducing STARDIS: An Open and Modular Stellar Spectral Synthesis Code. We introduce a new 1D stellar spectral synthesis Python code called STARDIS. STARDIS is a modular, open-source radiative transfer code that is capable of spectral synthesis from near-UV to IR for FGK stars. We describe the structure, inputs, features, underlying physics, and assumptions of STARDIS, as well as the radiative transfer scheme implemented. To validate our code, we show spectral comparisons between STARDIS and KORG with the same input atmospheric structure models, and we also compare qualitatively to PHOENIX for solar models. We find that STARDIS generally agrees with KORG for solar models on the few-percent level or better, though the codes can diverge in the UV, with more extreme differences in cooler stars. STARDIS can be found at https://github.com/tardis-sn/stardis, and documentation can be found at https://tardis-sn.github.io/stardis/.

Keywords: Spectral line lists, Stellar abundances, K stars, Chemical abundances, G stars, Dwarf stars, Main sequence stars, Radiative transfer simulations, F stars, Astronomical simulations
XRISM Constrains Atmospheric Motion and Turbulent Dissipation in the Archetypal Radio-mode Feedback System Hydra-A. We present XRISM Resolve observations centered on Hydra-A, a redshift z = 0.054 brightest cluster galaxy, which hosts one of the largest and most powerful FR-I radio sources in the nearby Universe. We examine the effects of its high jet power on the velocity structure of the cluster's hot atmosphere. Hydra-A's central radio jets have inflated X-ray cavities with energies upward of 1061 erg. They reach altitudes of 225 kpc from the cluster center, well beyond the atmosphere's central cooling region. Resolve's 3'× 3' field of view covers 190 × 190 kpc, which encompasses most of the cooling volume. We find a one-dimensional atmospheric velocity dispersion across the volume of 164 ± 10 km s−1. The fraction in isotropic turbulence or unresolved bulk velocity is unknown. Assuming pure isotropic turbulence, the turbulent kinetic energy is 2.5% of the thermal energy radiated away over the cooling timescale, implying that kinetic energy must be supplied continually to offset cooling. While Hydra-A's radio jets are powerful enough to supply kinetic energy to the atmosphere at the observed level, turbulent dissipation alone would struggle to offset cooling throughout the cooling volume. The central galaxy's radial velocity is similar to the atmospheric velocity, with an offset of −37 ± 23 km s−1.

Keywords: Galaxy clusters, Intracluster medium, X-ray astronomy
A Hidden Pulse: Uncovering a New Timing Signal in Cygnus X-1 with AstroSat. The study of fast variability properties in X-ray binaries advances our understanding of the physical processes and geometric properties of the accretion flow around the compact object. In this work, we study the evolution of the timing properties of Cygnus X-1 with AstroSat/LAXPC, during the transition of the source from the hard to soft state in 2017. We use a novel frequency-segmented technique to fit simultaneously the cross spectra and parts of the power spectra and coherence function with a multi-Lorentzian model and predict the phase lags and the complementary parts of the power spectra and coherence function. We study the evolution of the frequency and power of the main variability components that are present throughout all the states. In particular, we identify previously undetected variability components, one of which manifests as a narrow dip in the coherence function and a broad drop in the phase-lag spectrum at the same frequency. This dip in coherence, which we detect for the first time in Cygnus X-1 at energies above 3 keV, appears in a state in which the source shows high-amplitude radio variability and significant hard X-ray polarization. While the contribution of the compact jet in X-rays is debated in the literature, this study provides a new avenue for investigating jet properties as well as the geometry of the Comptonizing medium.

Keywords: Accretion, X-ray binary stars, Stellar mass black holes, Time series analysis
Self-consistent JWST Census of Star Formation and AGN Activity at z = 5.5─13.5. The cosmic star formation history (CSFH) and cosmic active galactic nuclei (AGN) luminosity history (CAGNH) are self consistently measured at z = 5.5─13.5. This is achieved by analyzing galaxies detected by the James Webb Space Telescope from  ≍400arcmin2  fields from the Prime Extragalactic Areas of Reionization and Lensing Science, Cosmic Evolution Early Release Science, Next Generation Deep Extragalactic Exploratory Public, JWST Advanced Deep Extragalactic Survey, and Public Release IMaging for Extragalactic Research surveys. In particular, the combination of spectral energy distribution fitting codes, EAZY and PROSPECT, is employed to estimate the photometric redshifts and astrophysical quantities of 3751 distant galaxies, from which we compute the stellar mass, star formation rate, and AGN luminosity distribution functions in four redshift bins. Integrating the distribution functions, we find that the CSFH rises by ≍1 dex over z = 13.5─5.5, and the CAGNH rises by ≍1 dex over z = 10.5─5.5. We connect our results of the CSFH and CAGNH at z = 13.5─5.5 to that from z = 5─0 to determine the summary of ≳13 Gyr of star formation and AGN activity, from the very onset of galaxy formation to the present day.

Keywords: Galaxy formation, James Webb Space Telescope, Star formation, Active galactic nuclei, Galaxy evolution
Current Helicity in Response to Coronal Mass Ejections. Coronal mass ejections (CMEs), powerful solar eruptions with massive plasma ejected into the interplanetary space, are caused by the release of the magnetic free energy stored in coronal electric currents. Photospheric current helicity, defined as the integral of the product of the vertical electric current density and vertical magnetic field (Hc = ∫ jzBz dS), serves as a key parameter in understanding the eruptions. Using a 3D magnetohydrodynamic model, we identified a current helicity reversal pattern associated with the eruption: a pre-eruption decrease and a post-eruption increase. This helicity reversal is attributed to the redistribution of electric currents: before the eruption, currents concentrate toward the polarity inversion line (PIL); after the eruption they move away from the PIL, consistent with flare ribbon separation, which is caused by the upward progression of the reconnection site. To validate this pattern, we conducted an observational analysis of 50 ≥M5.0 eruptive flares. The results reveal that 58% of cases exhibit a pre-eruption decrease and 92% show a post-eruption increase in current helicity. Detailed analysis of two cases with this reversal suggests that they share the same current redistribution pattern, consistent with the mechanism identified in the simulations. Moreover, a pre-eruption decrease could be observed clearly even in the long-term evolution of the two cases. Current helicity can serve as an indicator of when electric currents are built up for the subsequent eruption, and it has the potential to predict CMEs to some extent.

Keywords: Solar coronal mass ejections, Solar flares, Solar photosphere
The Host Galaxies of Pulsar Timing Array Sources: Converting Supermassive Black Hole Binary Parameters into Electromagnetic Observables. Pulsar timing arrays (PTAs) are approaching the sensitivity required to resolve gravitational waves (GWs) from individual supermassive black hole (SMBH) binaries. However, the large uncertainty in source localization will make the identification of its host environment challenging. We show how to convert the posterior probability function of binary parameters inferred by GW analyses into distributions of apparent magnitudes of the host galaxy. We do so for a scenario in which the host environment is a regular early-type galaxy, and one in which it is an active galactic nucleus. We estimate the reach of PTAs in the near and intermediate future, and estimate whether the binary hosts will be detectable in all-sky electromagnetic (EM) surveys. A PTA with a baseline of 20 yr and 116 pulsars, resembling the upcoming data release of the International Pulsar Timing Array, can detect binaries out to a luminosity distance of 2 Gpc (corresponding to a redshift of z ∼ 0.36), while a PTA with a baseline of 30 yr and 200 pulsars can reach out to distances slightly greater than 3 Gpc (z ∼ 0.53). We find that the host galaxies of all binaries detectable with a baseline of 20 yr are expected to be present in the Wide-field Infrared Survey Explorer and SuperCOSMOS surveys, if they lie outside the plane of the Milky Way. The Two Micron All Sky Survey becomes incomplete for hosts of binaries more massive than 109.8M⊙ at a luminosity distance greater than 1 Gpc. The EM surveys become slightly more incomplete when PTAs with longer baselines and therefore improved sensitivities are considered.

Keywords: Gravitational wave astronomy, Supermassive black holes, Sky surveys
Domain Adaptation in Application to Gravitational Lens Finding. The next decade is expected to see a tenfold increase in the number of strong gravitational lenses, driven by new wide-field imaging surveys. To discover these rare objects, efficient automated detection methods need to be developed. In this work, we assess the performance of three domain adaptation (DA) techniques—adversarial discriminative DA, Wasserstein distance guided representation learning (WDGRL), and supervised domain adaptation (SDA)—in enhancing lens-finding algorithms trained on simulated data when applied to observations from the Hyper Suprime-Cam Subaru Strategic Program. We find that WDGRL combined with an equivariant-neural-network-based encoder provides the best performance in an unsupervised setting and that SDA is able to enhance the model's ability to distinguish between lenses and common similar-looking false positives, such as spiral galaxies, which is crucial for future lens surveys.

Keywords: Strong gravitational lensing, Astronomy data analysis
Detecting Land with Reflected-light Spectroscopy to Rule Out Waterworld O<SUB>2</SUB> Biosignature False Positives. The search for life outside our solar system is at the forefront of modern astronomy, and telescopes such as the Habitable Worlds Observatory (HWO) are being designed to identify biosignatures. Molecular oxygen, O2, is considered a promising indication of life, yet substantial abiotic O2 may accumulate from H2O photolysis and hydrogen escape on a lifeless, fully (100%) ocean-covered terrestrial planet when surface O2 sinks are suppressed. This so-called waterworld false-positive scenario could be ruled out with land detection because exposed land precludes extremely deep oceans (∼50 Earth oceans) given topographic limits set by the crushing strength of rocks. Land detection is possible because plausible geologic surfaces exhibit increasing reflectance with wavelength in the visible, whereas liquid water and ice/snow have flat or decreasing reflectance, respectively. Here, we present reflected-light retrievals to demonstrate that HWO could detect land on an exo-Earth in the disk-averaged spectrum. Given a signal-to-noise ratio (SNR) of 20 spectrum, Earth-like land fractions can be confidently detected with 0.3–1.1 μm spectral coverage (resolution R ∼ 140 in the visible, R ∼ 7 in the UV, with Earth-like atmosphere and clouds). We emphasize the need for UV spectroscopy down to at least 0.3 μm to break an O3–land degeneracy. We find that the SNR and resolution requirements in the visible/UV imply a large aperture (∼8 m) will be necessary to ensure the observing times required for land detection are feasible for most HWO terrestrial habitable zone targets. These results strongly inform the HWO minimum requirements to corroborate possible oxygen biosignatures.

Keywords: Radiative transfer simulations, Biosignatures, Exoplanets
Evolution of Supernova Remnants in a Cloudy Multiphase Interstellar Medium. We investigate the evolution of supernova remnants (SNRs) in a two-phase cloudy medium by performing a series of high-resolution (up to Δx ≈ 0.01 pc), 3D hydrodynamical simulations including radiative cooling and thermal conduction. We aim to reach a resolution that directly captures the shock–cloud interactions for the majority of the clouds initialized by the saturation of thermal instability. In comparison to the SNR in a uniform medium with the volume filling warm medium, the SNR expands similarly (following ∝ t 2/5) but sweeps up more mass as the cold clouds contribute before shocks in the warm medium become radiative. However, the SNR in a cloudy medium continuously loses energy after shocks toward the cold clouds cool, resulting in less hot gas mass, thermal energy, and terminal momentum. Thermal conduction has little effect on the dynamics of the SNR but smooths the morphology and modifies the internal structure by increasing the density of hot gas by a factor of ∼3–5. The simulation results are not fully consistent with many previous 1D models describing the SNR in a cloudy medium, including a mass loading term. By direct measurement in the simulations, we find that, apart from the mass source, the energy sink is also important with a spatially flat cooling rate  ė∝t‑11/5 . As an illustration, we show an example 1D model including both mass source and energy sink terms (in addition to the radiative cooling in the volume filling component) that better describes the structure of the simulated SNR.

Keywords: Supernova remnants, Ejecta, Supernovae, Interstellar medium
CHIME All-sky Multiday Pulsar Stacking Search (CHAMPSS): System Overview and First Discoveries. We describe the Canadian Hydrogen Intensity Mapping Experiment (CHIME) All-sky Multiday Pulsar Stacking Search (CHAMPSS) project. This novel radio pulsar survey revisits the full northern sky daily, offering unprecedented opportunity to detect highly intermittent pulsars, as well as faint sources via long-term data stacking. CHAMPSS uses the CHIME/FRB datastream, which consists of 1024 stationary beams streaming intensity data at 0.983 ms resolution, with 16,384 frequency channels across 400–800 MHz, continuously being searched for single, dispersed bursts/pulses. In CHAMPSS, data from adjacent east–west beams are combined to form a grid of tracking beams, allowing longer exposures at fixed positions. These tracking beams are dedispersed to many trial dispersion measures (DM) to a maximum DM beyond the Milky Way's expected contribution, and Fourier transformed in time to form power spectra. Repeated observations are searched daily to find intermittent sources, and power spectra of the same sky positions are incoherently stacked, increasing sensitivity to faint persistent sources. The 0.983 ms time resolution limits our sensitivity to millisecond pulsars; we have full sensitivity to pulsars with P &gt; 60 ms, with sensitivity gradually decreasing from 60 ms to 2 ms, as higher harmonics are beyond the Nyquist limit. In a commissioning survey, data covering ∼1/16 of the CHIME sky were processed and searched in quasi-realtime over two months, leading to the discovery of 11 new pulsars, each with S600 &gt; 0.1 mJy. When operating at scale, CHAMPSS will stack &gt;1 yr of data along each sightline, reaching a sensitivity of ≲30 μJy for all sightlines above a decl. of 10°, and off of the Galactic plane.

Keywords: Pulsars
Spatially Resolved Kinematics of SLACS Lens Galaxies. I. Data and Kinematic Classification. We obtain spatially resolved kinematics with the Keck Cosmic Web Imager (KCWI) integral-field spectrograph for a sample of 14 massive ( 11&lt;log10M*/M⊙&lt;12 ) lensing early-type galaxies at z ∼ 0.15─0.35 from the Sloan Lens ACS (SLACS) Survey. We integrate kinematic maps within the galaxy effective radius and examine the rotational and dispersion velocities, showing that 11/14 can be classified as slow rotators. The data set is unprecedented for galaxy-scale strong lenses in terms of signal-to-noise ratio (S/N), sampling, and calibration, vastly superseding previous studies. We find the primary contributions to systematic uncertainties to be the stellar template library and wavelength range of the spectral fit. Systematics are at the 1%─1.4% level, and positive covariance is &lt;1% between sample galaxies and between spatial bins. This enables cosmographic inference with lensing time delays with a &lt;2% uncertainty on H0. We examine the effects of integration of the data cubes within circular apertures of different sizes and compare with Sloan Digital Sky Survey (SDSS) single-aperture velocity dispersions. We conclude that the velocity dispersions extracted from SDSS spectra for these 14 SLACS galaxies, which have low S/N (∼9 Å─1) relative to the SLACS candidate parent sample, are subject to systematic errors (and covariance) due to stellar template library selection at the level of 3% (2%), which need to be added to the random errors. Comparison between our KCWI stellar velocity dispersions, our own analysis of SDSS spectra, and previously published measurements based on SDSS spectra shows mean differences within a few percent. However, these differences are not significant given the uncertainties of the SDSS-based stellar velocity dispersions. We find that the correlations between scaling relations using quantities inferred from dynamical, lensing, and stellar population models agree with previous SLACS analysis with no statistically significant change. A follow-up paper will present Jeans modeling in the context of broader studies of galaxy evolution and cosmology.

Keywords: Galaxies, Observational cosmology, Galaxy dynamics, Hubble constant, Galaxy kinematics, Early-type galaxies
A New Determination of the Mass of NGC 3603-A1: The Most Massive Binary Known?. The star NGC 3603-A1 has long been known to be a very massive binary, consisting of a pair of O2-3If*/WN5-6 stars which show Wolf─Rayet─like emission due to their luminosities being near the Eddington limit. The system has been poorly characterized until now, due to the difficulties of obtaining reliable radial velocities from broad, blended emission lines and the extreme crowding in the cluster. However, previously unpublished archival Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) spectra revealed that some of the upper Balmer lines (seen in absorption) are well separated at favorable orbital phases, prompting us to obtain our own carefully timed new HST/STIS spectra, which we have analyzed along with the older data. Radial velocities measured from these spectra allow us to obtain an orbit for this 3.77298-day binary. We also used archival STIS imaging of the cluster to obtain a more accurate light curve for this eclipsing system, which we then modeled, yielding the orbital inclination and providing values for the stellar radii and temperatures. Together, these data show that the NGC 3603-A1 system consists of a 93.3 ± 11.0M⊙ O3If*/WN6 primary with an effective temperature of 37,000 K, and a 70.4 ± 9.3M⊙ O3If*/WN5 secondary that is slightly hotter, 42,000 K. Although a more massive binary is known in the LMC, NGC 3603-A1 is as massive as any binary known in our own Galaxy for which a direct measurement of its mass has been made by a fundamental method. The secondary has been spun up by mass accretion from the primary, and we discuss the evolutionary status of this intriguing system.

Keywords: Massive stars, Binary stars, Stellar evolution
The Dynamics of Infall and Accretion Shocks in the Outer Disk. High-spatial-resolution observations of disks around young stars suggest planetary systems begin forming early, during the protostellar phase (≤1 Myr) when stars accrete most of their mass via infall from the surrounding cloud. During this era, shocks are expected to be ubiquitous around the gaseous accretion disk, due to supersonic infall that strikes the disk. We investigate the role of shocks using a theoretical and modeling framework we call the shock twist-angle Keplerian (STAK) disk, connecting the disk and infalling envelope gas via a shock using general physical principles. Briefly, at the shock, energy is dissipated while angular momentum is conserved, so that the infalling gas must change direction sharply, yielding a bend or twist in the streamlines. The model's pre-shock gas follows freefall parabolic trajectories, while the post-shock gas is on lower-energy, elliptical orbits. We construct synthetic observations and find that the deviations from circular Keplerian orbits are detectable in Doppler-shifted molecular spectral lines using radio interferometers such as ALMA. Specifically, the STAK model leads to line emission intensity and velocity-moment maps that are asymmetric and offset with respect to the disk structure traced by the dust continuum. We examine archival ALMA data for the class 0/I protostar L1527 and find the C18O velocity moment map has features resembling the disk-plus-envelope emissions that naturally arise when the two are connected by a shock. Thus, spectral line observations having sub-km s‑1 spectral resolution and angular resolution sufficient to fully resolve the disk can reveal protostars' envelope-disk shocks.

Keywords: Protostars, Shocks, Protoplanetary disks